Organocatalytic Asymmetric Synthesis of α-Chloroesters

Significance

A novel organocatalytic asymmetric method to synthesize α-substituted esters has been established. 2,2-Dichloroaldehydes are treated with a mixture of a phenol derivative, potassium hydride, 18-crown-6, and 20 mol% of a chiral triazolium salt to provide α-chloroesters in good yields and enantioselectivities. The reaction presumably proceeds via an asymmetric protonation of a chiral α-haloenolate. Due to the tolerance of diverse functional groups including olefins, ethers, and esters, a variety of aldehydes can be utilized. An example of an α-chlorinated ester is demonstrated to be transformed into the corresponding acid and alcohol with retention as well as to an α-azidoester with inversion of the configuration.