Wittig reaction theoretical studies

Volatron, F., Eisenstein, O. Wittig versus Corey-Chaykovsky Reaction. Theoretical study of the reactivity of phosphonium methylide and sulfonium methylide with formaldehyde. J. Am. Chem. Soc. 1987, 109, 1-4. 

The notable increases in theoretical studies of ylides and their reactions reflects similar developments throughout organic chemistry. The renewed interest in the mechanism of the Wittig reaction have continued, but in spite of several years of considerable effort from a number of respected research groups a fully satisfactory explanation is still some way off. 

The thio-Wittig reaction, like the Wittig itself, may involve (thia)phosphetane or betaine-type structures as intermediates. A combined experimental and theoretical study over a wide range of conditions and of substrates (aliphatic vs aromatic, aldehyde- vs ketone-derived) suggests a mechanistic continuity, with solvent polarity and substrate electronic effects being the main influences on the transition from one mechanism to another. ... 

M. Seth, H. M. Senn and T. Ziegler, The influence of solvation and finite temperatures on the Wittig reaction A theoretical study, J. Phys. Chem. A, 109 (2005) 5136-5143. 

Mechanistic and Theoretical Studies of Phosphonium Ylides and the Wittig Reaction. - The physico-chemical nature of the P-C bond in phosphonium ylides is complex and, despite intensive research over many years, remains the subject of dispute Numerous theoretical studies of this problem have appeared in the scientific literature. A recent contribution to this area by Mitrasinovic uses sharing indices and sharing amplitudes to study P-C bonds in a number of tri-and penta-valent phosphorus species. Sharing indices and amplitudes are quantitative, orbital dependent, measurements of the degree to which an electron, as a wave, is shared between two spatial points in a many electron system. Ylides studied using this method include (1), (2) and (3). ... 

PhCH2NPPh3 affords the isocyanide derivative [Os3(CO)g(CNCH2Ph)(n3-ri rri iTi -Ceo)]. The Staudinger reaction in combination with an intramolecular aza-Wittig ring closure reaction has been applied in the synthesis of quinazolin-4-ones. Other examples of intramolecular aza-Wittig reactions are reported as parts in multi-step synthetic routes. A theoretical study of the aza-Wittig reaction of HN = PX3(X = H and Cl) with formaldehyde in the gas phase and in solution has been reported. ... 

Restrepo-Cossio, A. A., Cano, H., Mari, F., Gonzalez, C. A. Molecular modeling of the Wittig reaction. 6. Theoretical study of the mechanism of the Wittig reaction ab initio and MNDO-PM3 treatment of the reaction of unstabilized, semistabilized and stabilized ylides with acetaldehyde. Heteroatom Chem. 1997, 8, 557-569. 

Theoretical, Structural and Mechanistic Studies of Phosphorus Ylides and the Wittig Reaction. - In contrast to previous years there are no significant new theoretical or mechanistic studies to report. However, investigations into the structural nature of ylides continue to provide much of interest. 

The reaction of an azide RN3 and a phosphine PR 3 yields the reactive phos-phoranimine (iminophosphorane) RN=PR 3 under elimination of a nitrogen molecule. Phosphoranimines play an important role in synthetic organic chemistry and are useful precursors for a subsequent aza-Wittig approach, leading to various nitrogen-containing compounds. A theoretical study shows the polarity, and consequently, the reactivity of the N=P bond to be dependent on the nature of the phosphorus substituents. ... 

The number of publications reporting theoretical studies and those reporting mechanistic studies have increased following the reduction in these numbers last year. One of these reports includes the isolation and separate decomposition of certain oxaphosphetanes and this has allowed the first kinetic study of the second step of the Wittig reaction, albeit for a rather special system. Complex phosphonate carbanions and ylides continue to be widely used in synthesis and the number of reports of the use of the aza-Wittig and related reactions in heterocyclic synthesis remain at last year s high level. 

Amongst theoretical calculations for these systems is included a quantum chemical study of the 7c-eIectron delocalization in triphenylphosphonium ylides, leading to an evaluation of the criteria for reactivity and aromaticity in the Wittig reaction. It was predicted that the as yet unknown ylide (1 X = PPhg) will not take part in the Wittig reaction. ... 

A joint experimental and theoretical study has indicated that the gas-phase [1,2]-Wittig rearrangement is an anionic rather than a radical reaction. The mechanism of... 

Other theoretical insights into the second step of the Wittig reaction have also been reported. These studies included isomerization and thermal decomposition of isolable spiro-l,2-oxaphosphetanes (OPAs). Key features of these investigations were (1) the synthesis of enantio-pure derivatives, (2) the identification of three mechanisms of OPA... 

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