Enantioselective Synthesis of trans-1-Alkyl-
2-Substituted Cyclopropanes

Significance

The asymmetric synthesis of trans-1-alkyl-2-substituted cyclopropanes has traditionally been based on the well-known Simmons-Smith ­cyclopropanation. However, a stoichio­metric amount of a chiral dioxaborolane is needed and efficient catalytic methods are very rare. The authors represent a catalytic asymmetric tandem conjugate addition-intramolecular enolate trapping reaction by using the Cu-TolBINAP complex. Reactions of various Grignard reagents to 4-Cl-α,β-unsaturated esters, thioesters, and ­ketones provide highly functionalized cyclopropanes in excellent yields and enantioselectivities.