T. Takagi et al., A METHOD FOR SYNTHESIS OF FLUORINE-COMPOUNDS USING ABNORMAL GRIGNARD REACTION OF HALOTHANE .3. SIMPLE SYNTHESIS OF TRIFLUOROMETHYLCHLOROOLEFINS, Chemical and Pharmaceutical Bulletin, 44(2), 1996, pp. 280-283
We have reported an abnormal Grignard reaction of halothane (1) with c
arbonyl compounds (2). The reaction afforded 1-bromo-1-chloro-2,2,2-tr
ifluoroethylcarbinols (3) as the major products at -53 degrees C, whil
e at 0 degrees C, the main products were the dehalogenation products,
1-chloro-2,2-difluoroethenyl carbinols (4). Treatment of 4 with hydrog
en fluoride (HF) afforded 1-chloro-1-(trifluoromethyl)ethene derivativ
es (5) in good yields. However, this reaction required HF, a dangerous
reagent. Here, we describe a much easier and safer synthesis of 5. Th
us, treatment of 3 with zinc chloride and acetic anhydride gave acetox
y compounds (6). The acetates were converted to the olefins (5) by red
uctive debromoacetoxylation with zinc in the presence of a catalytic a
mount of copper(I) iodide. Application of this reaction to an alpha,be
ta-unsaturated ketone, benzalacetone, gave the diene bearing a trifluo
romethyl group.