Diastereoselective Cyclization of N‐Alkenylideneamines into 3,4‐Dihydro‐2H‐pyrrol‐1‐ium Halides.

Abstract

Diastereoselective Cyclization of N-Alkenylideneamines into 3,4-Dihydro--2H-pyrrol-1-ium Halides. -Novel approaches towards the diastereoselective electrophile-induced cyclization of N-alkenylidene alkylamines are presented. The halocyclization of chiral N-alkenylidene alkylamines (I) proceeds with only low to moderate diastereoselectivity. Similar results are achieved with the selenocyclization of related N-alkenylidene alkylamines (V), and the introduction of additional prochiral substituents into the imines does not give improved stereoselectivities. Diastereoselectivities of up to 68% d.e. are achieved when a chiral imine (XII) is reacted with a chiral selenium bromide (XV) as well as by application of N-alkenylidene alkylamines bearing stereocenters at the alkenylidene chain (XVII). -(SCHLEY, D.; LIEBSCHER*, J.; Eur.