β-Oxidation of Ynamides into N,O-Acetals by mCPBA: Application in Enantioselective Intermolecular Transacetalization.

Oxidation of ynamides by mCPBA led to β-oxygenation and resulted in formation of carbonyl compounds with α-N,O-acetal functionality. These N,O-acetals are formed in high yields and can be stored indefinitely at room temperature. Yet, they can be activated by a chiral Brønsted acid and underwent an enantioselective transacetalization into a α-N,O-acetal. Subsequent diastereoselective transformations occurred with exceptional selectivity according to Felkin-Anh model.