REGIOAPLYRONINE AND STEREOC SYNTHESIS OF SILYL ENOL ETHERS USING A NEW BASE ELECTROGENERATED FROM HEXAMETHYLDISILAZANE

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.