Cumyl Phenyl Sulfide Forms Bicumyl Instead of Cumyllithium Upon Reductive Lithiation. Thiophenoxide as a Leaving Group in Nucleophilic Substitution by SET.

Abstract Upon reduction with aromatic radical-anions, cumyl phenyl sulfide (1S) yields mainly bicumyl (2) rather than the expected cumyllithium (3), despite a literature report, herein revealed to be in error, that anion 3 is produced. Related examples from the literature are compiled. A suggested mechanism involves a single electron transfer from the generated cumyllithium (3) to the cumyl phenyl sulfide (1S) leading to thiophenoxide anion and two cumyl radicals, which mainly couple in a solvent cage. Such a thiophenoxide displacement by anion 3 has been demonstrated experimentally. Para tert-butyl groups, either on the phenyl or cumyl ring, increase the ratio of the cumyllithium to the bicumyl, presumably by sterically inhibiting the pi complexation thought to be necessary for electron transfer.