Wittig, phospha

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. 

Subsequently, following the successful isolation of stable phosphaalkene-con-taining polymers 156, the use of the same substituent for the preparation of a related polymer featuring P=P moieties was attempted. It is known that dipho-sphenes M can be prepared by dimerization of transient phosphinidenes J generated by photolysis of phospha-Wittig reagents L (Scheme 4.43) [80e]. Photolysis at room temperature or thermolysis (neat, 250 °C, 2 min) of bifunctional compound 155 does indeed result in the formation of polymer 157 in near quantitative yield (Scheme 4.43) [80d], This soluble material was characterized by NMR spectroscopy and GPC analysis, which revealed a rather low molecular weight (Mn = 5900). The UV-Vis spectrum of 157 shows a jt-jt transition (435 nm) accompa-... 

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... 

Reactive 17 -phosphaalkene tungsten complexes such as 66, which are accessible by the phospha-Wittig route, are appropriate candidates for cycloadditions, as illustrated in Scheme 16.20 22... 

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... 

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). 

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. ... 

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. ... 

Masuda, J.D., Jantimen, K.C., Ozerov, O.V. et al. (2008) A lanthanide phosphinidene complex synthesis, structure, and phospha-Wittig reactivity. Journal of the American Chemical Society, 130, 2408. 

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. ... 

It has been shown that oxiranes can replace 1,2-dihaloalkanes in the synthesis of phosphiranes, provided that appropriate anionic RP reagents are used. The first example was described by Yoshifuji et al. (Equation (54)) <85CL44l>. Subsequently, it has been shown by Marinetti et al. that the so-called phospha-Wittig reagents transform oxiranes into phosphiranes with an inversion of configuration at carbon (Scheme 19) <92Sl57,93OM1207). Decomplexation by 1,2-bis(diphenylphos-phino)ethane is easily achieved in the molybdenum series. Optically active phosphiranes are readily accessible by this route. 

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-... 

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. ... 

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

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