Reaction of trifluoromethyl ketones. V. Dehydration of trifluoromethylated homoallyl alcohols. Synthesis of trifluoromethylated dienes.

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Abstract
1-(Trifluoromethyl)homoallyl alcohols, which were obtained by the ene reaction of trifluoromethyl ketones with olefins, were dehydrated with POCl3-pyridine or other acyl halide-organic base mixtures to trifluoromethylated dienes. Dehydration of the homoallyl alcohols from hexafluoroacetone afforded only one kind of products, while those from other trifluoromethyl ketones were dehydrated to the E-isomers of conjugated dienes as major products with small amounts of regio- and stereoisomers. Treatment of the homoallyl alcohols from inner olefins with phosphorus oxychloride in pyridine gave the conjugated dienes stereoselectively. The saturated (trifluoromethyl)-carbinols which were obtained by hydrogenation of trifluoromethylated homoallyl alcohols were very difficult to dehydrate. This fact shows that the formation of a conjugated double bond or the presence of an allylic hydrogen facilitates the dehydration.

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