SELECTIVE ORTHO LITHIATION OF (2,5-DIMETHOXYPHENYL)DIPHENYLPHOSPHINE OXIDE AND TRAPPING OF THE RESULTING ARYLLITHIUM WITH ELECTROPHILES

The title compound undergoes predominant 6-lithiation, ortho to the methoxy and phosphinoyl groups, on reaction with t-BuLi in THF under conditions of thermodynamic control at low temperature. The organolithium compound is stable at least to 0-degree-C and can be trapped by a range of electrophiles to give the corresponding tetrasubstituted (diphenylphosphinoyl)arenes in moderate to good yield. The iodide formed by this sequence undergoes Ullman coupling to the diphenyl, which exhibits a novel restricted rotation phenomenon, in good yield under mild conditions. (2,5-Dimethoxyphenyl)diphenylphosphine sulfide lithiates exclusively at the 4-position under the same conditions, whilst the corresponding phosphine is unreactive.