CHROMIUM(II)-MEDIATED STEREODIVERGENT ADDITIONS OF ALLYLIC PHOSPHATES AND HALIDES TO ALDEHYDES

The addition of gamma-disubstituted allylchromium(III) reagents to aldehydes proceeds in a stereodivergent manner, in contrast to the case of gamma-monosubstituted allylchromium(III) species. The method allows the preparation of a variety of homoallylic alcohols bearing a quaternary center of defined relative configuration in the alpha-position. The preparation of both stereomeric homoallylic alcohols 13 is possible by using either of the two (E)- or (Z)-allylic precursors. The reaction has been extended to a gamma-monosubstituted beta-(trimethylsilyl)allylic system. The intermediate allylic chromium(III) reagents can be conveniently prepared from the corresponding phosphates (or chlorides) in DMPU or THF in the presence of catalytic amounts of LiI.