Development of solid-phase radical reactions using oxime ethers as a radical acceptor

Triethylborane has the potential to induce radical reactions on solid support and the solid-phase radical reactions were achieved by using triethylborane as a radical initiator. The intermolecular carbon radical addition to glyoxylic oxime ether anchored to Wang resin proceeded under very mild conditions to give cr-amino acid derivatives in good yield without interference of the polystyrene skeleton of the resin. Diethylzinc also worked well as a radical initiator at low reaction temperature. Thus, the employment of triethylborane or diethylzinc at low reaction temperature facilitated the control of stereochemistry in solid-phase reactions. Alkyl radical addition to Oppolzer's camphorsultam derivatives of oxime ether anchored to a polymer support proceeded smoothly even at -78 degrees C to give the alpha-amino acid derivatives with excellent diastereoselectivities. The radical cyclization of oxime the ethers anchored to a polymer support also proceeded effectively to provide functionalized pyrrolidines via a carbon-carbon bond-forming process.