Rose Bengal-sensitized photo-oxygenations of several bisphenylhydrazones of 1,2-diketones have been studied. The photo-oxygenation of benzil bisphenylhydrazone (9a) gave a mixture of products consisting of 2,4,5-triphenyl-1,2,3-triazole (10a, 27%), benzil (11a, 16%) benzoic acid (12, 33%) and biphenyl (13, 6%), whereas, biacetyl bisphenylhydrazone (9b), under analogous conditions gave a 2% yield of 4,5-dimethyl-2-phenyl-1,2,3-triazole (10b), a 30% yield of biacetyl monophenylhydrazone (16b) and a 1% yield of biphenyl. Cyclohexane-1,2-dione bisphenylhydrazone (9c) gave likewise, the corresponding triazole,10c (19%), cyclohexane-1,2-dione monophenylhydrazone (16c, 18%) and a small amount of biphenyl (13, 2%). Photo-oxygenation of acenaphthenequinone bisphenylhydrazone (9d) gave a mixture of products consisting of acenaphthenequinone monophenylhydrazone (16d, 67%), 1,8-naphthoic anhydride (23, 22%) and biphenyl (13, 9%). The photo-oxygenations of both benzil monophenylhydrazone (16a) and acenaphthenequinone monophenylhydrazone (16d) gave rise to products, similar to those obtained from9a and9d, respectively.
Photo-oxygenation of 1,2-bisphenylazostilbene (18a) gave a 65% yield of the triazole10a, whereas, 2,3-bisphenylazo-2-butene (18b) gave a 16% yield of the triazole10b and a 5% yield of biphenyl. On the other hand, the photo-oxygenation of 1,2-bisphenylazocyclohexene (18c) gave a 77% yield of cyclohexane-1,2-dione (11c). The photo-oxygenation of 1,2-bisphenylazoacenaphthylene (18d) gave a 46% yield of acenaphthenequinone monophenylhydrazone (16d), a 51% yield of 1,8-naphthoic anhydride (23) and a 9% yield of biphenyl.
The photo-oxygenations of both benzil bishydrazone (25) and benzil monohydrazone (27) have been studied. In the case of the former, a mixture of products consisting of a 28% yield of benzil (11a) and a 17% yield of benzoic acid have been isolated, whereas in the case of the latter, a 55% yield of benzoic acid was isolated as the sole product.
Reasonable mechanisms have been suggested for the formation of the various products in the photo-oxygenations of the different substrates that we have examined.