Addition of lower or higher order cuprates to the enone homoketals 4a-d give the alkylated products with de's ranging from 12% to 34%.
The efftcient production of optically active materials from prochiral precursors by asymmetric induction is one of the goals in synthetic organic chemistry today.1 Of the several diverse methods for accomplishing this aim, one that has received significant attention recently is the use of homochiral ketals cr acetals in diastereoselective processes. Notable in this regard is the work of hfash,z who has published extensively on the cyclopropanation (via Simmons-Smith reaction) of homochiral ketals of enones using chirall,2dio1s, and that of Oku,s who has reported selective formation and reactions of diasmmomeri c spiroketals from meso 1,2-and 1,3diols and 1-menthone. We have been interested in the potential diastereoselective addition of nucleophiles to homochiral kctals of more highly functional&d enones, especially those with electron-withdrawing groups in the S-position. We now report our results on the addition of organocuprates to 1-acetylcycl~tenes bearing various homochiral ketals at the 3position.
We hoped that addition of an organocuprate (Scheme 1) to the ketal C (pmpamd from the readily available precursors cyclohexenone A and various optically active 1,2diols B) would proceed with high diastereoselectivity from the less hindemd top face of the ketal in order to avoid intaaction with the alkyl group on the ketal on the bottom face (as shown in D). The resultant stabilized lithium anion E could tbcn bc kapped with various electrophiles tram to the alkyl group to give predominately F. Hydrolysis would then affotd the optically active ketone G and regenerate the optically active did B. Alternatively protonaton of E followed by basecatalyzed cpimerixation should give the tram 1,2disubstituted cyclopentane H and after hydrolysis I. Compounds such as G or I might be of value in the synthesis of cyclopentenone natural products such as prostaglandin A and didemnenone