Asymmetric conjugate addition of bromonitromethane to cyclic enones catalyzed by chiral monosulfonated diamines

A series of chiral monosulfonated diamines were prepared and used as the catalysts for asymmetric conjugate addition of bromonitromethane to alpha,beta-unsaturated ketones. The reaction provided nitrocyclopropanes in the presence of appropriate acid and base additives. 1,3,5-Triisopropylbenzenesulfonated 1,2-diphenylethane-1,2-diamine was found to be the best catalyst. The reaction of cyclohex-2-enone and cyclohept-2-enone gave the nitrocyclopropanes in excellent enantioselectivities and yields. Moderate enantioselectivities were obtained for cyclopent-2-enone. The hydrogen-bonding interaction between N-H bonds of sulfonamides and bromonitromethane is suggested to be important for the catalytic activity and enantioselectivity.