Substitution of Secondary Benzylic Phosphates with Diarylmethyl Anions

Abstract Substitution of diethyl and diphenyl benzylic phosphates, Alk-CH(Ar 1 )OP(O)(OR) 2 (R = Et, Ph; Alk = Me, Et, i -Pr; Ar 1  = aryl), with the anions derived from Ar 2 CH 2 (Ph 2 CH 2 ,9 H -xanthene and fluorene) and n -BuLi at –15 °C was studied. For phosphates with Me as an Alk, diethyl phosphates produced Me-CH(Ar 1 )CH(Ar 2 ) 2 (Ar 1  = 4-halo-, 4-CN, 4-Me-, 2-Me, 2-Br-, 3-MeO-phenyl and 2-naphthyl). However, an unwanted substitution at the Et group competed with phosphates of Alk = Et- and i -Pr. Fortunately, the corresponding diphenyl phosphates cleanly underwent the desired substitution. Two enantioenriched phosphates, MeCH(Ph)OP(O)(OEt) 2 and EtCH(Ph)OP(O)(OPh) 2 , proceeded with complete inversion of the stereochemistry.