Enantioselective Conjugate Addition of Catalytically Generated Zinc Homoenolate

Abstract

We report herein an enantioselective conjugate addition reaction of a zinc homoenolate, catalytically generated via ring opening of a cyclopropanol, to an alpha,beta-unsaturated ketone. The reaction is promoted by a zinc aminoalkoxide catalyst generated from Et2Zn and a chiral beta-amino alcohol to afford 1,6-diketones, which undergo, upon heating, intramolecular aldol condensation to furnish highly substituted cyclopentene derivatives with good to high enantioselectivities. The reaction has proved applicable to various 1-substituted cyclopropanols as well as chalcones and related enones. The chiral amino alcohol has proved to enable ligand-accelerated catalysis of the homoenolate generation and its conjugate addition. Positive nonlinear effects and lower reactivity of a racemic catalyst have been observed, which can be attributed to a stable and inactive heterochiral zinc aminoalkoxide dimer.

Publication
Sekiguchi, Y.; Yoshikai, N. J. Am. Chem. Soc. 2021, 143, 4775-4781.