Abstract
Deprotonation of a (−)-quinic acid-derived ketone {(2 S,3 S,4a R,8 R,8a S)-8-[( tert-butyl(dimethyl)silyl)oxy]-2,3-dimethoxy-2,3-dimethylhexahydro-1,4-benzodioxin-6(5 H)-one} using lithium hexamethyldisilazide (LHMDS) at −78 °C gave one regioisomeric enolate. The regiocontrol is governed by the axial β-silyloxy substituent and the resulting lithium enolate is stable towards β-elimination at temperatures up to −40 °C. It was found that the axial β-silyloxy group could be conveniently eliminated using 2.1 equiv of LHMDS at 0 °C for 1 h and that an equatorial β-alkoxy group was much more resistant to β-elimination. A chiral lithium amide base was used to overturn the inherent regioselectivity of ketone deprotonation with LHMDS.
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