A NEW ENANTIOSELECTIVE APPROACH TO THE BICYCLO[4.4.0]DECANE AND BICYCLO[4.3.0]NONANE SYSTEMS

Highly diasteroselective routes to cis-fused bicyclo[4.4.0]decane-2,10-diones and bicyclo[4.3.0]nonane-2,9-diones from 5-trimethylsilyl-2-cyclohexen-1 -one (1a) and its 3-methyl derivative were established by utilizing an annulation with Ω-(alkoxycarbonyl)alkylzinc reagents. Bicyclo[4.4.0]decane-2,8-dione was obtained diastereoselectively by the double Michael reaction of 1a with dienol silyl ether. The diastereoselective Diels-Alder reaction of 1a with cyclopentadiene gave an endo adduct, which can be regarded as a new chiral cyclohexenone synthon, with a high optical purity.