Determination of Residual Control and Concentration of Chlorantraniliprole in Soybean

Studies were conducted in 2020 and 2021 at the Delta Research and Extension Center in Stoneville, MS to determine concentrations of chlorantraniliprole (Prevathon, FMC Corporation, Philadelphia, PA) in soybean (Glycine max L.) leaves and florets. Chlorantraniliprole was applied as a foliar spray at four rates (0.028, 0.053, 0.078, 0.103 kg ai ha-1) for leaves and two rates (0.053, 0.078 kg ai ha-1) for florets. Leaf bioassays with corn earworm, Helicoverpa zea (Boddie), were conducted concurrently to determine mortality within three plant zones to evaluate chlorantraniliprole distribution throughout the canopy. For the leaf study, plants were partitioned into three zones consisting of a top (18th node), middle (13th node), and bottom (9th node) zone. Leaf samples from each zone were analyzed for chemical concentrations and bioassays were conducted at 1, 7, 14, 21, and 28 days after treatment (DAT). Floret samples were analyzed at 4, 7, 10, and 14 DAT. Concentrations of chlorantraniliprole, though variable, provided >71% control through all sampling dates, application rates, and canopy zones tested. Chlorantraniliprole was viable up to 28 DAT. Results from the soybean floret study suggested chlorantraniliprole was detected in florets up to 14 DAT. An additional leaf bioassay was conducted using concentrations detected in the floret study. Concentrations in florets provided mortality of corn earworm up to 48% out to 14 DAT. With a long residual expected, chlorantraniliprole applications should continue to be used to control corn earworm infestations in soybean and some additional control could be expected in florets.

Chlorantraniliprole Residual Control and Concentration Determination in Cotton

Studies were conducted in 2020 and 2021 at the Delta Research and Extension Center in Stoneville, MS, to determine the residual concentrations of chlorantraniliprole in cotton (Gossypium hirsutum, L.) leaves, as well as the concentrations in petals and anthers that developed after the time of application. Foliar applications of chlorantraniliprole were applied at four rates for leaves and two rates for petals and anthers at the second week of bloom. Additional bioassays were conducted to determine mortality of corn earworm (Helicoverpa zea, Boddie) in anthers. For the leaf study, plants were partitioned into three zones consisting of top, middle, and bottom zones. Leaf samples from each zone were analyzed for chemical concentrations at 1, 7, 14, 21, and 28 days after treatment (DAT). Residual concentrations, although variable, persisted through all sampling dates, rates, and zones tested. In this study, chlorantraniliprole remained detectable up to 28 DAT. Results from the cotton flower petal and anther studies detected concentrations of chlorantraniliprole in petals at 4, 7, 10, and 14 DAT, but no concentrations were detected in anthers. Therefore, no mortality of corn earworm was recorded in the anther bioassays. A series of diet-incorporated bioassays were conducted using concentrations previously found in the petal study to determine baseline susceptibilities of corn earworms and predicted mortality. Results from the diet-incorporated bioassays showed similar susceptibility in field and lab colony corn earworms. Concentrations of chlorantraniliprole could provide up to 64% control of corn earworm when feeding occurs on the petals.

Practical resistance to Cry toxins and efficacy of Vip3Aa in Bt cotton against Helicoverpa zea

BACKGROUND

Crops genetically engineered to make insect-killing proteins from Bacillus thuringiensis (Bt) have revolutionized management of some pests. However, the benefits of such transgenic crops are reduced when pests evolve resistance to Bt toxins. We evaluated resistance to Bt toxins and Bt cotton plants using laboratory bioassays and complementary field trials focusing on Helicoverpa zea, one of the most economically important pests of cotton and other crops in the United States.

RESULTS

The data from 235 laboratory bioassays demonstrate resistance to Cry1Ac, Cry1Fa, and Cry2Ab occurred in most of the 95 strains of H. zea derived from Arkansas, Louisiana, Mississippi, Tennessee, and Texas during 2016 to 2021. Complementary field data show efficacy decreased for Bt cotton producing Cry1Ac + Cry1Fa or Cry1Ac + Cry2Ab, but not Cry1Ac + Cry1Fa + Vip3Aa. Moreover, analysis of data paired by field site and year shows higher survival in bioassays was generally associated with lower efficacy of Bt cotton.

CONCLUSIONS

The results confirm and extend previous evidence showing widespread practical resistance of H. zea in the United States to the Cry toxins produced by Bt cotton and corn, but not to Vip3Aa. Despite deployment in combination with Cry toxins in Bt crops, Vip3Aa effectively acts as a single toxin against H. zea larvae that are highly resistant to Cry toxins. Furthermore, Vip3Aa adoption is increasing and previous work provided an early warning of field-evolved resistance. Thus, rigorous resistance management measures are needed to preserve the efficacy of Vip3Aa against this highly adaptable pest. © 2022 Society of Chemical Industry.

Standardized Field Trials in Cotton and Bioassays to Evaluate Resistance of Tobacco Thrips (Thysanoptera: Thripidae) to Insecticides in the Southern United States

Foliar-applied insecticide treatments may be necessary to manage thrips in cotton (Gossypium hirsutum L.) under severe infestations or when at-planting insecticide seed treatments do not provide satisfactory protection. The most common foliar-applied insecticide is acephate. Field observations in Tennessee suggest that the performance of acephate has declined. Thus, the first objective was to perform leaf-dip bioassays to assess if tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), in cotton production regions have evolved resistance to foliar-applied insecticides. A second objective was to assess the performance of commonly applied foliar insecticides for managing thrips in standardized field trials in Arkansas, Tennessee, Mississippi, and Texas. For both objectives, several insecticides were evaluated including acephate, dicrotophos, dimethoate, lambda-cyhalothrin, imidacloprid, and spinetoram. Field trials and bioassays were completed from 2018 to 2021. Dose-response bioassays with acephate were performed on tobacco thrips field populations and a susceptible laboratory population. Bioassay results suggest that tobacco thrips have developed resistance to acephate and other organophosphate insecticides; however, this resistance seems to be most severe in Arkansas, Tennessee, and the Delta region of Mississippi. Resistance to other classes of insecticides were perhaps even more evident in these bioassays. The performance of these insecticides in field trials was variable, with tobacco thrips only showing consistent signs of resistance to lambda-cyhalothrin. However, it is evident that many populations of tobacco thrips are resistant to multiple classes of insecticides. Further research is needed to determine heritability and resistance mechanism(s).

A Dynamic Threshold Approach for Tarnished Plant Bug (Hemiptera: Miridae) Management in the Midsouthern U.S. Cotton

One of the most economically important pests of cotton, Gossypium hirsutum L., in the midsouth region of the United States is the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois, Hemiptera: Miridae). Tarnished plant bug populations across the region have exhibited widespread resistance to numerous insecticide classes. To minimize late season resistance development, reducing unwarranted applications during the late flowering period can aid in resistance management and potentially reduce input costs. Trials were conducted during 2019 and 2020 to evaluate the impacts of tarnished plant bug populations in the later flowering period of cotton by modifying or terminating threshold regimes during the later weeks of bloom. Results showed that dynamic thresholds altered at the fourth week of bloom or later can reduce the number of late season applications made with no penalty to yield. Additionally, when utilizing a week of bloom termination approach, no significant yield losses were seen when terminating applications after the fourth week of bloom. These data may offer an alternative method to managing tarnished plant bug populations during the later flowering period of midsouth cotton.

Feeding Behavior and Fruiting Form Damage by Bollworm (Lepidoptera: Noctuidae) in Bt Cotton

Bt technologies have played a major role in the control of bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), in cotton. Variation in expression levels among varieties and plant parts, along with selection pressure on bollworm populations, has led to the development of resistance to some Bt proteins. Trials were conducted to evaluate how cotton varieties expressing different Bt proteins affect bollworm larval behavior and their damage in flowering cotton. Differences in larval recovery were observed among cotton varieties at 3 d with 3-gene Bt cotton having the lowest recovery and non-Bt cotton having the greatest recovery. Loss of bloom tags and abscission of small bolls at the site of infestation affected bollworm larval recovery among varieties. Day after infestation was the main factor that affected bollworm movement across all varieties. Number of total damaged fruiting forms by an individual bollworm larva was different among all varieties. Overall, flower bud (square) and fruit (boll) damage by an individual larva was lower on 3-gene cotton than 2-gene cotton and non-Bt cotton. An individual larva damaged fewer squares on 2-gene cotton than non-Bt cotton, but boll damage from bollworm was similar among 2-gene cotton and non-Bt cotton. The level of square and boll damage in 2-gene cotton has increased compared to previous research further supporting the occurrence of bollworm resistance to Cry proteins. The 3-gene cotton containing the Vip3A gene experienced low levels of damage and survival. These results will be important for improving management recommendations of bollworm in Bt cotton technologies.

Development of Economic Thresholds Toward Bollworm (Lepidoptera: Noctuidae), Management in Bt Cotton, and Assessment of the Benefits From Treating Bt Cotton With Insecticide

Widespread field-evolved resistance of bollworm [Helicoverpa zea (Boddie)] to Cry1 and Cry2 Bt proteins has threatened the utility of Bt cotton for managing bollworm. Consequently, foliar insecticide applications have been widely adopted to provide necessary additional control. Field experiments were conducted across the Mid-South and in Texas to devise economic thresholds for foliar insecticide applications targeting bollworm in cotton. Bt cotton technologies including TwinLink (TL; Cry1Ab+Cry2Ae), TwinLink Plus (TLP; Cry1Ab+Cry2Ae+Vip3Aa), Bollgard II (BG2; Cry1Ac+Cry2Ab), Bollgard 3 (BG3; Cry1Ac+Cry2Ab+Vip3Aa), WideStrike (WS; Cry1Ac+Cry1F), WideStrike 3 (WS3; Cry1Ac+Cry1F+Vip3Aa), and a non-Bt (NBT) variety were evaluated. Gain threshold, economic injury level, and economic thresholds were determined. A 6% fruiting form injury threshold was selected and compared with preventive treatments utilizing chlorantraniliprole. Additionally, the differences in yield from spraying bollworms was compared among Bt cotton technologies. The 6% fruiting form injury threshold resulted in a 25 and 75% reduction in insecticide applications relative to preventive sprays for WS and BG2, respectively. All Bt technologies tested in the current study exhibited a positive increase in yield from insecticide application. The frequency of yield increase from spraying WS was comparable to that of NBT. Significant yield increases due to insecticide application occurred less frequently in triple-gene Bt cotton. However, their frequencies were close to the dual-gene Bt cotton, except for WS. The results of our study suggest that 6% fruiting form injury is a viable threshold, and incorporating a vetted economic threshold into an Integrated Pest Management program targeting bollworm should improve the sustainability of cotton production.

Biology, Ecology, and Pest Management of the Tarnished Plant Bug, Lygus lineolaris (Palisot de Beauvois) in Southern Row Crops

Simple Summary

The tarnished plant bug, Lygus lineolaris, is a polyphagous, sap-feeder that causes significant economic damage in several field crops, especially cotton (Gossypium hirsutum L.) in the mid-southern United States. In 2020, it was reported that 4.8 million acres of cotton were infested by Lygus spp. in the United States. A broad host range, polyphagous feeding behavior and high mobility of this pest along with resistance development to conventional pesticides helped them establish as a significant pest of concern for cotton growers in the mid-south. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new research studies have been published on the Lygus biology, ecology, and integrated pest management strategies. A comprehensive review paper that summarizes these latest research developments and Lygus management strategies will be useful for researchers and cotton growers. In this review, we report and discuss the latest developments in Lygus research and the new control strategies that have been developed in the last two decades.

Abstract

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), (Hemiptera: Miridae) is considered the most damaging pest of cotton (Gossypium hirsutum L.) in the mid-southern United States, although it is established throughout the United States, southern Canada, and northern Mexico. The introduction of transgenic crops for the control of moths in the Heliothine complex and eradication of the boll weevil, Anthonomus grandis, from much of the United States led to greatly reduced pesticide use in cotton fields, which allowed L. lineolaris to emerge as a new primary pest of cotton in the mid-southern United States. Since the publication of a review by Layton (2000) on damage caused by Lygus lineolaris, many new studies have been published on the changes in host range, population dynamics, sampling methods and thresholds, cultural practices, sex pheromones and attractant blends, novel pesticides and insecticide resistance mechanisms, olfactory and feeding behaviors, introduction of biological control agents, host-plant resistance mechanisms, and new molecular and genetic tools for integrated pest management of Lygus species in cotton and other important crops. Here, we review and discuss the latest developments in L. lineolaris research in the last two decades.

Influence of Soil Moisture Zones on Rice Water Weevil (Coleoptera: Curculionidae) Populations in Furrow Irrigated Rice

Water conservation is an important factor for production of rice in the United States because of declining aquifer levels, but little research has been done to evaluate insect management in rice systems integrating water conservation practices. Rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important insect pest of rice in the U.S. Rice water weevil is a semiaquatic species that relies on flooded conditions to complete larval development, so water conservation practices are likely to impact their pest status. The study was conducted across the Mississippi River alluvial floodplain to compare rice water weevil population densities in different zones of a furrow irrigated rice field to a conventionally flooded rice field. All locations were sampled at 3, 4, and 5 wk after the initial irrigation. Larval densities were greatest in the lower end of furrow irrigated fields and in the adjacent flooded rice field compared with the upper and middle sections that did not hold standing water when averaged across three sample dates. Also, rice water weevil densities were greater during week five than week three. In terms of rice yields, the top third of furrow irrigated rice fields, the section that remained mostly dry, produced lower rough rice yields than all other sections and the flooded field. These results suggest that rice water weevil populations can be lower in a furrow irrigated rice system. As a result, more research is needed to determine whether a spatial management plan can be developed based on soil moisture zones in furrow irrigated rice.

Evaluation of Flood Removal in Combination with Insecticide Seed Treatment for Rice Water Weevil (Coleoptera: Curculionidae) Larval Management in Rice

An experiment was conducted at the Delta Research and Extension Center in Stoneville, MS during 2017 and 2018 to determine whether removal of the flood is an economical method of control for rice water weevil, Lissorhoptrus oryzophilus Kuschel. This experiment compared a continuous flood production system to draining a rice field completely and reestablishing a flood for the remainder of the growing season. In addition, two insecticide seed treatments, thiamethoxam and chlorantraniliprole, were compared with an untreated control within each system. Rice water weevil densities were measured prior to draining at 3 wk after flood and again after the flood was reestablished in drained plots. Rice water weevil densities were greater in 2017 than 2018. Chlorantraniliprole at the predrainage and postdrainage sample timing reduced larval numbers compared with the untreated control. The plots where water was removed until soil cracking then re-flooded had significantly lower weevil populations than plots that were continuously flooded during 2018 only. Draining of plots resulted in lower yields in 2018, but not in 2017. Additionally, both of the insecticide seed treatments resulted in greater yields and economic returns than the untreated control. Draining of flooded rice when rice water weevil larvae were present did not provide a consistent benefit, and may result in yield and economic penalties. Insecticide seed treatments consistently provided greater yield benefits in flooded rice. Based on these results, draining of flooded rice is not recommended to manage rice water weevil and insecticide seed treatments should be used to minimize economic losses.

Evaluation of Current Tarnished Plant Bug (Hemiptera: Miridae) Thresholds in Transgenic MON 88702 Cotton Expressing the Bt Cry51Aa2.834_16 Trait

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton in many areas of the southern United States. An experiment was conducted at two locations in Mississippi during 2016 and 2017 to evaluate action thresholds for tarnished plant bug on a novel Bacillus thuringiensis cotton that expresses the Cry51Aa2.834_16 toxin. Treatments included the current action threshold, a 2× threshold, and treatments where insecticides were only applied during the early season (preflower) or only during late season (during flowering) based on the current action thresholds. These were compared to an untreated control and a weekly insecticide use regime that received weekly insecticide sprays. All treatments were imposed on both Bt Cry1Aa2.834_16 cotton and a nontraited cotton. The Bt Cry1Aa2.834_16 trait reduced the number of tarnished plant bugs and injury, and improved yields compared to nontraited cotton. For all spray treatments except the weekly insecticide use regime, yields were greater for the Bt Cry51Aa2.834_16 cotton than the nontraited cotton. In terms of thresholds, Bt Cry1Aa2.834_16 cotton sprayed based on current action thresholds resulted in similar yields to the weekly insecticide use regime of both cotton types. In contrast, the 2× threshold resulted in lower yields than the current threshold for both cotton types. Though thresholds intermediate to the currently recommended action threshold and the 2× threshold were not tested, these data suggest that currently recommended action thresholds appear appropriate for Bt Cry51Aa2.834_16 cotton. These results suggest that this trait will be an important component of current IPM programs in cotton where tarnished plant bug is an important pest.

Euglobal-In-1, a new euglobal from Eucalyptus incrassata

From the juvenile leaves of Eucalyptus incrassata, a new euglobal having an acylphloroglucinol-sesquiterpene structure, euglobal-In-1 (1), has been isolated along with the known euglobal-III (2) and -V (3). The structure and stereochemistry of 1 were established by spectroscopic methods.

Monoalkylidenes of Meldrum's acid

Meldrum's acid has been found to react with equimolar quantities of aldehydes and secondary cyclic aliphatic amines to yield the corresponding Mannich bases which decompose under acidic conditions to afford the monoalkylidene derivatives in excellent yields.

Synthetic applications of intramolecular insertion in arylcarbenes. VII. Aryl-substituted benzocycloalkenylidenes

A series of benzo-fused cyclic carbenes, bearing suitably located alkoxy substituents in the phenyl ring, has been generated in the gas phase and pyrolysed at 250�/0.002-0.40 mm. In all cases, carbene insertion into the adjacent C-H bond (Bamford-Stevens insertion) occurs, either exclusively or predominantly, with up to 35% 1,5 C-H insertion in the alkoxy side chain to form peri-fused tricyclic heterocycles. These results are rationalized in terms of geometrical and electronic effects.

Synthetic applications of intramolecular insertion in arylcarbenes. VI. Ylid rearrangements in pyrolysis of o-alkylthiophenylcarbenes

Low-pressure thermal generation of a range of o-alkylthiophenylcarbenes produces, in addition to the normal insertion products, styrenes and 1,3-dihydrobenzo[c]thiophens-clearly arising from rearrangement. The main features of their mechanism of formation are established by deuterium-labelling studies: in both cases participation by S-ylids is implicated.

Plant growth regulators in Eucalyptus grandis. IV. Synthetic approaches to G-regulator analogues

A new synthetic approach is described to the plant growth regulators of the hexahydrobenzo[e]- 1,2-dioxin group (the G-regulators of Eucalyptus grandis). Condensation of 1,3-diketones with aldehydes under Lewis acid catalysis gives, in good yield, the 1 : 2 adducts (4H-1,3-dioxins); these are simultaneously cleaved and (with some exceptions) oxidized on silica gel to the desired structure. In this way synthesis of a number of G-regulator analogues of similar physiological activity has been achieved.

Plant growth regulators in Eucalyptus grandis. V. Synthesis of the G-regulators

Problems associated with earlier synthetic approaches to the G-regulators have been overcome by the use of the Mannich reaction in aprotic media. Under these conditions the Mannich base formed from the reaction of 1,3-diketones and aldehydes is stabilized by internal hydrogen bonding and can be isolated in high yield. In aqueous acid rapid elimination occurs to give the 2-methylene 1,3-diketones, which first enolize then add oxygen to generate the G-regulator structure. The steric limitations of the reactions are examined.

Plant growth regulators in Eucalyptus grandis. VI. Reaction of the G-regulators with nucleophiles

The formation of Michael adducts from the G-regulators and analogues with amines is described. Such adducts are, in general, unstable zwitterionic compounds and are decomposed by the action of acid into the parent G-regulator and the related 2-aminomethylene 1,3-diketone. Analogies are drawn with the natural storage and release in vivo.

Synthetic applications of intramolecular insertion in arylcarbenes. V o-Benzyl, phenylamino, phenoxy and phenylthio phenylcarbenes

The 2-(XC6H4)-substituted phenylcarbenes in which X = CH2, NH, O and S have been generated and pyrolysed in the gas phase at low pressure. When X = CH2 or NH, the main reaction is simple insertion into the adjacent o-position of the XC6H5 ring to give dihydroanthracenes and dihydroacridines respectively. The use of substituents shows that no spiro diene rearrangement is involved in the case X = NH. For X = O or S, on the other hand, the carbene inserts into the π-system ofthe XC6H5 ring and expansion occurs to give benzo[b]cyclohepta[d]furans and thiophens.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. II. o-Alkoxy-, Dialkylamino- and Alkylthio-phenylcarbenes

A series of phenylcarbenes, substituted in the ortho-position by alkoxy, dialkylamino and alkylthio side chains containing up to three carbon atoms, has been generated in the gas phase and pyrolysed at 250-750�/0.05-0.20mm. Carbene insertion occurs in moderate to high yield to give the appropriate five-and six-membered heterocyclics, the former predominating. The regioselectivity of the carbene insertion (five-membered ring us six-membered ring) is highest in the case of the alkoxy and dialkylamino compounds, where six-membered-ring formation is relatively minor; in the case of the alkylthiophenylcarbenes, the selectivity in favour of the smaller ring is, by comparison, small. The reasons for this are discussed in terms of the geometry of the transition state and the donor capacity of the heteroatom.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. III. Generation and Rearrangement of Aryloxycarbenes by Intramolecular Abstraction of Hydrogen

o-Alkoxy- and o-alkylthio-phenylcarbenes, generated by low-pressure pyrolysis in the gas phase, show abstraction of 2H across space to generate the corresponding o-tolyl vinyl ethers or sulfides. In the case of o-ethoxyphenylcarbene, deuterium labelling shows that this is a case of vicinal abstraction, not geminal abstraction followed by 1,2-hydride shift. o-Methoxyphenylcarbene, however, is similarly shown to undergo geminal hydrogen abstraction leading to o-tolyloxycarbene, which undergoes a 1,2-aryl shift to give o-tolualdehyde. Independent generation of aryloxycarbenes has been achieved by pyrolysis of 5-aryloxy-2,2-dimethyl-l,3-dioxan- 4,6-diones. The product carbenes show the expected rearrangement as well as normal insertion reactions.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. IV. o-Alkoxy-, Dialkylamino- and Alkylthio-1-phenylethylidenes

A series of 1-phenylethylidenes, substituted in the ortho-position by alkoxy, dialkylamino and alkylthio side chains containing up to three carbon atoms, has been generated in the gas phase and pyrolysed at 250-750�/0.05-0.30 mm. Carbene insertion to form five-membered heterocyclic rings predominates, with up to 20% Bamford-Stevens insertion, to give the styrenes; little or no formation of six-membered rings is observed. In cases where stereoselective insertion is possible, the trans-disubstituted heterocycle is formed preferentially, the selectivity being greatest in the case of dialkylamino substitution. The mechanisms involved are discussed in terms of transition state geometry.

Synthetic Applications of Intramolecular Insertion in Arylcarbenes. I. o-Alkylphenylcarbenes and 1-(o-Alkylphenyl)ethylidenes

A series of phenylcarbenes and 1-phenylethylidenes, substituted in the ortho-position by alkyl chains of 1-4 carbon atoms, has been generated in the gas phase and pyrolysed at 250-750°/0.05-0.10 mm. Apart from o-tolylcarbene, the phenylcarbenes show efficient insertion to form five- and six-membered rings, the former predominating. In the phenylethylidenes, Bamford-Stevens insertion into the adjacent methyl group competes with cyclization to an extent which decreases with chain length. At the same time, five-membered ring formation is greatly increased over six-membered ring formation, due to facilitation of out-of-plane twisting of the carbene atom. The mechanistic implications of the results are discussed in terms of an angular approach of the carbene p-orbital to the hydrogen atom under attack.

Iminyl radicals in gas-phase synthesis. III. Synthesis of a terminally unsaturated nitrile

The previously reported generation of α- and ω-cyanoalkyl radicals has been substantially improved by the use of the oxime esters of cyclopentanone and cyclohexanone instead of the azines. Fragmentationof the α-cyanoalkyl radicals to acrylonitrile is still observed, but the efficiency of alkylation of the residue is considerably enhanced. A synthetic device is described for intercepting the first-formedω-cyanoalkyl radicals with the formation of terminally unsaturated nitriles. This involves pyrolysis of the 5,6-dihydro-4H-l,2-oxazin-6-ones. The preparation and pyrolysis of 4,4a,5,6-tetrahydro-3H-naphth[l,2-c][1,2]oxazin-3-one to 2-(but-3-eny1)benzonitrile is described.

Iminyl radicals in gas-phase synthesis. I. Generation of nitriles by pyrolysis of aryl azines

Low-pressure gas-phase pyrolysis of aryl aldehyde azines leads to formation of the corresponding aryl cyanides in varying yield, together with small amounts of the corresponding stilbenes. In the case of benzaldehyde azine, stilbene formation is shown to be an intermolecular reaction. Certain substituent groups show some thermal decomposition, but this can be avoided by the use of the wines of alkyl aryl ketones; excellent nitrile yields are then obtained. The reaction is postulated as proceeding by unimolecular decomposition of the iminyl radicals formed by cleavage of the central N-N bond; thermochemical estimates are discussed. Azines from furan- and thiophen-2-carbaldehydes produce 1,2-di(2-furyl)ethylene-and 1,2-di(2- thienyl)ethylene respectively as well as the expected nitriles. As in the azines of alkyl aryl ketones, however, no alkenes are formed on pyrolysis of the azines from 2-acetylfuran and 2-acetylthiophen.

Iminyl radicals in gas-phase synthesis. II. Formation of a-branched nitriles from cycloalkanone azines

Gas-phase pyrolysis of cyclopentanone and cyclohexanone azines results in the formation of iminyl radicals. These undergo ring cleavage to the ω-cyanoalkyl radicals, which stabilize, by internal hydrogen-atom transfer, to the corresponding α-cyanoalkyl radicals. Fragmentation of the latter yields acrylonitrile and alkyl radicals, which can recombine with the α-cyanoalkyl radicals to form α-alkylated nitriles. The mechanisms involved are discussed with reference to isotopic labellingstudies.

The C6H5N energy surface. III. Isomerization processes and intramolecular trapping in picolylcarbenes

The synthesis is reported of a series of 5-(methyl-2-, -3- and -4- pyridyl)tetrazoles from the corresponding picolinecarbonitriles. These compounds are used as gas phase generators for the corresponding picolylcarbenes at 600�/0.05 mm. The normal isomerization process in arylcarbenes are interrupted in some cases by intramolecular trapping by the methyl groups, resulting in the first reported syntheses of cyclobuta-[b] and -[c]pyridines. The major process competing with this is that of nitrogen-extrusion to give tolylnitrenes, which then undergo ring contraction to form methyl-cyclopentadienecarbonitriles. The relative yields from these and other processes are used to deduce the preferred isomerization pathways in picolylcarbenes. In methyl-2- pyridylcarbenes there is almost exclusive insertion into the 2,3-bond, leading to the tolylnitrenes. The 3- and 4-pyridylcarbenes, however, show a tendency for the carbene centre to oscillate over the 3-, 4- and 5-positions of the ring with slower leakage to the 2-position.

The C6H5N energy surface. V. Isomerization of pyridylcarbenes to phenylnitrene - a 13C-labelling study

5-(2-, 3- and 4-Pyridyl)tetrazoles have been synthesized with a 13C- label at the 5-position and pyrolysed at 500-600� under reduced pressure to generate the corresponding pyridylcarbenes. Analysis of the aniline which results from their isomerization to phenylnitrene has been carried out by pulsed Fourier transform 13C N.M.R. The results show that, although both the cycloperambulatory (CP) and insertion-extrusion (IEP) mechanisms are operative, the latter predominates to a very great extent. As in the case of tolylcarbenes, this result is ascribed to a kinetic effect, i.e. the (largely irreversible) nitrogen extrusion step which generates phenylnitrene. The preferred modes of isomerization in the pyridylcarbenes are discussed.

The C6H5N energy surface. IV. Isotopic labelling studies in phenylnitrene isomerizations

Gas phase pyrolysis of phenyl azide gives rise to aniline, cyclopentadienecarbonitrile and pyridine as isomerization products from phenylnitrene. Isotopic labelling studies (14C, 13C) are used to examine the isomerization processes which occur in phenylnitrene prior to product formation. ��� At the lowest energy level of the intermediate little or no label randomization occurs and aniline evidently arises from hydrogen capture at this stage. Higher levels of the intermediate involve a cycloperambulatory motion of the nitrene nitrogen atom, followed by ring contraction to cyclo- pentadiene-1-carbonitrile. The pyridine formed possibly arises from a ring-expanded intermediate, which may not have undergone the cycloperambulation of the nitrene nitrogen atom. � The aniline and cyanocyclopentadiene derived from 5- pyridyltetrazole pyrolysis appear to exhibit very similar behaviour to those from phenyl azide as far as isotopic migration is concerned.

The C7H6 energy surface: phenylcarbene and 2-Methylene-3,5-cyclohexadienylidene - A duality of mechanism

The conversion of phenylcarbene (1) into fulvenallene (17) and ethynylcyclo-pentadiene (18) on gas-phase pyrolysis has been examined by 13C-tracer techniques. Complete randomization of all seven carbon atoms has been shown to precede ring contraction. The result is consistent with a pool of intermediates [cycloheptatrienylidene (19) and bicyclo[4,1,0]hepta-2,4,6-triene (21)], interconverting rapidly through tautomerism and concomitant H-shifts. Dimerization, intramolecular trapping, and ring contraction constitute the major exits from this pool. ��� Gas-phase thermolysis of indazole generates the same products (17)/(18) and in this case the mechanism has been investigated by the intramolecular trapping in 1-deutero-3-methylindazole to yield deuterostyrenes. Two pathways are revealed, proceeding respectively through phenylcarbene and 2-methylene-3,5-cyclohexadienyl-idene (36); factors affecting the latter pathway are discussed.

New alkaloids of Alstonia constricta

In the course of the isolation of reserpine from the tertiary alkaloids of Alstonia constricta root bark, a number of other alkaloids were obtained, and these alkaloids have now been the subject of further study. Alstonidine, a previously known alkaloid for which the provisional structure (6) was suggested, has now been shown to have the stereochemistry depicted in (7a). A new alkaloid, alstonilidine, has been shown to be (8). Vincamajine (9) has been identified, and two new alkaloids, O-3,4,5-trimethoxycinnamoylvincamajine (10) and 0-3,4,5-trimethoxybenzoylquebrachidine (11) have been isolated from the "reserpine concentrate". Another alkaloid, probably C43H50N4O7, appears to be a new member of the "bisindole" group.

Isothiazole chemistry. VI. Reactions of carbanions with N-Ethyl-3-isothiazolone

N-Ethyl-3-isothiazolone undergoes cleavage of the S-N bond when subjected to nucleophilic attack by carbanions, yielding a series of cis-3-alkylmercapto-acrylamides. Under basic conditions the reaction is shown to be reversible, the stability of the product being apparently dependent upon the degree of substitution at the carbanion site. Resonance-stabilized carbanions derived from primary carbon acids E-CH3 (E = electrophile) react with two moles of the isothiazolone to give E- CH(S-CH=CH-CONHEt)2 as well as E-CH2-S-CH=CH-CONHEt, whereas those derived from secondary carbon acids (E-CH2R) give only the product E- CHR-S-CH=CH=CONHEt. When carbanions from tertiary carbon acids E-CHR2 are employed, no stable product incorporating the carbon acid is obtained; a competing side reaction of the base on N-ethyl-3-isothiazolone itself results in the formation of a dimer (C5H7ONS)2. ��� It is proposed that the formation and subsequent stability of the products of carbanion attack depend upon their ability to form a carbanion adjacent to the sulphur atom, and that, in the absence of such a carbanion site, reversion to starting materials will be brought about by bases. Factors relevant to this are discussed.

Reactions of excited molecules. II. Reactions of phenylhydrazones on electron impact

Electron impact data are presented for the phenylhydrazones of a series of aromatic ketones C6H5-CO-R (R = H, CH3, CD3, C2H5, C6H6), and are discussed in comparison with the results of thermal excitation. Whereas pyrolysis resulted in extensive four-centre migration of R to nitrogen, followed by (or synchronous with) cleavage of the N-X bond, the electron-impact breakdown is largely dominated by N-N bond cleavage. A semi-quantitative assessment is made of the rearrangements which do occur, and the stereochemistry of these and related reactions is discussed.

Isothiazole chemistry. V. Acylation and acyl migration in 3-hydroxyisothiazole

In aprotic solvents acylation of 3-hydroxyisothiazole is subject to kinetic control, leading almost exclusively to the 3-acyloxyisothiazoles. On heating or standing a reversible O → N migration occurs, the final composition of the mixture depending on the nature of the acyl group. Where aliphatic acyl groups are involved (RCO: R = CH3, C2H5, C3H7, ClCH2, CH3O, C2H5O) the tendency towards migration to nitrogen is inversely related to the size of the group, whereas with aromatic groups (R = C6H5, 4-MeC6H4, 4-NO2C6H5, 3,5-(NO2)2C6H3, C6H5CH2), little or no N-acyl derivative results. Sulphonyl halides lead only to 0-sulphonyl derivatives, which presumably do not rearrange. The migration of the acyl group is shown to be intermolecular, involving both O + O and O → N migration, by the usual mixed migration experiments, and is catalysed by 3-hydroxyisothiazole and other nucleophiles. The greater thermodynamic stability of the O- or ,N-acyl derivatives, as revealed by equilibrium measurements, is seen to be a function of the steric requirements of the acyl group, the larger groups being more stable on oxygen. Examination of the infrared spectra reveals that this is probably due to out-of-plane twisting in the N-acyl-3- isothiazolones, which prevents N-CO overlap in all derivatives except the formyl which exists as 100% N-formyl at equilibrium.

Cyclic nitrones. II. Reactions of a cyclic α-keto nitrone with acetic anhydride, acetone, and methyl acetoacetate

The cyclic α-keto nitrone 3,4,5,6-tetrahydro-5,5-dimethyl-3-oxopyridine 1-oxide (III) when treated with acetic anhydride and sulphuric acid gave in low yield a compound (XI) having both enol lactone and vinylogous amide functional groups. Hydrolysis and decarboxylation of compound (XI) with aqueous potassium hydroxide gave a vinylogous amide (V), also obtained by acid- or base-catalysed condensation of compound (III) with isopropenyl acetate or acetone. Base-catalysed condensation of (III) with methyl acetoacetate gave an ester (XVII) closely related to compound (V).

Isothiazole chemistry. IV. Cyanide cleavage of the S-N bond in 3-hydroxyisothiazole

Nucleophilic attack on 3-hydroxyisothiazole by cyanide ion, yielding cis-3-thiocyanoacrylamide, has been investigated over the pH range 0.00-5.50. Rate constants have been measured both for direct attack by cyanide ion and from the effect of cyanide ion in retarding the cyclization of the thiocyanoacrylamide; in both cases the derived rate constants agree. The pH-rate profile of the reaction reveals the existence of two kinetically discrete mechanisms. Within the range 5.50-4.00 the dominating mechanism is one involving a slow direct attack on 3-hydroxyisothiazole itself, while at pH less than 3.50 the conjugate acid of this molecule is subjected to a much faster attack. Equilibrium studies have been made for the system, and the effect of temperature on the equilibrium constant has been used to derive thermodynamic parameters.

Isothiazole chemistry. III. Kinetics and mechanism of cyclization of cis-3-Thiocyanoacrylamide

The cyclization of cis-3-thiocyanoacrylamide to isothiazol-3-one has been studied over the pH range 0-5.5 and it is shown that two cyclization mechanisms exist. Within the pH range 5.5-3.5, the only important mechanism is one involving a rapid, unimolecular cyclization of the thiocyanoacrylamide anion, while at pH less than 3.00, the process is essentially a slow cyclization of the neutral molecule, followed by rapid proton loss. The large rate difference between the two mechanisms is ascribed to a lowering of ΔF* in the anion cyclization mechanism by a more favourable TΔS* term, and possible reasons for this are discussed.

Chemical constituents of Eriococcus confusus Maskell. I. The quinonoid pigments

Eriococcus confusus Maskell., growing on both Eucalyptus caesia and maculosa, contains a number of anthraquinone pigments. Emodin has been identified as one of the major components, and the other is tentatively assigned the structure 1,2,3,8-tetrahydroxy-6-methylanthrquinone. Chromatographic and p.m.r, data are presented for a number of anthraquinones, including the new compounds 1,3,5-trihydroxy-6- methylanthraquinone and 1,3,5-trihydroxy-7-methylanthraquinone. In addition to the pigments, the insects are covered with a waxy secretion, which probably consists of a mixture of long-chain, saturated ketones in the C20-C24 range.

Reactions of excited molecules. I. A thermal four-centre migration in phenylhydrazones

Phenylhydrazones of carbonyl compounds C6H5-CO-R (R = H, Me, Et, Ph) have been subjected to vapour-phase pyrolysis at temperatures ranging from 650 to 1100�K. Analysis of the products indicates that a four-centre reaction is involved in which the group R migrates to the α- nitrogen of the phenylhydrazone moiety, with a concomitant production of benzonitrile. The mechanisms of this and competing reactions are discussed.

Alkaloids of the Australian Rutaceae: Halfordia scleroxyla. III. Mass spectrometry of halfordinol and related oxazoles

Comparative studies by mass spectrometry of halfordinol [2-(3-pyridy1)-5-(4-hydroxyphenyl)oxazole] and other derivatives of the new oxazole alkaloid N-methylhalfordinium chloride with model aryloxazoles confirmed the structure of the alkaloid. One of the main features of the decomposition of 2,5-diaryloxazole ions in the mass spectrometer involved a novel concerted elimination of HCN and CO. A mechanism has been proposed for this and other reactions of oxazole ions, including those of 4,5- and 2,4-diphenyl derivatives.

Alkaloids of the Australian Rutaceae: Halfordia scleroxyla. II. Isolation and structure of the alkaloids

The bark of Halfordia scleroxyla contains the tertiary bases halfordine, C19H20O4N2 (II), halfordinone, C19H18O3N2 (III), and halfordinol, C14H10O2N2 (IV), together with the yellow quaternary base N-methylhalfordinium chloride, C20H23O4N2+Cl- (I). These alkaloids are derivatives of 2(3'-pyridyl)-5-(4"-hydroxyphenyl)oxazole; physical and chemical evidence for the structural assignments is presented.

Alkaloids of the Australian Apocynaceae: Kopsia longiflora Merr. III. Preliminary Degradation of the Alkaloids

Graded alkaline hydrolysis of the monoacid tertiary bases kopsiflorine (C23H28O5N2), kopsilongine (C24H30O6N2), and kopsamine (C24H28O7N2) shows that they contain two methoxycarbonyl groups. All but one of the residual oxygen atoms are accounted for as aromatic ether linkages. One of the methoxycarbonyl groups is responsible for the deactivation of the other nitrogen atom (N(a)) present, since anew basic centre is generated by partial hydrolysis and subsequent decarboxylation of the acid produced. The alkaloids are tentatively formulated as blocked indoline bases containing a urethane grouping at N(a). The fourth alkaloid, kopsinine (C21H26O2N2) is similarly formulated, but in this case N(a) is weakly basic, the urethane methoxycarbonyl group and the additional oxygen atom being absent.

The Alkaloids of Lupinus varius L. III. The Structure of Base LV-1

Base LV-1 (C15H220N2), isolated from the seeds and tops of Lupinus varius L., is converted by catalytic hydrogenation to (-)-sparteine. Partial reduction yields a ketonic base C15H240N2, shown to be 4-oxosparteine, and a study of the physical properties of base LV-1 leads to the alternative structures, Δ2- and Δ5-dehydro-4-oxosparteine. Decision between these alternatives is reached by examination of the nuclear magnetic resonance spectrum, which shows the presence of two vinyl hydrogen atoms, that is, base LV-1 is (-)-Δ2-dehydro-4-oxosparteine. Base LV-1 has been shown to be identical with multiflorine, isolated by Comin and Deulofeu (1959) from L. multiflorus Lam.

The stereochemistry and Hofmann degradation of Lupinine methiodides

Optical rotation studies on the epimers (-)-lupinine and (+)-epilupinine and their methiodides lead to the conclusion that while (+)-epilupinine methiodide has the normal trans-ring junction, (-)-lupinine methiodide has a cis-ring junction. Unlike the quaternary salts of cryptopleurine, canadine, and tetrahydropalmatine, neither of the lupinine methiodides could be racemized by refluxing with alkali.

The Alkaloids of Lupinus varius L. II. Alkaloids of the Leaf

The aerial parts of Lupinus varius L. contain the alkaloids LV-I (0.10 per cent.) and (+)-epilupinine (0.50 per cent.) previously reported in the seeds, together with (-)-sparteine (0.006 per cent.) and small amounts of two mono-nitrogen bases LV-3 (C20H27O4N, containing one methoxyl group) and LT7-4 (C17H23O5N). The proportion of LV-1 present in the leaves is higher than that in the seeds, while the amount of (+)-epilupinine-N-oxide is much lower.