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 Ph3SnH provides mixtures of cis,cis‐ or cis,trans‐angular triquinane products (3aα,5aβ,8β,8aR*)‐ and (3aα,5aα,8β,8aR*)‐hexahydro‐3a‐propyl‐8‐phenyl‐5H‐dicyclopenta[b,c]furan‐7(8H)‐one (cis,cis‐12/cis,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.