Groups R1 which are not inert to attack by peroxide in the sense intended herein include aryl esters (???COOAr), alkyl esters (???COOR) wherein the alkyl group R is substituted with electron-withdrawing groups such as halogen, cyano and nitro since these substituents increase the leaving group ability of the ???OR group, alkyl and aryl thioesters (???COSR, COSAr), sulfonimides (???CO(NR)SO2R???),