Acylation of Nitronates: [3,3]-Sigmatropic Rearrangement of in Situ Generated N‑Acyloxy,N‑oxyenamines

Acylation of nitronates affords α-acyloxyoxime derivatives via an umpolung functionalization of the α-position. This transformation involves generation of hitherto unknown N-acyloxy,N-oxyenamines and their fast [3,3]-sigmatropic rearrangement driven by the cleavage of the weak N–O bond. The reaction has a broad scope, and it is regioselective in the case of nitronates possessing nonsymmetrically substituted α-positions. Application to the formal total synthesis of clausenamide and cis-clausenamide is presented.