Syntheses of 9-(Trifluoromethyl)- and 10-(Trifluoromethyl)-7,12-dimethylbenzanthracenes

Article abstract of DOI:10.1021/jo00167a018

4,4-Dimethyl-2-(2-lithio-4-(trifluoromethyl)phenyl)-2-oxazoline reacted with 2- and 1-naphthaldehydes to afford, after hydrolysis, 3-(2-naphthyl)-5-(trifluoromethyl)phthalide (6) and 3-(1-naphthyl)-5-(trifluoromethyl)phthalide (7), respectively.Hydriodic acid reduction of these phthalides yielded 2-(2-naphthylmethyl)-4-(trifluoromethyl)benzoic acid (8) and 2-(1-naphthylmethyl)-4-(trifluoromethyl)benzoic acid (9), which were cyclized and oxidized to 9-(trifluoromethyl)-7,12-benzanthraquinone (10) and 10-(trifluoromethyl)-7,12-benzanthraquinone (11), respectively.Reaction of these quinones with methyllithium followed by stannous chloride-hydrochloric acid reduction of the resulting diols gave 9-(trifluoromethyl)-7,12-dimethylbenzanthracene (12) and 10-(trifluoromethyl)-7,12-dimethylbenzanthracene (13), respectively.In a different route, 2-(3-(trifluoromethyl)benzoyl)-1-naphthoic acid (15), prepared from m-(trifluoromethyl)phenylmagnesium bromide (14) and 1,2-naphthalic anhydride, was reacted with methylmagnesium bromide to obtain 2-<1-hydroxy-1-(3-(trifluoromethyl)phenyl)ethyl>-1-naphthoic acid lactone (16).Zinc-alkali reduction of 16 yielded 2-<1-(3-(trifluoromethyl)phenyl)ethyl>-1-naphthoic acid (17), the acid chloride of wich afforded 1-acetyl-2-<1-(3-(trifluoromethyl)phenyl)ethyl>naphthalene (18) on treatment with lithium dimethylcuprate.Although 2-<(3-(trifluoromethyl)phenyl)hydroxymethyl>-1-naphthoic acid lactone (19), obtained by the reduction of 15 with triethylsilane, underwent a reductive ring closure to 9-(trifluoromethyl)benzanthracene (20), attemped cyclization of 18 did not yield the anticipated 12.