The Lewis Base-Catalyzed Silylation of AlcoholsA Mechanistic Analysis

Reaction rates for
the base-catalyzed silylation of primary, secondary,
and tertiary alcohols depend strongly on the choice of solvent and
catalyst. The reactions are significantly faster in Lewis basic solvents
such as dimethylformamide (DMF) compared with those in chloroform
or dichloromethane (DCM). In DMF as the solvent, the reaction half-lives
for the conversion of structurally similar primary, secondary, and
tertiary alcohols vary in the ratio 404345:20232:1. The effects of
added Lewis base catalysts such as 4-N,N-dimethylaminopyridine (DMAP) or 4-pyrrolidinopyridine (PPY) are
much larger in apolar solvents than in DMF. The presence of an auxiliary
base such as triethylamine is required in order to drive the reaction
to full conversion.