Journal of the Chemical Society. Perkin transactions I p. 1454 - 1459 (1981)
Update date:2022-08-04
Topics:
Waring, Anthony J.
Zaidi, Javid Hussain
Pilkington, James W.
Two mechanisms are well established for the dienone-phenol rearrangements of bicyclic cyclohexadienones of the 4a-alkyl-5,6,7,8-tetrahydronaphthalen-2(4aH)-one type, of which the 4a-methyl compound (1) and the steroidal 1,4-dien-3-ones are examples.They involve, for (1), either a direct alkyl shift from C-4a to C-4 and deprotonation to give a 4-alkyl-5,6,7,8-tetrahydro-2-naphthol or a shift of the 4a,5-bond from C-4a to C-8a with formation of a spiran intermediate and further ring migration from C-8a to C-1 to form a 4-alkyl-5,6,7,8-tetrahydro-1-naphthol.A further mechanism, for which there was little strong evidence, involves an alkyl shift from one angular position, C-4a, to the other, C-8a, followed by further ring migrations via a spiran intermediate to give an additional route to the 4-alkyltetrahydro-2-naphthol product.The products of rearrangement of 3,4a- and 1,4a-dimethyl-5,6,7,8-tetrahydronaphthalen-2(4aH)-ones in aqueous sulphuric acid, and in acetic anhydride with sulphuric acid catalysis, have been studied critically.The use of quantitative 13C n.m.r. spectroscopy confirms the identity and ratios of products deduced using 1H n.m.r. spectroscopy and other techniques.The results show that the third, suspect, mechanism does indeed operate, and that it contributes significantly to the formation of 4-alkyltetrahydro-2-naphthol products from both dienones.
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