Enantioselective Acyl Migration Reactions of Furanyl Carbonates with Chiral DMAP Derivatives

An efficient enantioselective acyl migration reaction of furanyl carbonates was developed to construct all-carbon quaternary stereogenic centers. In some cases, the reactions required only 0.05 mol% (minimum 500 ppm) of catalyst and showed a high turnover frequency value (TOF; 3640 h(-1)). Multigram-scale reactions (10 grams) also proceeded with high enantioselectivity (> 99:1 e.r.) in quantitative yield. The catalyst was robust and easily recovered in 98% yield. A wide range of functional groups were tolerated (15 examples, > 98% yield, up to > 99:1 e.r.), and a variety of optically active 3,3'-disubstituted benzofuranone derivatives, which are useful intermediates for the synthesis of natural products and pharmaceuticals, were efficiently obtained. Control experiments on the catalyst structure (e.g., catalyst 1 a vs. 1 a' and 1 a") and computational calculations revealed that both the catalytic activity and enantioselectivity should be enhanced by hydrogen bonding between catalyst and substrate. Moreover, this system was applied to the challenging gamma-selective acyl migration reaction of furanyl carbonates with high gamma-selectivity and high enantioselectivity (a:gamma=10:90, 95:5 e.r.).