SKELETAL REARRANGEMENT OF 8-METHYLENEBICYCLO[4.2.0]OCTAN-2-ONES WITH MERCURY(II) PERCHLORATE

Skeletal rearrangement of C6-substituted 8-methylenebicyclo[4.2.0]octan-2-ones 1a-d and 16 with mercury(II) perchlorate was examined, and the remarkable substituent effect on the rearrangement was elucidated. Reactions of the ketones la and Ib having methyl and ethyl groups with Hg(ClO4)(2) . 3H(2)O gave the bicyclo[2.2.2]octanones 2a,b and 3a,b along with a small amount of the bicyclo[3.3.1]nonanones 4a,b, respectively. The yield of the bicyclo[3.3.1] ketone 4c increased in the reaction of the isopropyl derivative Ic. The tert-butyl derivative Id afforded the bicyclo[3.3.1]nonanone 4d as a major product together with a mixture of the bicyclo[2.2.2]octanones 2d and 3d. The remarkable substituent effect is explained based on the stability of the conformers 7 and 10 of the postulated intermediate 6. The intermediacy of 6 was verified by reaction of 6b prepared independently under similar conditions. Similar treatment of the tricyclic ketone 16 yielded the bicyclo[3.3.1]nonanone 19 as a major product along with a small amount of the bicyclo[2.2.2] ketones 17 and 18. The structures of products were determined by NMR spectral data including 2D C-13-INADEQUATE spectrum of 19 and the X-ray crystallographic analysis of 4d. (+/-)-Desdimethyldihydroclovene (22) was easily synthesized from 19 via radical deoxygenation followed by transformation of the tertiary hydroxyl group to the methyl group.