Novel Photochemical Reactions of 1- and 2-Naphthols with Ethylene Promoted by Aluminum Halides

Article abstract of DOI:10.1021/jo00062a024

Novel photoreactions of 1- and 2-naphthols with ethylene promoted by aluminum halides are described.Irradiation of 2-naphthol (2a) with AlX3 (X=Cl, Br) and ethylene in CH2Cl2 gave the corresponding <2+2>cycloadduct 7a in good yields.The major side product was 2-ethyl-1-naphthol (8a).Of the Lewis acids and alkenes examined, only AlCl3 and AlBr3 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-substituted 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 derivative 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 23a and 23b, respectively. 6-Methoxy derivative 1e also gave indenone 30.Plausible reaction mechanisms leading to the observed products are presented.