Asymmetric Petasis-Type Reaction Catalyzed by a New Bifunctional Thiourea

Significance

A new bifunctional organocatalyst for an asymmetric Petasis-type reaction has been designed. Chiral thiourea 1 mediates the regio­selective 1,2-addition of boronic acids 3 to N-acylated quinolinium salts generated in situ from the corresponding quinolines 2 and phenyl chloro­formate to give dihydroquinolines 4 in moderate yields and high enantioselectivities. Moreover, a possible mode of dual activation is provided. While the thiourea moiety (Brønsted acid) is coordinated by the carbonyl group of the quinolinium ion to control the s-trans/s-cis conformation, the 1,2-amino alcohol functionality (Lewis base) chelates the boronic acid to increase the nucleophilicity.