Cyclobutenes from 1-alkyl-1,4-dihydropyridines with dimethyl acetylenedicarboxylate and a novel cyclo-elimination of a carboxamide group
Abstract
Several 1,3-disubstituted-1,4-dihydropyridines with dimethyl acetylenedicarboxylate gave 1-azabicyclo-[4,2,0]octa-2,5-dienes, and where a 3-CO2H or a 3-CONHR group was present elimination of this group occurred through a 6-membered cyclic transition state in each case to give the corresponding 3-(cis-1,2-dimethoxycarbonylvinyl) derivative.