High regio- and stereo-selective introduction of a trifluoromethyl gro
up in various unsaturated systems is described. The key step is the tr
eatment of 1,1-difluoro-1-alken-3-ols with (diethylamino)sulphur trifl
uoride (DAST) to give 1,1,1-trifluoro-2-alkenes.