D. Bonafoux et al., REGIOAPLYRONINE AND STEREOC SYNTHESIS OF SILYL ENOL ETHERS USING A NEW BASE ELECTROGENERATED FROM HEXAMETHYLDISILAZANE, Journal of organic chemistry, 61(16), 1996, pp. 5532-5536
The hexamethyldisilazane magnesium salt, a new base readily electrogen
erated in an undivided cell fitted with a sacrificial magnesium anode,
using a normally equilibrating medium (DME/15% vol HMPA mixture), exh
ibited a surprising regioselectivity leading to the less highly substi
tuted silyl enol ethers from unsymmetrical ketones. This regioselectiv
ity was not temperature dependent, but was strongly dependent on the n
ature and proportions of the solvent/cosolvent mixture. Moreover, the
reaction was different in pure NMP, and exclusively afforded, from 2-p
entanone, the new silylated aldol (56% yield) which resulted from the
condensation of the less highly substituted enolate with the ketone.