Chemistry of Hantzsch cyclization: stereochemistry of the 2-hydroxy-1,2,3,4-tetrahydropyridine intermediate of Hantzsch cyclization. X-Ray molecular structure of diastereoisomers of 5-(2-cyanoethyl) 3-methyl 2-dimethoxymethyl-2-hydroxy-6-methyl-4-(3-nitrophenyl)-1,2,3,4-tetrahydropyridine-3,5-dicarboxylates
Abstract
Hantzsch cyclization of cyanoethyl 3-aminocrotonate and (E,Z)-4,4-dialkoxy-2-benzylideneacetoacetates 12a–h afforded the corresponding 3,4-trans-2-hydroxy-1,2,3,4-tetrahydropyridines 14a–h with high stereoselectivity. 1H NMR and X-ray analyses of compound 14a established the configuration of 3-H and 4-H as trans and that of 3-H and 2-OH as trans also.