One-pot pseudo three-component reaction of nitroketene-N,S-acetals and aldehydes for synthesis of highly functionalized hexa-substituted 1,4-dihydropyridines
We have described the simple, convenient and high yielding one-pot synthesis of a library of highly functionalized hexa-substituted 1,4-dihydropyridines (1,4-DHPs) by 2-aminopyridine catalysed pseudo three-component reaction of nitroketene-N,S-acetals and aldehydes. This domino transformation involves formation of dihydropyridine ring by creation of two C–C bonds and one C–N bond, all of them taking place in a single synthetic operation. As the products precipitate out of the reaction simple filtration is enough to gather the products and thus, there is no need for work-up or column-chromatography. The C6-methylsulfanyl group in the product 1,4-DHPs was substituted with primary and secondary amines to provide 1,4-DHPs with further possibilities in structural diversity. As a demonstration of application of the method we have synthesised an analogue of nitenpyram, a neonicotinoid insecticide.