Asymmetric 1,2-Carbamoyl Rearrangement of Lithiated Chiral Oxazolidine Carbamates and Diastereoselective Synthesis of α-Hydroxy Amides

Asymmetric 1,2-carbamoyl rearrangement of lithiated 2-alkenyl carbamates has been investigated. Deprotonation of chiral 2-alkenyl oxazolidine carbamates with sec-butyllithium in ether at -78 °C followed by warming of the resulting 1-lithio-2-alkenyl derivatives to room temperature resulted in 1,2-carbamoyl rearrangement to provide α-hydroxy amides. The rearrangement proceeded with excellent diastereoselectivity and in good to excellent isolated yield of the α-hydroxy amide derivatives. The substrate scope of the reaction was investigated with a variety of 2-alkenyl and benzyl oxazolidine carbamates. A stereochemical model is provided to explain the stereochemical outcome associated with the rearrangement. Acid-catalyzed removal of the chiral oxazolidine afforded α-hydroxy acid in high optical purity.