• dihydropyrrole
• rearrangement process
• regio- and stereoselectivity
• vinyl aziridines

Multisubstituted 2,5-dihydropyrroles are recognized as valuable heterocycles 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 system starting from D-allal and D-galactal-derived vinyl N-mesyl aziridines, when subjected to appropriate reaction conditions, was examined.
The reaction of N-mesyl aziridines with metal enolates derived from active methylene compounds, as dimethyl malonate and dibenzoyl methane, 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 (the secondary reaction product) in a completely regio- and stereoselective fashion.
Subsequently, the possibility of substituting the N-mesyl group of aziridine with an easily removable protecting-activating-group was checked in the same rearrangement process.
In this framework N-nosyl group turned out to be sufficiently efficient for the rearrangement process to 2,5-dihydropyrroles and easy to be removed by the simple PhSH/K2CO3 protocol to give corresponding 2,5-dihydropyrroles bearing the free NH group.
Preliminary studies were also carried out on the new N-Cbz and N-TFA substituted aziridines in order to check the possibility of using these alternative N-protections in glycosylation reactions of alcohols taken as a simple and appropriate model reaction.