Base-Promoted Transannulation of Heterocyclic Enamines and 2,3-Epoxypropan-1-ones: Regio- and Stereoselective Synthesis of Fused Pyridines and Pyrroles

An efficient domino strategy for synthesis of 3-substituted 4-oxo-4,5-dihydro-1H-pyrrolo[3,2-c]pyridine derivatives in water

A strategy for catalyst-free domino reaction of 4-aminopyridin-2(1H)-ones, arylglyoxal hydrates and different 1,3-dicarbonyl compounds in water has been established. The mild and efficient procedure afforded pyrrolo[3,2-c]pyridine derivatives with 76-94% yields after simple crystallization. The present procedure shows promising characteristics, such as readily available starting materials, the use of water as reaction media, simple and efficient one-pot operation, and avoiding the need for any hazardous or expensive catalysts.

Synthesis of Diastereoenriched α-Aminomethyl Enaminones via a Brønsted Acid-Catalyzed Asymmetric aza-Baylis-Hillman Reaction of Chiral N-Phosphonyl Imines

An effective chiral GAP methodology for preparing α-aminomethyl enaminones through a (R)-CSA-catalyzed asymmetric aza-Baylis-Hillman reaction is reported. Excellent yields and high diastereoselectivity could be obtained under mild conditions and convenient GAP techniques. The confirmations of the absolute configuration of N-phosphonyl imine and chiral enaminone by X-ray diffraction provides an explicit explanation of the chirality mechanism for GAP chemistry.

Synthesis of new tetronamides displaying inhibitory activity against bloom-forming cyanobacteria

BACKGROUND

The increasing frequency and intensity of cyanobacterial blooms pose a serious threat to aquatic ecosystems. These blooms produce potent toxins that can contaminate drinking water and endanger the life of wild and domestic animals as well as humans. Consequently, the development of effective methods for their control is a matter of high priority. We have previously shown that some γ-benzylidenebutenolides, related to the rubrolide family of natural products, are capable of inhibiting the photosynthetic electron transport chain (Hill reaction), a target of commercial herbicides. Here we report the synthesis and biological properties of a new class of rubrolide-inspired molecules featuring a tetronamide motif.

RESULTS

A total of 47 N-aryl tetronamides, including 38 aldol adducts, were prepared bearing phenyl, biphenyl, naphthyl, aliphatic and heteroaromatic groups. Some of the aldol adducts were dehydrated to the corresponding γ-benzylidenetetronamides, although satisfactory yields were obtained in only three cases (52-97%). None of the synthesized compounds were capable of blocking the Hill reaction. This notwithstanding, several aldol adducts equipped with a biphenyl substituent displayed excellent inhibitory activity against Synechococcus elongatus and other cyanobacterial strains (IC₅₀  = 1-5 μM). Further, these tetronamides were found to be essentially inactive against eukaryotic microorganisms.

CONCLUSION

Several newly synthesized biphenyl-containing tetronamides were shown to display potent and selective inhibitory activity against cyanobacteria. These compounds appear to exert their biological effects without interfering with the Hill reaction. As such, they represent novel leads in the search of environmentally benign agents for controlling cyanobacterial blooms. © 2019 Society of Chemical Industry.

tert-Butyl peroxide (TBHP)/KI-mediated dual C(sp2)-H bond amination of arylamines with α-diazo carbonyls toward 1,2,4-benzotriazines

A new radical-induced dehydrogenative heterocyclization of arylamines with α-diazo carbonyls has been established under metal-free oxidative conditions, enabling two-fold C(sp2)-H bond amination to access a wide range of functionalized 1,2,4-triazine derivatives with generally good yields by combining KI/tert-butyl peroxide (TBHP). The present protocol features wide substrate scope, commercial accessibility, and mild reaction conditions. Mechanistic details of this radical process are rendered by conducting systematic theoretical calculations.

Iodine–NH4OAc mediated regioselective synthesis of 2-aroyl-3-arylimidazo[1,2-a]pyridines from 1,3-diaryl-prop-2-en-1-ones

An efficient, metal-free regioselective synthesis of 2-aroyl-3-arylimidazo[1,2-a]pyridines from 1,3-diaryl-prop-2-en-1-ones has been developed by their reaction with 2-aminopyridine in the presence of I₂/NH₄OAc.

Thermodynamically driven, syn-selective vinylogous aldol reaction of tetronamides

A stereoselective vinylogous aldol reaction of N-monosubstituted tetronamides with aldehydes is described.

Synthesis of 3-Iminoindol-2-amines and Cyclic Enaminones via Palladium-Catalyzed Isocyanide Insertion-Cyclization

A palladium-catalyzed isocyanide insertion-cyclization using low-cost and readily accessible 2-haloanilines, 2-iodophenylethanones, and isocyanides for efficient synthesis of 3-iminoindol-2-amine and cyclic enaminone derivatives has been developed. The method features low-cost and readily accessible starting materials, reliable scalability, and bond-forming efficiency as well as simple one-pot operation, which makes this strategy highly attractive. A reasonable mechanism for forming 3-iminoindol-2-amine involved double isocyanide insertion/cyclization process is proposed.