CARBOCYCLIC CONSTRUCTION BY THE [2,3]SIGMATROPIC REARRANGEMENT OF CYCLIC SULFONIUM YLIDES - A NEW ENTRY FOR THE STEREOSELECTIVE SYNTHESIS OF SUBSTITUTED CYCLOHEXANONES

The rhodium(II)-catalyzed cyclization of acyclic alpha-diazo-beta-keto esters 1c,d provided stereoselectively the highly substituted cyclohexanones 3c,d respectively, by the [2,3]sigmatropic rearrangement via stereocontrolled nine-membered allysulfonium ylides 2c,d. Further elaboration of 3d toward the cyclohexanone 36 accomplished asymmetric formal syntheses of the representative elemanoids, 37 and 38. The compound 3c was transformed into the cyclohexanone 34a and cyclohexene 43, which could serve as the key intermediates for the synthesis of natural products possessing contigously cis-arranged trimethylcyclohexanone and its related moieties, respectively.