Rhodium/diene-catalyzed asymmetric arylation of N-Boc-protected α,β-unsaturated δ-lactam with arylboronic acids: enantioselective synthesis of 4-aryl-2-piperidinones

Utilizing toluene/isopropanol (20:1 to 40:1) as a solvent and KHF2 as an additive, the rhodium/diene-catalyzed asymmetric arylation (RCAA) reaction of arylboronic acids to N-Boc-protected α,β-unsaturated δ-lactam proceeded smoothly to afford chiral 4-aryl-2-piperidinones with high to excellent yields (up to 94%) and enantioselectivities (up to >99% ee). Further conversion of adduct (R)-1-(tert-butyloxycarbonyl)-4-(4-chlorophenyl)-2-piperidone to (R)-Homobaclofen hydrochloride was also presented.