Three‐ and Seven‐membered Annulenones as a Lewis Base Catalyst for Enantioselective meso‐Epoxide Opening

This is the report on the Lewis base catalysis of annulenones. Additionally, the synthesis of chiral annulenone catalysts and their application in asymmetric ring‐opening reactions of meso‐epoxides is shown. Annulenones, such as cyclopropenones and tropones, function as Lewis bases owing to their inherent polarity caused by aromaticity, resulting in the activation of silicon tetrachloride, which catalyzes the ring‐opening reaction of meso‐epoxides. Moreover, various chiral annulenone catalysts have been designed and synthesized, and microwave irradiation has been shown to improve the synthetic efficiency of chiral tropones. The chiral annulenones successfully catalyzed the asymmetric ring‐opening reaction of meso‐epoxides, resulting in the formation of 1,2‐chlorohydrins in a high yield and high enantioselectivity (up to 90% ee in 96% yield). These results represent the example of three‐ and seven‐membered annulenones as a chiral Lewis base catalyst.