Intermolecular conjugate addition of alkyl radicals on solid phase

The conjugate addition of alkyl radicals, generated photolytically from the corresponding Barton esters, to acrylate immobilized on solid-phase was investigated. Using cross-linked polystyrene, acrylic acid was loaded with either the Wang or Rink linkers, and the reactions were carried out with 10 equiv of Barton ester. The yields following resin cleavage by trifluoroacetic acid were comparable to Barton's solution-phase results. TentaGel resins gave approximately 15% poorer yields, possibly due to radical quenching by the poly(ethylene glycol) spacer. With the Barton ester from cyclopent-2-enylacetic acid, the initial product of conjugate addition is capable of further intramolecular cyclization followed by attack of a second acrylate chain, resulting in polymer cross-linking.