• N-mesyl aziridines
• stereoselective synthesis
• vinyl oxiranes

Multisubstituted 2,5-dihydropyrroles and 2,5-dihydrofurans are recognized as valuable heterocyclic systems because they could be advantageously used as starting materials for the preparation of many pharmaceutically relevant compounds. The possibility of the construction of an enantiomerically pure cis-2,5-disubstituted-2,5-dihydropyrrole and cis-2,5disubstituted-2,5-dihydrofuran systems respectively starting from glycal-derived vinyl N-mesyl aziridines and oxiranes, when subjected to appropriate reaction conditions, was examined.
The reaction of N-mesyl aziridines and oxiranes with metal enolates derived from active methylene compounds afforded, through a rearrangement process implying an opening-closing process with contemporary ring contraction of the initially obtained 1,4-addition product (primary reaction product), the corresponding cis-2,5-disubstituted-2,5-dihydropyrrole and cis-2,5-disubstituted-2,5-dihydrofuran (both secondary reaction products), respectively, in a completely region- and stereoselective fashion.