HIGH 1,2-ASYMMETRIC INDUCTION IN RADICAL REACTIONS - RADICAL-ADDITIONTO GAMMA-HYDROXY ALPHA,BETA-UNSATURATED CARBOXYLIC ESTERS AND SULFONES

High 1,2-asymmetric induction was realized by the addition of a 1-hydr oxy-1-methylethyl radical to conformationally flexible (E)-gamma-hydro xy alpha,beta-unsaturated carboxylic esters and sulfones (1 and 2, res pectively). Upon the irradiation (>290 nm) of (E)-1 and benzophenone i n 2-propanol, the 1-hydroxy-1-methylethyl radical was generated in sit u and added to (E)-1 with high anti-stereoselectivity. The bulkier is the gamma-alkyl group of (E)-1, the higher does the selectivity become . Similarly, a radical addition to the acetates of (E)-1 and (E)-2 pro ceeded stereoselectively in an anti fashion, whereas (Z)-2 exhibited s yn-stereoselectivity. The mechanism for these stereoselective radical additions is discussed.