Selective Reduction of Organic Compounds with Al-Trifluoromethanesulfonyldiisobutylalane. Comparison of Its Reactivity with Al-Methanesulfonyldiisobutylalane

摘要

The new MPV type reagent, Al-trifluoromethanesulfonyldiisobutylalane (DIBAO3SCF3), has been prepared and its reducing characteristics in the reduction of selected organic compounds containing representative functional groups have been examined, and compared its reactivity with that of Al-methanesulfonyldiisobutylalane (DIBAO3SCH3) in order to understand the fluorine-substituent effect on its reactivity. In general, the reactivity of DIBAO3SCF3 appears to be much higher than that of DIBAO3SCH3, apparently due to the acidity increase by the electron-withdrawing fluorine-substituent. The reagent reduced aldehydes and ketones readily, but showed a perfect selectivity in the reduction of α,β-unsaturated aldehydes and ketones to produce the corresponding allylic alcohols in an absolutely 100% purity. In addition, the reagent achieved the regioselective cleavage of phenyl- or/and alkyl-substituted epoxides to the less substituted alcohols in a perfect regioselectivity. Moreover, the reagent also showed an high stereoselectivity in the reduction of substituted cycloalkanones to produce the thermodynamically more stable alcohol epimers exclusively.