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.
Intramolecular PIFA-Mediated Alkyne Amidation and Carboxylation Reaction
The hypervalent iodine reagent PIFA promotes the intramolecular electrophilic cyclization of easily accessible alkynylamides and alkynyl carboxylicacids, leading to the formation of pyrrolidinone and lactone skeletons, respectively, in a very efficient way. A synthetic study and a mechanistic proposal for these transformations are presented.