Asymmetric [3,3]- and [1,3]-Sigmatropic Rearrangements of γ-Allyloxy Vinylogous Urethanes

Vinylogous urethanes derived from condensation of prolinol or prolinol <i>tert</i>-butyldimethylsilyl ether with 4-allyloxyketoester were found to undergo a thermal [3,3]-sigmatropic rearrangement, providing compounds with N-substituted quaternary carbon centers. Cyclizations (subsequently or in situ) of the rearranged products generated hexahydro-3,4-dioxa-8a-aza-as-indacen-2-ones. Various terminally substituted allyloxy ketoesters and arylmethoxy ketoesters were found to generate tricyclic compounds via [1,3]-sigmatropic rearrangement. Finally, tricyclic lactones were transformed successfully into lactams.