1,2-Carbamoyl Migration on Enantio-enriched (alpha)-Lithioalkyl Carbamates Generated with s-Butyllithium/Sparteine: Steric Course and Mechanism

Alkyl N,N-diisopropylcarbamates, when lithiated with sBuLi/(-)-sparteine in ether at -78 °C followed by warming to room temperature, are shown to undergo the 1,2-carbamoyl migration to give the (alpha)-hydroxy amides in >95% ee with complete retention of configuration at the Li-bearing carbanion terminus. An addition-elimination mechanism is proposed.