Treatment of δ-alkenylamines (1a-1d) with a catalytic amount of butyllithium gave cis-N-methyl-2,5-disubstituted pyrrolidines (2a-2d) stereoselectively in good yields.
Treatment of 4- and 5-alkynylamines with 0.5-1.2 equiv. of butyllithium brought about a facile anionic cyclization, giving the corresponding enamine pyrrolidines and piperidines having an exo double bond in high yields. Treatment of 4-alkynamides with lithium aluminum hydride also gave the similar enamine pyrrolidines in high yields.
New facile synthesis of substituted 2-benzylidene-pyrrolidines by the anionic cyclization of δ-alkynylamines