One-pot synthesis of difluoromethyl-containing 1,2,3,4-tetrahydropyridines

Difluoromethyl-containing diethyl 1,2,3,4-tetrahydropyridine-3,5-dicarboxylate derivatives were synthesized in up to 90% yields by the Mannich reaction of ethyl 4,4-difluoroacetoacetate with formaldehyde and primary amine hydrochlorides. The effects of the reactant structure and reaction conditionson the efficiency of formation of 1,2,3,4-tetrahydropyridines and hexahydropyrimidines was studied. In the presence of NaCl in an acetate buffer (рН 4), the 1,2,3,4-tetrahydropyridine structure is formed selectively. When 4-aminophenol hydrochloride is used, the 3,4,5,6-tetrahydropyrimidin-1-ium difluoroacetate salt is produced, apart from the target product. The reactions with (S)-α-amino acid ester hydrochlorides afford mixtures of two diastereomeric 1,2,3,4-tetrahydropyridines.