2 research outputs found
Leaving Group Effects on the Selectivity of the Silylation of Alcohols: The Reactivity–Selectivity Principle Revisited
TBS
protection of primary alcohol naphthalen-1-ylmethanol (<b>4a</b>) and secondary alcohol 1-(naphthalen-1-yl)ethanol (<b>4b</b>) has been studied under various reaction conditions. The
primary/secondary selectivity is largest in the comparatively slow
Lewis base catalyzed silylation in apolar solvents and systematically
lower in DMF. Lowest selectivities (and fastest reaction rates) are
found for TBS triflate <b>1b</b>, where only minor effects of
solvent polarity or Lewis base catalysis can be observed
The Lewis Base-Catalyzed Silylation of AlcoholsA 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-<i>N</i>,<i>N</i>-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