Single-Step Construction of the anti-Deoxypropionate Motif from Propylene: Formal Total Synthesis of the Cuticular Hydrocarbons Isolated from Antitrogus parvulus

Reported herein is the single-step construction of an anti-configured deoxypropionate motif by syndiospecific propylene oligomerization catalyzed by a C_s -symmetric zirconocene complex. After oligomerization, oxidation of the oligomers by oxygen afforded oligopropylene alcohols in a single step. This strategy was applied to the single-step preparation of rel-(2R,4S,6R,8S)-2,4,6,8-tetramethylundecan-1-ol, the racemic mixture of the synthetic fragment of the cuticular hydrocarbons isolated from the cane beetle Antitrogus parvulus.

Identification, Synthesis, and Field Tests of the Sex Pheromone of Margarodes prieskaensis (Jakubski)

Here, we report the identification and synthesis of the sex pheromone of female Margarodes prieskaensis (Jakubski), and the attractiveness of the synthetic pheromone to males in field trapping tests. Volatile organic compounds were collected from virgin females using a sample enrichment probe (SEP). Analyses by gas chromatography coupled to mass spectrometry revealed the presence of only two constituents. By scaling up the SEP, sufficient of the major constituent was collected for ¹H and ¹³C nuclear magnetic resonance (NMR) analyses and ancillary NMR techniques. The sex attractant was identified as (2R,4R,6R,8R)-2,4,6,8-tetramethylundecan-1-ol. The enantiomerically pure compound was synthesized from octadecyl (2R,4R,6R,8R)-2,4,6,8-tetramethylundecanoate, a minor component of the uropygial (preen) gland secretion of the domestic goose, Anser domesticus. Field trapping experiments, carried out in vineyards in the Northern Cape Province of South Africa, showed that the synthetic compound was as attractive to winged males of M. prieskaensis as virgin females. The second compound detected was identified as the corresponding acetate, but addition of this did not affect the attractiveness of the major component. We believe this to be the first identification of a sex attractant of the Margarodidae.

Chiral methyl-branched pheromones

Insect pheromones are some of the most interesting natural products because they are utilized for interspecific communication between various insects, such as beetles, moths, ants, and cockroaches. A large number of compounds of many kinds have been identified as pheromone components, reflecting the diversity of insect species. While this review deals only with chiral methyl-branched pheromones, the chemical structures of more than one hundred non-terpene compounds have been determined by applying excellent analytical techniques. Furthermore, their stereoselective syntheses have been achieved by employing trustworthy chiral sources and ingenious enantioselective reactions. The information has been reviewed here not only to make them available for new research but also to understand the characteristic chemical structures of the chiral pheromones. Since biosynthetic studies are still limited, it might be meaningful to examine whether the structures, particularly the positions and configurations of the branched methyl groups, are correlated with the taxonomy of the pheromone producers and also with the function of the pheromones in communication systems.

Systematic comparison of sets of (13)C NMR spectra that are potentially identical. Confirmation of the configuration of a cuticular hydrocarbon from the cane beetle Antitrogus parvulus

A systematic process is introduced to compare (13)C NMR spectra of two (or more) candidate samples of known structure to a natural product sample of unknown structure. The process is designed for the case where the spectra involved can reasonably be expected to be very similar, perhaps even identical. It is first validated by using published (13)C NMR data sets for the natural product 4,6,8,10,16,18-hexamethyldocosane. Then the stereoselective total syntheses of two candidate isomers of the related 4,6,8,10,16-pentamethyldocosane natural product are described, and the process is applied to confidently assign the configuration of the natural product as (4S,6R,8R,10S,16S). This is accomplished even though the chemical shift differences between this isomer and its (16R)-epimer are only ±5-10 ppb (±0.005-0.01 ppm).

A general, asymmetric, and noniterative synthesis of trideoxypropionates. Straightforward syntheses of the pheromones (+)-vittatalactone and (+)-norvittatalactone

A novel, highly stereocontrolled, and very flexible synthetic access to biologically relevant trideoxypropionate building blocks in optically pure form has been developed. On the basis of a three-step sequence comprising a thermal oxy-Cope rearrangement, an iridium-catalyzed hydrogenation, and an auxiliary-controlled enolate methylation, trideoxypropionates with easily adjustable relative configuration were synthesized in excellent yields. In addition, the functionalized end groups allow for chemoselective manipulations and further elongation of the chain. The underlying strategy constitutes the first noniterative process for the assembly of polydeoxypropionates and has further been applied in total syntheses of the pheromones (+)-vittatalactone and (+)-norvittatalactone, which had been isolated from the striped cucumber beetle Acalymma vittatum.

Removable directing groups in organic synthesis and catalysis

Directing groups have been widely used in recent years to achieve control over all aspects of reaction selectivity in a wide range of transformations involving transition-metal catalysis and organometallic reagents. In cases when the existing functional group within a substrate is unsuited to achieve efficient intramolecular delivery of a reagent or catalyst, the specific introduction of an appropriately designed removable reagent-directing group can be a solution to this problem. In this Review we give an overview of the state of the art in this area, including the stoichiometric and catalytic use of directing groups.

A non-iterative, flexible, and highly stereoselective synthesis of polydeoxypropionates--synthesis of (+)-vittatalactone

A short sequence comprising an oxy-Cope rearrangement, iridium-catalyzed hydrogenation, and enolate methylation provides trideoxypropionates with excellent diastereocontrol. A straightforward synthesis of the cucumber beetle pheromone (+)-vittatalactone illustrates this new strategy.

Iterative strategies for the synthesis of deoxypropionates

This feature article gives an overview of iterative synthetic methods for the construction of deoxypropionates, an important class of polyketides. The catalytic and non-catalytic methodologies discussed are based on highly stereoselective reactions which can be carried out in an iterative fashion. Non-catalytic methods are described first, followed by state of the art catalytic iterative protocols. The application of the iterative methods in the synthesis of natural products is discussed as well.

Enantioselective total synthesis and determination of absolute configuration of vittatalactone

The first asymmetric total synthesis of vittatalactone features the divergent synthesis of two diastereomers to assign the absolute configuration of the natural product. Its consecutive propionate and deoxypropionate stereogenic centers are established by enantioselective o-DPPB directed allylic substitution.

Total synthesis of (+)-bourgeanic acid utilizing o-DPPB-directed allylic substitution

The lichen metabolite (+)-bourgeanic acid has been synthesized utilizing a new strategy for the construction of propionate motifs relying on the o-DPPB-directed copper-mediated allylic substitution. This synthesis features the o-DPPB-directed allylic substitution employing a chiral Grignard reagent, Sharpless asymmetric epoxidation, and reductive epoxide ring opening with a higher order dimethylcuprate to set the four stereogenic centers of the aliphatic depside.

A unified strategy for the stereospecific construction of propionates and acetate-propionates relying on a directed allylic substitution

Flexible friends: A new strategy that relies on o-DPPB-directed allylic substitution has been implemented for the flexible and stereospecific construction of major polyketide and isoprenoid structural elements (see scheme; o-DPPB=ortho-diphenylphosphanyl benzoate; PG=protecting group).