Facile access to C-substituted piperazin-2-ones and mianserin derivative enabled by chemoselective carbene insertion and cyclization cascade

The chemoselective N-H insertion of unsymmetrical diamines into carbene is a longstanding challenge. A simple copper-catalyzed strategy for synthesizing C-substituted piperazinones is described, employing easily accessible diazo compounds and 1,2-diamines. The reaction proceeded via chemo-selective carbene insertion at the comparatively less nucleophilic amine, followed by instantaneous cyclization. The protocol was further extended to access NH-free piperazinone, and the synthesis of a Mianserin derivative.

Insecticidal and Repellent Properties of Rapid-Acting Fluorine-Containing Compounds against Aedes aegypti Mosquitoes

The development of safe and potent insecticides remains an integral part of a multifaceted strategy to effectively control human-disease-transmitting insect vectors. Incorporating fluorine can dramatically alter the physiochemical properties and bioavailability of insecticides. For example, 1,1,1-trichloro-2,2-bis(4-fluorophenyl)ethane (DFDT)─a difluoro congener of trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)─was demonstrated previously to be 10-fold less toxic to mosquitoes than DDT in terms of LD50 values, but it exhibited a 4-fold faster knockdown. Described herein is the discovery of fluorine-containing 1-aryl-2,2,2-trichloro-ethan-1-ols (FTEs, for fluorophenyl-trichloromethyl-ethanols). FTEs, particularly per-fluorophenyl-trichloromethyl-ethanol (PFTE), exhibited rapid knockdown not only against Drosophila melanogaster but also against susceptible and resistant Aedes aegypti mosquitoes, major vectors of Dengue, Zika, yellow fever, and Chikungunya viruses. The R enantiomer of any chiral FTE, synthesized enantioselectively, exhibited faster knockdown than its corresponding S enantiomer. PFTE does not prolong the opening of mosquito sodium channels that are characteristic of the action of DDT and pyrethroid insecticides. In addition, pyrethroid/DDT-resistant Ae. aegypti strains having enhanced P450-mediated detoxification and/or carrying sodium channel mutations that confer knockdown resistance were not cross-resistant to PFTE. These results indicate a mechanism of PFTE insecticidal action distinct from that of pyrethroids or DDT. Furthermore, PFTE elicited spatial repellency at concentrations as low as 10 ppm in a hand-in-cage assay. PFTE and MFTE were found to possess low mammalian toxicity. These results suggest the substantial potential of FTEs as a new class of compounds for controlling insect vectors, including pyrethroid/DDT-resistant mosquitoes. Further investigations of FTE insecticidal and repellency mechanisms could provide important insights into how incorporation of fluorine influences the rapid lethality and mosquito sensing.

Pd-catalyzed synthesis of 1-(hetero)aryl-2,2,2-trichloroethanols using chloral hydrate and (hetero)arylboroxines

1-(Hetero)aryl-2,2,2-trichloroethanols are useful key intermediates for the synthesis of various bioactive compounds. Herein, we describe N-heterocyclic carbene (NHC)-coordinated cyclometallated palladium complex (CYP)-catalyzed (hetero)aryl addition of chloral hydrate using (hetero)arylboroxines, providing a new approach to 1-(hetero)aryl-2,2,2-trichloroethanols. Notably, PhS-IPent-CYP which coordinated the bulky yet flexible 2,6-di(pentan-3-yl)aniline (IPent)-based NHC showed good catalytic activities and promoted the transformation in 24-97% yields.

Pyrrole-Based Conjugated Microporous Polymers as Efficient Heterogeneous Catalysts for Knoevenagel Condensation

Conjugated microporous polymers (CMPs) with robust architectures, facilely tunable pore sizes and large specific surface areas have emerged as an important class of porous materials due to their demonstrated prospects in various fields, e.g. gas storage/separation and heterogeneous catalysis. Herein, two new pyrrole-based CMPs with large specific surface areas and good stabilities were successfully prepared by one-step oxidative self-polycondensation of 1,2,4,5-tetra (pyrrol-2-ly)benzene or 1,3,5-tri (pyrrol-2-ly)benzene, respectively. Interestingly, both CMPs showed very high catalytic activity toward Knoevenagel condensation reaction, which was attributed to the inherent pore channels, high specific surface areas and abundant nitrogen sites within CMPs. Additionally, both CMPs displayed excellent recyclability with negligible degradation after 10 cycles. This work provides new possibilities into designing novel nitrogen-rich high-performance heterogeneous catalysts.

Transition Metal-Free N-Arylation of Amino Acid Esters with Diaryliodonium Salts

A transition metal-free approach for the N-arylation of amino acid derivatives has been developed. Key to this method is the use of unsymmetric diaryliodonium salts with anisyl ligands, which proved important to obtain high chemoselectivity and yields. The scope includes the transfer of both electron deficient, electron rich and sterically hindered aryl groups with a variety of different functional groups. Furthermore, a cyclic diaryliodonium salt was successfully employed in the arylation. The N-arylated products were obtained with retained enantiomeric excess.

Structure determination, correction, and disproof of marine macrolide natural products by chemical synthesis

Integration of chemical synthesis, NMR spectroscopy, and various analytical means is key to success in the structure elucidation of stereochemically complex marine macrolide natural products.

Manipulating Solid Forms of Contact Insecticides for Infectious Disease Prevention

Malaria control is under threat by the development of vector resistance to pyrethroids in long-lasting insecticidal nets, which has prompted calls for a return to the notorious crystalline contact insecticide DDT. A faster acting difluoro congener, DFDT, was developed in Germany during World War II, but in 1945 Allied inspectors dismissed its superior performance and reduced toxicity to mammals. It vanished from public health considerations. Herein, we report the discovery of amorphous and crystalline forms of DFDT and a mono-fluorinated chiral congener, MFDT. These solid forms were evaluated against Drosophila as well as Anopheles and Aedes mosquitoes, the former identified as disease vectors for malaria and the latter for Zika, yellow fever, dengue, and chikungunya. Contact insecticides are transmitted to the insect when its feet contact the solid surface of the insecticide, resulting in absorption of the active agent. Crystalline DFDT and MFDT were much faster killers than DDT, and their amorphous forms were even faster. The speed of action (a.k.a. knockdown time), which is critical to mitigating vector resistance, depends inversely on the thermodynamic stability of the solid form. Furthermore, one enantiomer of the chiral MFDT exhibits faster knockdown speeds than the other, demonstrating chiral discrimination during the uptake of the insecticide or when binding at the sodium channel, the presumed destination of the neurotoxin. These observations demonstrate an unambiguous link between thermodynamic stability and knockdown time for important disease vectors, suggesting that manipulation of the solid-state chemistry of contact insecticides, demonstrated here for DFDT and MFDT, is a viable strategy for mitigating insect-borne diseases, with an accompanying benefit of reducing environmental impact.

Catalytic Enantioselective Addition of an Allyl Group to Ketones Containing a Tri-, a Di-, or a Monohalomethyl Moiety. Stereochemical Control Based on Distinctive Electronic and Steric Attributes of C-Cl, C-Br, and C-F Bonds

We disclose the results of an investigation designed to generate insight regarding the differences in the electronic and steric attributes of C-F, C-Cl, and C-Br bonds. Mechanistic insight has been gleaned by analysis of variations in enantioselectivity, regarding the ability of electrostatic contact between a halomethyl moiety and a catalyst's ammonium group as opposed to factors lowering steric repulsion and/or dipole minimization. In the process, catalytic and enantioselective methods have been developed for transforming a wide range of trihalomethyl (halogen = Cl or Br), dihalomethyl, or monohalomethyl (halogen = F, Cl, or Br) ketones to the corresponding tertiary homoallylic alcohols. By exploiting electrostatic attraction between a halomethyl moiety and the catalyst's ammonium moiety and steric factors, high enantioselectivity was attained in many instances. Reactions can be performed with 0.5-5.0 mol % of an in situ generated boryl-ammonium catalyst, affording products in 42-99% yield and up to >99:1 enantiomeric ratio. Not only are there no existing protocols for accessing the great majority of the resulting products enantioselectively but also in some cases there are hardly any instances of a catalytic enantioselective addition of a carbon-based nucleophile (e.g., one enzyme-catalyzed aldol addition involving trichloromethyl ketones, and none with dichloromethyl, tribromomethyl, or dibromomethyl ketones). The approach is scalable and offers an expeditious route to the enantioselective synthesis of versatile and otherwise difficult to access aldehydes that bear an α-halo-substituted quaternary carbon stereogenic center as well as an assortment of 2,2-disubstituted epoxides that contain an easily modifiable alkene. Tertiary homoallylic alcohols containing a triazole and a halomethyl moiety, structural units relevant to drug development, may also be accessed efficiently with exceptional enantioselectivity.

Asymmetric transfer hydrogenation of seven membered tricyclic ketones: N-substituted dibenzo[b,e]azepine-6,11-dione driven by nonclassical CH/O interactions

Enantioselective transfer hydrogenation of dibenzo-fused-azepine-diones: N-substituted dibenzo[b,e]azepin-6-11-dione was achieved by ruthenium catalysis in the presence of formic acid/triethylamine as a mild hydrogen source.

Synthesis of 1- and 4-substituted piperazin-2-ones via Jocic-type reactions with N-substituted diamines

Enantiomerically-enriched trichloromethyl-containing alcohols are transformed regioselectively into enantiomerically-enriched 1-substituted piperazinones by modified Jocic reactions.