Compounding selectivity in reactions of diastereoisomeric radical intermediates - An experimental demonstration that the yield of a product from a diastereotopic-group-selective reaction can significantly exceed the level of group selectivity

Reduction of a bis-radical precursor, 6-phenyl-1,1 -bis[3-(phenylselanyl)propyl]-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one (6), with 3 equiv. of Ph(3)SnH provides mixtures of cis,cis- or cis,trans-angular triquinane products (3a alpha,5a beta,8 beta,8aR*)- and (3a alpha,5a alpha,8 beta,8aR*)-hexahydro-3a-propyl-8-phenyl-5H-dicyclopenta[b,c]furan-7(8H)-one (cis,cis-12/ris,trans-12), in yields that vary from 50%/50% to 91%/6% depending on the reaction concentration. A mechanistic model for this process is proposed that involves a non-selective phenylselenium-group abstraction step followed by successive kinetic resolutions of diastereoisomeric radical intermediates. This reaction shows how yields in group-selective reactions can be compounded to levels above that ostensibly permitted by the level of the group-selective step.