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Substitution of Secondary Benzylic Phosphates with Diarylmethyl Anions

Author:
Shinohara, Riku, Kawashima, Hidehisa, Ogawa, Narihito, Kobayashi, Yuichi
Source:
Tetrahedron 2019 v.75 no.18 pp. 2717-2725
ISSN:
0040-4020
Subject:
anions, biphenyl, chemical reactions, chemical structure, fluorenes, phosphates, stereochemistry
Abstract:
Substitution of diethyl and diphenyl benzylic phosphates, Alk-CH(Ar1)OP(O)(OR)2 (R = Et, Ph; Alk = Me, Et, i-Pr; Ar1 = aryl), with the anions derived from Ar2CH2 (Ph2CH2,9H-xanthene and fluorene) and n-BuLi at –15 °C was studied. For phosphates with Me as an Alk, diethyl phosphates produced Me-CH(Ar1)CH(Ar2)2 (Ar1 = 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.
Agid:
6357934