Photochemical Behavior of Δ4-3-Oxo, Δ5-7-Oxo, and Δ1-3-Oxo Steroids in Concentrated Acid Solution

Article abstract of DOI:10.1021/jo00245a013

Irradiation with UV light of 5α-androst-1-en-3-one (9) in concentrated sulfuric acid leads to 15 and 16; similarly 4a-methyl-4a,5,6,7,8,8a-hexahydronaphthalen-2(1H)-one (10) gives 17 and 18.The formation of the four products is rationalized in terms of a photochemically induced 1,2-alkyl shift to the positively charged positions of the starting carbenium ions.On the other hand, irradiation under the same conditions of 4, 8, 7, and 11 yields, quantitatively, unchanged starting material, while the analogous bicyclic compound Δ^1,9-10-methyl-2-octalone (1) has been reported to yield photorearrangement products.The lack of reactivity of 7 and 11 can be explained according to the proposed mechanism for the photorearrangement of 1.In the case of 4 and 8, the presence of the steroid rings C and D prevents the photorearrangement, but the mechanistic explanation of this effect cannot be determined from the present experimental data.