Asymmetric dihydroxylation of vinyl- and allyl-silanes

Abstract

Allyl- and vinyl-silanes undergo efficient dihydroxylation using the Sharpless AD-mix-α and β-reagents. Thirteen examples are given. The chemical yields were typically 80% or more, but the enantiomeric excesses (ee) are critically dependent on the structure of the alkene. The ee values obtained were greater than 96% for E-allyl- and vinyl-silanes but only 50–60% for the Z-analogues, and less than 30% for the parent allyl- and vinyl-silanes. A disubstituted vinylsilane required forcing conditions for reaction and gave an ee of 85%. The dihydroxy compounds from allylsilanes can be converted stereoselectively into chiral allyl alcohols. The vinylsilane-derived diols were readily converted into aldehydes by a Peterson reaction, and with a trace of acid acetals are recovered in high yield. For 1-trimethylsilyl-ethane-1,2-diol the cyclic sulfate was made in good yield and gave the 2-silyl-substituted aziridine with PhNH₂ and BuLi.