Synthesis of highly substituted cyclobutane fused-ring systems from N-vinyl beta-lactams through a one-pot domino process.

In this contribution, aminocyclobutanes, as well as eight-membered enamide rings, have been made from N-vinyl beta-lactams. The eight-membered products have been formed by a [3,3]-sigmatropic rearrangement, whereas the aminocyclobutanes have been derived from a domino [3,3]-rearrangement/6pi-electrocyclisation process. The aminocyclobutanes have been obtained in a highly diastereoselective fashion. The cyclobutane ring system tolerates fusion even if adjacent quaternary centres are present. Systems containing up to four fused rings are readily accessible. The reaction profile has been investigated by using Gaussian 03. This study suggests that two reaction pathways for aminocyclobutane formation are possible. In one pathway the [3,3]-sigmatropic rearrangement is the rate-limiting step and in the second pathway the electrocyclisation is rate limiting. Taken together, these reactions should facilitate the construction of fused heterocycles.