The mechanism of phosphonium ylide alcoholysis and hydrolysis: concerted addition of the O-H bond across the P=C bond

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Byrne, Peter A.
Gilheany, Declan G.
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The previous work on the hydrolysis and alcoholysis reactions of phosphonium ylides is summarized and reviewed in the context of their currently accepted mechanisms. Several experimental facts relating to ylide hydrolysis and to salt and ylide alcoholysis are shown to conflict with those mechanisms. In particular, we demonstrate that the pK(a) values of water and alcohols are too high in organic media to bring about protonation of ylide. Therefore, we propose concerted addition of the water or alcohol O-H bond across the ylide P=C bond. In support of this, we provide NMR spectroscopic evidence for equilibrium between ylide and aclohol that does not require the involvement of phosphonium hydroxide. We report the first P-alkoxyphosphorane to be characterised by NMR spectroscopy that does not undergo exchange on an NMR timescale. Two-dimensional NMR spectroscopic techniques have been applied to the characterisation to P-alkoxyphosphoranes for the first time.
Catalytic Wittig reaction , Nuclear-magnetic-resonance , Nuclear magnetic resonance , Tertiary phosphine oxides , Alkaline hydrolysis , Thermal decomposition , Equilibrium acidities , Heteroarylphosphorus compounds , Nucleophilic displacement , Alkoxyphosphonium halides , Substitution reactions , Alkoxyphosphorane , Concerted additions , Hypervalent compounds , Reaction intermediates , Ylides
Byrne, P. A. and Gilheany, D. G. (2016) 'The Mechanism of Phosphonium Ylide Alcoholysis and Hydrolysis: Concerted Addition of the O−H Bond Across the P=C Bond', Chemistry – A European Journal, 22(27), pp. 9140-9154. doi: 10.1002/chem.201600530
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. This is the peer reviewed version of the following article: P. A. Byrne, D. G. Gilheany, Chem. Eur. J. 2016, 22, 9140., which has been published in final form at This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.