β-Oxidation of Ynamides into <i>N</i>,<i>O-</i>Acetals by <i>m</i>CPBA: Application in Enantioselective Intermolecular Transacetalization

Abstract

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.