SYNTHESIS AND PHOTOCHEMICAL-REARRANGEMENT OF (1R,7AS)-1-(TERT-BUTYLDIPHENYLSILOXY)-7A-METHYL-5(7AH)-INDANONE

Reaction of (1S,7aS)-1-hydroxy-7a-methyl-7,7a-dihydro-5(6H)-indanone (5a) with benzoic acid under the usual conditions of the Mitsunobu reaction gave a low yield of a 1:1 mixture of the benzoate derivatives 6b and 5b resulting from inversion and retention of configuration, respectively, at C-1. Under conditions in which the benzoic acid concentration was kept low, only the inversion product 6b was obtained but the extent of conversion of the alcohol to the ester was low. The substitution of p-nitrobenzoic acid for benzoic led to a significant improvement in the yield of the inversion product 6c. Several other methods of obtaining alpha-oxy derivatives of the type 6b-e were explored but with little or no success. The reaction of the tosyloxy enone 5d with azide ion and cyanide anion gave enones of the type 12 resulting from retention of configuration at C-1 largely or exclusively. The (p-nitrobenzoyl)oxy derivative 6c was converted into the corresponding cross-conjugated cyclohexadienone, (1R,7aS)-l-(tert-butyldiphenylsiloxy)-7a-methyl-5(7aH)-indanone (4a), which was irradiated in glacial and in aqueous acetic acid. In the former solvent, the dienone system underwent photochemical rearrangement to give the 5/6-fused acetoxyl enone 14 and a 2:1 mixture of the tricyclic cyclopropyl ketone 15 and 16 in 25% and 17% yields, respectively, but in aqueous acetic acid phenolic products 18 and 20, obtained by thermal cleavage of the 1,7a carbon-carbon bond, were obtained almost exclusively. In contrast, under the same photolysis conditions, the dienone 1a, the C-1beta epimer of 4a, gave a mixture of photoproducts composed of the 5/6-fused hydroxy ketone 21, the 5/6-fused acetoxy ketone 2a, and the tricyclic conjugated cyclopropyl ketone 22 in 47%, 5%, and 15% yields, respectively.