Substitution of Secondary Benzylic Phosphates with Diarylmethyl Anions

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 (ArCH2)-C-2 (Ph2CH2,9H-xanthene and fluorene) and n-BuLi at -15 degrees 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. (C) 2019 Elsevier Ltd. All rights reserved.