SYNTHESIS OF MEDIUM-SIZED LACTONES BY THE COPPER(I)CHLORIDE/2,2'-BIPYRIDINE-CATALYZED CYCLIZATION OF DICHLOROACETATES AND TRICHLOROACETATES

Medium-sized lactones (eight- to eleven-membered rings) are efficiently formed by Cu(bpy)Cl catalyzed cyclization of various alkenyl di- and trichloroacetates at temperatures between 80 and 190 degrees C in 1,2-dichloroethane or benzene as solvents. The mechanism of the alkene addition reaction is best understood as a chlorine atom transfer process through radical type intermediates. Exclusive endo-cyclization is observed in all cases. Ten and eleven-membered lactones are only accessible by the 'rigid chain' approach, in which an alkene or alkene function is incorporated in the chain connecting the reaction centres, thus reducing the flexibility of the molecule.