Abstract
In the presence of a chiral promoter consisting of tin(II) triflate, a chiral diamine, and tributylin fluoride, the silyl enol ether of S-ethyl ethanethioate or S-tert-butyl ethanetioate reacts with aldehydes to afford the corresponding aldol-type adducts in good yields with high enantioselectivities. In the reaction of silyl enol ether of S-ethyl propanethioate with aldehydes, perfect stereochemical control is attained by the combined use of tin(II) triflate, a chiral diamine, and dibutylin diacetate. A wide variety of aldehydes, including aliphatic, α,β-unsaturated, and aromatic aldehydes, are applicable to this reaction. The chiral promoters are characterized by 119 Sn NMR spectra and proved to form the three-component complexes, which behave as chiral Lewis acids. The reaction proceeds directly from silyl enol ethers without any accompanying metal exchange on the enolates
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