PHOTOCHEMISTRY OF 7,7-DISUBSTITUTED ,4A,5,6,7-HEXAHYDRO-4A-METHYL-1(2H)-NAPHTHALENONES

The photochemistry of (+/-)-3,4,4a,5,6,7-hexahydro-4 alpha-methyl-7,7- diphenyl-1(2H)-naphthalenone (1) and 6,7-hexahydro-4a,7,7-trimethyl-1( 2H)-naphthalenone (2) is presented. Both molecules incorporate a rigid s-cis enone extended over two rings. In benzene, substrates 1 and 2 w ere photoinert. In alcohol solvents, hydrogen bonded enols resulting f rom solvent addition to the enone double bond were isolated as the onl y photoproducts. The rearrangements anticipated for gamma,gamma-disubs tituted enones, aryl migration for 1 and Type A rearrangement for 2, w ere not observed. Spectroscopic and X-ray structure elucidation showed that solvent addition is highly regio-and stereospecific. Ketonizatio n of the less hindered enols derived from 2 was observed upon heating or exposure to silica gel; enols produced from 1 were stable. Photolys is of 1 and 2 in aqueous dioxane led exclusively to beta-hydroxy keton es. The mechanism leading to product formation was rationalized in ter ms of a stepwise addition of solvent to a triplet-derived ground state trans enone. A mechanism involving direct addition of solvent to a po larized excited state was also considered. (C) 1997 Elsevier Science S .A.