STUDY OF REACTIONS LEADING TO SULFINE FORMATION .6. BASE-CATALYZED DECOMPOSITION OF DI-9-FLUORENYL SULFOXIDE

When treated with CH3ONa in CH3OH-CH2Cl2, di-9-fluorenyl sulfoxide (3) undergoes elimination readily to afford 9-thiofluorenone S-oxide (4) and fluorene (eq 2). Comparison of the rate of the elimination to the rate of disappearance in the presence of CD3OD of the H-1 NMR signal for the 9-H in 3 shows that the mechanism of this sulfine-forming elimination is (E1cB)rev, the rate of cleavage of the intermediate alpha-sulfinyl carbanion 7 to give 4 and a 9-fluorenyl carbanion being over 100 times slower than the rate at which 7 is protonated to regenerate 3. The (E1cB)rev behavior of this elimination is contrasted with the (E1cB)rev/(E1cB)irrev borderline behavior of the elimination of diarylmethyl (arylmethyl)sulfonyl sulfoxides 1, 2 and a reason for this at first sight unexpected difference in behavior is presented.