Diastereoselective synthesis of 4-substituted L-prolines by intramolecular radical cyclization of N-aryl sulphonyl-N-allyl 3-bromoalanines: Interesting dependence of selectivity on the nature of sulphonamido groups

Enantiopure 4-substituted L-proline derivatives have been prepared via intramolecular radical cyclization of N-aryl sulphonyl-N-allyl-3-bromo-L-alanines in high yields. Surprisingly, the extent of selectivity was found to be primarily dependent on the nature of sulphonamido aryl group and could be as high as 33:1 using naphthyl sulphonamide.