Highly Enantiomerically Enriched Ketone Homoenolate Reagents Prepared by (-)-Sparteine-Mediated γ-Deprotonation of Achiral 1-Alkenyl Carbamates

摘要

Enantiomerically enriched, 1-hetero-substituted 2-alkenylmetal compounds 1 (e.g., M=Li, Ti(OiPr)_3, Ti(NEt_2)_3) are powerful homoenolate reagents. They react with aldehydes and ketones with virtually complete 1,3-transfer of chirality to form optically active homoaldol products 2(Scheme 1). In the best homoenolate reagents 1 the substituent X is a complexing N,N-dialkylcarbamoyloxy group or a tert-butoxycarbonylamino group, both of which enhance the kinetic acidity in the deprotonation of the allylic precursor and are able to hold the counterion in compound 1 at the α-position.