Synthesis of trifluoromethylnaphthalenes

Reaction of 1-(3,4-dihydro-2H-5-pyranyl)-2,2,2-trifluoro-1-ethanone with benzylic Grignard reagents affords by 1,2-addition unsaturated allylic alcohols. These alcohols readily undergo dehydration and cyclisation to give trifluoromethylnaphthalenes. The generality of this procedure was established by reaction with diverse benzyl and allyl Grignard reagents and by reaction of a number of unsaturated ketones. The resulting trifluoromethylnaphthalenes were oxidised to give substituted acetic- and propionic acids. (C) 2000 Elsevier Science Ltd. All rights reserved.