Alkylidene phosphoranes

Phosphoranes, alkylidene-. See Phosphonium,... Phosphoranes, (alkylideneazino)-. See Ketones, (triphenylphosphoranylidene)hydrazones Phosphoric acid, 4-chlorophenyl esten nucleoside coupling with, 217-218 —, esters (See also Nucleotides) ... 

The reaction of an alkylidene phosphorane 1 (i.e. a phosphorus ylide) with an aldehyde or ketone 2 to yield an alkene 3 (i.e. an olefin) and a phosphine oxide 4, is called the Wittig reaction or Wittig olefination reaction. ... 

The most common method for the generation of the metal alkylidene species seems to be a-elimination from an intermediate dialkyl-metal species. This procedure gives the most active catalysts. Above we mentioned the addition of other carbene precursors, which leads to active catalysts. Other methods to generate the metal alkylidene species involve alkylidene transfer from phosphoranes [16] or ring-opening of cyclopropenes [17], In Chapter 16.4 we will describe a few compounds that are active by themselves as metathesis catalysts. 

In contrast to the P=C bond of phosphaalkenes (Section 8.2.2), double bonds between phosphorus and a heteroatom have not been used much as dipolarophiles. Most of the studies reported so far were devoted to the reactivity of the (X )P=N bond of iminophosphanes. Amino(iminophosphanes) react with diazoalkanes to form 4,5-dihydro-3//-l,2,3,4-triazaphospholes or, by N2 loss from the latter, to imino(alkylidene)-X -phosphoranes (5,238). With P-halogeno-(arylimino)phos-phanes 174 and the appropriate diazo compounds, 3//-l,2,3,4-triazaphospholes 175 (167) and 176 (239) (Scheme 8.40) were obtained as the major products after cycloaddition and eliminative aromatization. 

A versatile protocol for the generation and cyclization of secondary radicals from hexo-pyranose sugars is shown in Scheme 3 [10], The Wittig reaction of reducing sugars with two eq of an alkylidene phosphorane readily provide hex-5-ene-l-ols, which were converted into hex-5-enyl radicals by the l-ff-imidazole-l-carbothioate. The cyclization reaction is carried out in refluxing benzene or toluene with tributyltin hydride and AIBN, according to... 

Alkylidene derivatives of phthalic thioanhydride are formed as shown in Scheme 160. Reaction of phthalic thioanhydride with hot triethyl phosphite produces trafts-S -bithioph-thalide (457), probably via the carbene and phosphorane (Scheme 161) (72AHC(14)331>. Support for this mechanism stems from the fact that brief treatment of phthalic thioanhydride with triethyl phosphite in the presence of phthalic anhydride gives (458) in the presence of benzaldehyde the same reaction leads to the benzylidene derivative (456). An alternative mechanism has also been suggested, in which the penultimate step is the formation of an epoxide, which is deoxygenated to yield the product (72AHC(14)331>. 

Following Schlosser (ref. 9), we divided the alkylidene phosphoranes (phosphorus ylides) 1. used in Wittig reactions into three groups according to their reactivity. 

The reaction of dienamines and sulfonyl azides provides a method for the synthesis of vinyldiazomethanes.233,431 Likewise, the pyrolysis of a fluo-rinated 1-benzyltriazoline over a nickel surface yields difluorodiazometh-ane.145 The formation of diazo compounds from the reaction of azides with alkylidene phosphoranes apparently originates from an intermediate triazoline compound (Scheme 145)408,411 412,415,441... 

Reactions of Aziridines, 4-Oxazolines, and Their Derivatives with Alkylidene Phosphoranes and Phosphorus(III) Nucleophiles... 

We have shown that the ylids 3 react with a number of nucleophiles (3). In particular 3a and 3b react quantitatively with the alkylidene phosphoranes 5 to give 3-pyrrolines 6a and 6b as a mixture of diastereoisomers. The cyclisation occurs via an intramolecular Wittig reaction on the carbonyl of an ester group (M. In the same conditions, 2c reacts with 5 to give quantitatively the pyrrolines 7c (two diastereoisomers) as a result of a Wittig reaction on the carbonyl of the keto group in 3c. 

However, the reactivity of g-ketophosphoranes 8 with R =Ph or Me is different from the alkylidene phosphoranes 5 owing to the double bond character of the C-g bond due to an important... 

C Nuclear Magnetic Resonance Spectra of Three Simple Alkylidene Phosphoranes ... 

Another attractive route to the synthesis of highly reactive tungsten carbene complexes involves alkylidene transfer from phosphoranes. Arylimido tungsten... 

The P—C bonds of 83 are essentially equivalent, suggesting contribution of polar forms. An extremely long P—O bond in contrast to 581 indicates open chain mesomeric structures, stable due to electron delocalization (60). At 125°C a Wittig reaction occurs, and 84 is formed (26). The same type of [2 + 2] cycloaddition has been found with a series of P-(chloro)alkylidene-phosphoranes. The oxaphosphetanes 83b-d thermally eliminate hydrogen chloride to yield vinyloxophosphoranes (165a). 

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

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