Unexpected differences in the α-halogenation and related reactivity of sulfones with perhaloalkanes in KOH-t-BuOH

Most alkyl phenyl sulfones are readily α-chlorinated with CCl4 and α-brominated with CBrCl3 in KOH−t-BuOH via radical−anion radical pair (RARP) reactions. While isopropyl mesityl sulfone (4) is easily α-chlorinated with CCl4, it was completely recovered when treated with the more reactive CBrCl3. Subsequent investigations showed the latter result to be due to the poor acidity of 4 together with the rapid depletion of CBrCl3 and KOH by their reaction with each other, and led to a variety of other important results. 4-Hydroxyphenyl isopropyl sulfone (6) is unreactive with either CCl4 or CBrCl3 in KOH−t-BuOH, its phenoxide anion strongly reducing the electronegativity of the sulfonyl group, thereby inhibiting α-anion formation. This effect is reversed by the electron-withdrawing influence of two α-phenyls, so that benzhydryl 4-hydroxyphenyl sulfone (8) is readily α-halogenated in KOH−t-BuOH with CCl4 or CBrCl3. On further contact with KOH−t-BuOH the α-halogenated sulfones from 8 are decomposed into benzophen...