A synthesis of trifluoromethyl-substituted naphthalenes

Alkyl and aryl Grignard reagents add to 1-(3,4-dihydro-2H-5-pyranyl)-2,2,2-trifluoro-1-ethanone by 1,4-addition, but benzyl Grignard reagents react in good yield by 1,2-addition. Dehydration of the resulting alcohols affords intermediate dienes, which readily undergo cyclisation to give substituted trifluoromethylnaphthalenes. Addition to other trifluoromethylketones permits access to a range of novel fluorinated naphthalenes and benzenes.