CARBOINDATION OF ALKYNES - REGIOSELECTIVE AND STEREOSELECTIVE ALLYLATION OF CARBON-CARBON TRIPLE BONDS OF ALKYNOLS BY ALLYLIC INDIUM REAGENTS

Allylindium sesquihalides undergo smooth allylindation with terminal alkynes bearing a neighboring hydroxyl group at 100-140 degrees C to give allylalkenols. The coupling occurred regioselectively at the gamma-carbon of the allylindium reagents via syn-addition, whereas the regioselectivity concerning the alkynol depends upon the structures of both allylindium and alkynol. The allylation of nonfunctionalized alkynes is less efficient, requiring higher reaction temperature (150-180 degrees C) and giving lower yields. Mechanistic considerations suggest a hydroxyl-assisted concerted process for the allylindation of alkynols, whereas a radical pathway is more likely for nonfunctionalized alkynes. Three monoterpene alcohols, i.e., yomogi alcohol, achillenol, and isomyrcenol, were conveniently prepared via allylindation of appropriate alkynols.