Asymmetric Organocatalytic Cyclopropanation of Enals

Significance

A highly chemo- and enantioselective organocatalytic cyclopropanation of α,β-unsaturated aldehydes with bromomalonates and 2-bromo acetoacetate has been developed. Pyrrolidine catalyst 1 in combination with Et₃N has been found to be effective for this reaction. The reaction proceeds through both iminium and enamine catalysis. With 20 mol% of catalyst 1, moderate to good yields (50-88%) and high enantioselectivities (er = 97:3 to 99.5:0.5) were obtained for different β -substituted enals. In the case of 2-bromo acetoacetate the products were obtained in 3:1 ratio with high enantioselectivity (er = 97:3).