COMPOUNDING SELECTIVITY IN REACTIONS OF DIASTEREOISOMERIC RADICAL INTERMEDIATES - AN EXPERIMENTAL DEMONSTRATION THAT THE YIELD OF A PRODUCTFROM A DIASTEREOTOPIC-GROUP-SELECTIVE REACTION CAN SIGNIFICANTLY EXCEED THE LEVEL OF GROUP SELECTIVITY

Reduction of a bis-radical precursor, 6-phenyl-1,1 ropyl]-3a,4-dihydro -1H,3H-cyclopenta[c]furan-5-one (6), with 3 equiv. of Ph(3)SnH provide s mixtures of cis,cis- or cis,trans-angular triquinane products (3a al pha,5a beta,8 beta,8aR)- and (3a alpha,5a alpha,8 ropyl-8-phenyl-5H-d icyclopenta[b,c]furan-7(8H)-one (cis,cis-12/ris,trans-12), in yields t hat vary from 50%/50% to 91%/6% depending on the reaction concentratio n. A mechanistic model for this process is proposed that involves a no n-selective phenylselenium-group abstraction step followed by successi ve kinetic resolutions of diastereoisomeric radical intermediates. Thi s reaction shows how yields in group-selective reactions can be compou nded to levels above that ostensibly permitted by the level of the gro up-selective step.