Highly Enantio- and Diastereoselective Synthesis of 1,2,3-Trisubstituted Cyclopropanes from α,β-Unsaturated Amides and Stabilized Sulfur Ylides Catalyzed by a Chiral Copper(I) Complex

The
stereoselective preparation of 1,2,3-substituted cyclopropanes
from α,β-unsaturated carbonyl compounds in the carboxylic
acid oxidation state through Michael addition-initiated ring-closure
reactions is a significant challenge in organic synthesis. Herein,
the previously elusive catalytic asymmetric cyclopropanation of α,β-unsaturated
amides with stabilized sulfur ylides has been efficiently accomplished
utilizing a chiral Cu­(I) complex. This Lewis acid catalytic system
effectively converts a wide range of electron-deficient alkenes into
the corresponding 1,2,3-trisubstituted cyclopropanes under mild reaction
conditions in good to excellent yields with both high to excellent
enantio- and diastereoselectivities. The resulting enantiomerically
enriched cyclopropane amides can be readily diversified into promising
synthetic intermediates such as β-aminocyclopropanecarboxylic
acids with the facile recovery of the 7-azaindoline auxiliary without
influencing the optical purity of the cyclopropane unit, which highlights
the synthetic efficacy of this catalytic approach.