The Mechanism of Phosphonium Ylide Alcoholysis and Hydrolysis: Concerted Addition of the O−H Bond Across the P=C Bond

Abstract

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 pKa 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.

Reduction of Activated Alkenes by PIII/PV Redox Cycling Catalysis

“…Subsequently, the ylide intermediate is formed by a protonation/deprotonation sequence. Hydrolysis of the ylide liberates the product, and the phosphane oxide is regenerated …”

P−B Desulfurization: An Enabling Method for Protein Chemical Synthesis and Site‐Specific Deuteration

“…In the next step, the carbon atom of the C−S bond is attacked by another molecule of phosphine to give phosphonium salt F and phosphine sulfide. Salt F undergoes alkaline hydrolysis to produce the desulfurized product H via intermediate G , in which a proton from water (or deuterium from D 2 O) is transferred to the carbon center. As evidence for this mechanism, both the phosphine oxide and the phosphine sulfide derived from TCEP were observed in the desulfurization process.…”

Synthesis, Properties and Stereochemistry of 2-Halo-1,2λ5-oxaphosphetanes

“…One of the most interesting and intriguing classes of organophosphorus compounds are the 1,2-oxaphosphetanes—four-membered heterocycles containing pentacoordinated phosphorus [1,2,3,4,5,6,7]. Since 1,2-oxaphosphetanes are well-known intermediates in the Wittig reaction, a number of efforts have been made for their structural characterization both in solution and the solid state [8,9,10,11,12,13].…”

“…Gilheany studied oxaphosphetane intermediates in the Wittig reaction by variable-temperature NMR spectroscopy [9,10,11]. Compound 13 was obtained by low-temperature acid quenching of the Wittig reaction of ylide with benzaldehyde, a suitable representative aromatic aldehyde (see Scheme 6).…”

“…Among the stable oxaphosphetanes [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22], 2-halo-1,2λ 5 -oxaphosphetanes 14 , which possess relatively high stability and diverse reactivity, attract particular interest [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38] (Scheme 7). These oxaphosphetanes containing fluorine, chlorine or bromine atoms bonded to phosphorus are an interesting class of pentacoordinated phosphorus heterocycles possessing peculiar properties.…”