Phospha-Wittig reaction

Two hindered phosphoranylidenephosphines, ArP=PMc3 [76 Ar = 2,6-dimesityl-phenyl and 2,4,6-tri(r-butyl)phenyl], have been prepared and are stable in the absence of air and water. As the resonance suggests, they can enter into phospha-Wittig reactions to produce phosphaalkenes (77). The reaction gave high yields of ( )-(77) in a few hours for a range of benzaldehydes (p-Cl/N02/0Me/NMe2/H, F5), and also for ferrocenecarboxaldehyde and pivaldehyde, but was unsuccessful for ketones. 

The existence of oxaarsetanes during an arsa-Wittig reaction has been proved by H and 170 NMR spectroscopy.40 75As NMR spectra were obtained from the corresponding arsonium salts and arsane oxides. It has been shown that the reaction mechanism of the arsa-Wittig reaction is identical with that of the phospha-Wittig reaction. 

The phospha-Wittig reaction between [W(CO)5] adducts of phosphinidene phosphoranes or phosphoranyl phosphides and organocarbonyl compounds provides an elegant complementary route to reactive phosphaalkene complexes.20-23 Accordingly, 28 converts an a,/3 unsaturated aldehyde into a transient 1-phosphabutadiene complex 29, which instantaneously cyclizes to 30, as shown in Eq. (10).23... 

Compound 74, which results from a phospha-Wittig reaction via the 1-phospha-1,3-butadiene complex 73, according to Scheme 19, is even more reactive toward alkynes than 26 or 25, respectively. The complex smoothly reacts with alkynes to afford the 1,4-dihydrophosphinine complexes 75a-d. In the case of unsymmetrical alkynes, the cycloaddition is regioselec-tive and seems to be controlled by steric rather than by electronic factors. Less electron-rich 1,2-dihydrophosphete complexes with alkyl or phenyl substituents in the 3- and 4-positions are not sufficiently reactive toward alkynes.44... 

Particularly notable modifications of the fundamental Wittig reaction are those described as a phospha-Wittig process (as illnstrated in equation 18) and the aza-Wittig process (as illnstrated in equation 19) and useful for the preparation of secondary amines. ... 

The bis(methylenephosphonium ylide) platinum complex (61) reacts with 3-butyn-l-ol to give the vinylphosphonium salt (62) and evidence is presented for intermediate formation of the carbene complex (63). Phosphoranylidenephosphine complexes (64) have been synthesized and shown to undergo "phospha-Wittig" reactions with aldehydes to give the phosphaalkene complexes (65) which can be isolated or trapped. ... 

Ylides Coordinated to Metals.- The "phospha-Wittig" reaction has been reported for the first time. The phosphonate-stabilised phosphide (65) (prepared by base treatment of the tungsten complex (64)) reacts with carbonyl compounds to give phosphaallene complexes (66). 

There has so far been only limited success in attempts to produce P-C compounds directly from elemental phosphorus, although both white and red forms are subject to attack by a variety of nucleophilic reagents. These and other synthetic methods are discussed below in this chapter. Synthesis of P-C bonds has recently been comprehensively reviewed [21]. The synthesis of P=C and P=C bonds is dealt with in Sections 6.14 and 6.15 (see also Phospha-Wittig reaction (6.445)). Carbophosphenes can be obtained from carbophosphynes and vice versa (6.631,6.631a), although these are not general methods of preparation. 

The highly significant stereochemical implications of the Wittig reaction are discussed in Chapter 3.3. Aza-Wittig and Phospha-Wittig reactions are known (6.457, 6.458). Betaine-like structures (3.112) are found in some quasi-phosphonium derivatives. 

The alkylation of anions derived from 78 with styrene oxide afforded the diastereomeric mixture of 79 through a phospha-Wittig reaction with very little asymmetric induction from the menthyl group. In these reactions, complete inversion of configuration of the stereogenic oxirane carbon was observed. The individual diastereomers of 79 could be separated by column chromatography or recrystallisation. Decomplexation with dppe furnished the free enantiopure phosphiranes, which were complexed to Rh. ... 

Nb and Ta derivatives are hard acids and then-complexes with P- or As-donors are limited. Tertiary phosphines, especially PMes, have been widely used to stabilize low-valent derivatives. C-H activation reactions, promoted by the formation of thermodynamically stable Ta-H, Ta-C, and Ta=C bonds have resulted in metallacycles based on unusual anionic phosphorus donors. Nucleophilic Ta phosphinidene complexes could be stabilized by a tripodal tetradentate [NN3] amido ligand. The terminal PR ligand reacts smoothly with aldehydes, providing a general synthesis of phosphaalkenes RP=C(H)R and act thus as a phospha-Wittig reactant see Phosphorus Organophosphorus Chemistry). 

Terminal phosphinidene-metal complexes, L TM=PR, readily add to double bonds (equation 17). Both metal-stabilized and phosphine-stabilized phosphinidenes, R P= PR3, can act as phospha-Wittig reagents, which undergo metathesis reactions with carbonyl-containing compounds to generate carbon phosphorus double bonds (equations 18 and 19). Pnictinidenes and their complexes have been extensively reviewed in terms of both their syntheses and reactivities. ... 

Finally, Shah and Protasiewicz have reviewed what they term phospha-variations of the Wittig and aza-Wittig olefination reactions where a phospha-Wittig is one that uses phospha-ylides , such as phosphoranylidene-o -phos-... 

Consequently, phospha-l,2-dioxetanes are the only reasonable intermediates that produce the excited carbonyl fragments and simultaneously satisfy the experimental results in the present study. In this study, the substituent effect on the ring closure step in the oxy-Wittig type reaction was revealed by chemiluminescence decay. The promotion of the ring formation results in the... 

Ketenes also undergo nucleophihc reactions with phosphorous nucleophiles. In an application of the phospha-Wittig-Homer reaction fluorenyhde-... 

Phospha-Wittig-Horner type reactions are a common occurrence in the literature, and what follows is a listing of some of the most salient papers in the period considered by this review (2011-12). 

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