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Frontispiece: The Mechanism of Phosphonium Ylide Alcoholysis and Hydrolysis: Concerted Addition of the O−H Bond Across the P=C Bond
Author(s) -
Byrne Peter A.,
Gilheany Declan G.
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Reports
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201682762
Subject(s) - phosphonium , ylide , phosphorane , chemistry , alkoxide , medicinal chemistry , alkyl , solvent , hydrolysis , hydroxide , photochemistry , organic chemistry , catalysis
Ylide Hydrolysis & Alcoholysis The reactions of phosphonium ylides (Ar 3 P=CHR′) with alcohols (ROH) and H 2 O in protic solvents to give alkoxyphosphorane or hydroxyphosphorane, respectively, generally occur through a two‐step pathway involving a phosphonium hydroxide or alkoxide intermediate. In protic solvents, the p K aH of the ylide is typically higher than the p K a of H 2 O or alcohol. In aprotic media, the p K a values of H 2 O and alcohols are dramatically higher than in protic media, and yet formation of phosphorane intermediates is still observed. The characteristic high field 31 P NMR signal of an alkoxyphosphorane formed in an aprotic solvent is shown in the image. On the basis of this observation, and other substantial evidence in support of their interpretation from 1D and 2D NMR studies, P. A. Byrne and D. G. Gilheany conclude in their Full Paper on page 9140 ff. that concerted formation of phosphorane intermediates from ylide+ROH (R=H or alkyl) occurs in any solvent in which the p K aH of the ylide is lower than the p K a of ROH.