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Lithium Borohydride for Achiral and Stereospecific Reductive Boronation at Phosphorus: Lack of Electronic Effects on Stereoselective Formation of Alkoxyphosphonium Salts
Author(s) -
Al Sulaimi Sulaiman S.,
Rajendran Kamalraj V.,
Gilheany Declan G.
Publication year - 2015
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201500521
Subject(s) - chemistry , stereoselectivity , diastereomer , stereospecificity , reagent , borane , kinetic resolution , lithium (medication) , enantiomer , sodium borohydride , yield (engineering) , borohydride , aryl , enantiomeric excess , medicinal chemistry , enantioselective synthesis , stereochemistry , organic chemistry , catalysis , materials science , alkyl , endocrinology , metallurgy , medicine
We report LiBH 4 as a preferred, simple and effective reagent for reductive boronation of achiral and racemic chlorophosphonium salts (CPS) and for diastereomeric alkoxyphosphonium salts (DAPS), both of which are, in turn, easily generated from either the corresponding phosphane or, more conveniently, the phosphane oxide. Further, we have shown that the DAPS reduction/boronation could be achieved with complete stereocontrol to give scalemic phosphane–borane directly in excellent yield and enantiomeric excess ( ee ). This new methodology was employed to investigate the effects of aryl substitution on the outcome of dynamic kinetic resolution of arylmethylphenylphosphanes and phosphane oxides via DAPS. It was found that substitution at the ortho position strongly affects the degree of stereoselection. However, surprisingly, we confirmed that there was no variation of stereoselectivity seen with the electronic effect of substituents on the para position.