NOVEL PHOTOCHEMICAL-REACTIONS OF 1-NAPHTHOL AND 2-NAPHTHOL WITH ETHYLENE PROMOTED BY ALUMINUM HALIDES

Novel photoreactions of 1- and 2-naphthols with ethylene promoted by a luminum halides are described. Irradiation of 2-naphthol (2a) with AlX 3 (X = Cl, Br) and ethylene in CH2Cl2 gave the corresponding [2 + 2] c ycloadduct 7a in good yields. The major side product was 2-ethyl-1-nap hthol (8a). Of the Lewis acids and alkenes examined, only AlCl3 and Al Br3 effected the reaction and only ethylene gave satisfactory results, although allene can also be employed. Naphthols 2b-e having different electron-attracting substituents on C-6 afforded [2 + 2] adducts 7b-e in moderate to good yields, while the reactions of C-3-alkyl-substitu ted derivatives 8a and 15b were unsuccessful. By contrast, 1-naphthol (1a) and its derivatives 1b-e exhibited diverse reactivities depending on the substituent on C-2, C-3, or C-6. Namely 1a and 3-methyl deriva tive 1b afforded [2 + 2] cycloadducts 16a and 16b in moderate yields. On the other hand, 2-methyl and 2-propyl derivatives 1c and 1d yielded unusual products like indenones 22a and 22b and cyclopropyl ketones 2 3a and 23b, respectively. 6-Methoxy derivative 1e also gave indenone 3 0. Plausible reaction mechanisms leading to the observed products are presented.