Recent Developments in the Enantioselective Syntheses of Cyclopropanes

A new type of chiral vinylcarbene equivalent used by S. Hanessian et al. is the optically active chloroallylphosphonic acid amide 1. After deprotonation it adds to α,β-unsaturated carbonyl compounds 2 (R = H, Me) to yield the highly functionalized cyclopropane derivatives 3 with a high degree of enantiomeric purity. The substitution pattern of the cyclopropane derivatives predestines them to be starting materials for many syntheses.