Phosphoryl carbenes

Among the very rare phosphinocarbenes that undergo dimerization are the (phosphino)(phosphoryl)carbenes 2r. Two examples of direct head-to-tail dimerization leading to the corresponding 1 A5,3A5-disphosphetes 73i2 have been reported and occur as a result of the multiple bond character of transient carbenes 21 2.77... 

The stereochemistry of the cyclopropanation reactions is difficult to predict. (Dimethoxy-phosphoryl)carbene reacts stereospecifically with ( )-l,2-diphenylethene to give 3-dimethoxy-phosphoryl-/ra .v-l,2-diphenylcyclopropane. In contrast, photolysis of (dimethoxyphosphor-yl)(phenyl)diazomethane in the presence of (Z)-but-2-ene gave a mixture of diastereomeric m-isomers, (la,2, 3 )-2 and (la,2a,3a)-2, along with the /ranj-isomer, (la,2ot,3/ )-2, in 15, 3 and 5% yield, respectively. Reaction with ( )-but-2-ene afforded only two of the possible cyclopropanes, namely (la,2, 3 )-2, and (Ia,2a,3/S)-2. ... 

Fused cyclopropanes are obtained by intramolecular cyclopropanations or by intermolecular reactions with cyclic alkenes or aromatic derivatives. The phosphoryl carbenes are the only phosphorus-substituted carbenes used in these reactions. 

It is possible that the isomerization mechanism involves the generation of (dimethoxyphos-phoryl)carbene which reacts with l,3-bis(trifluoro)benzene under thermodynamic control to give the cyclopropane 7. As proof, starting from the kinetic isomer 5, the transient phosphoryl-carbene was trapped by cyclohexane to yield the corresponding C-H insertion product. 

The year s reviews cover phosphorylated indoles, phosphorus-selenium compounds, phosphoryl carbenes, phosphorus-sulphur compounds, and steroid phosphates, as well as the synthesis of phosphorus esters via oxyphosphoranes. A review on phosphonates contains many interesting applications of some of the well-tried syntheses of these as analogues of natural phosphates. ... 

Four-membered P.O-heterocycles 31 were obtained from [2 + 2]-cycloaddition of carbonyl compounds to phosphorylated carbenes generated from a-diazabenzyl-phosphine oxide under thermal- or photoinitiation (Scheme 16) [32-34], 2-Oxo-l,2-... 

The dialkyl (triarylmethyl)phosphonates 35 seemed to be likely contenders for P—C bond cleavage on photolysis however, the first step in such treatment is evidently the formation of a phosphorylated carbene together with that of a biaryl in the presence of an alcohol, the ethers 36 are produced in moderate yields with no cleavage of the phosphorus-carbon bond ° . ... 

Phosphoryl carbenes can be prepared from the corresponding diazo compounds they rearrange readily to methylene phosphene oxides . ... 

Irradiation of 7 in methanol gives a quantitative yield of a-methoxyphosphine oxide 18a il,14) however, when the same carbene (16a) is generated by thermolysis of 7 in ethanol then rearrangement to 17 a also takes place 15). In view of the behavior of 16a, para substituents in the phenyl groups of the phosphoryl group influence the rearrangement only if they exert a promoting effect. Thus it is understandable that... 

Welter, W., Hartmann, A., and Regitz, M., Isomerization reaction of phospho-ryl-vinyl-carbenes to phosphorylated cyclopropenes, acetylenes, indenes, and 1,3-butadienes, Chem. Ber., Ill, 3068, 1978. 

The (phosphino)(silyl)carbene 2a readily and cleanly adds to benzalde-hyde and cinnamaldehyde, affording the oxiranes 27 and 28, as single diaste-reomers.40 These results strongly suggest a concerted mechanism, since the formation of a zwitterionic intermediate, such as 29, would result in the formation of a phosphoryl alkene via oxygen atom attack at the phosphorus center. Note that 2a does not react with ketones, which is in line with its nucleophilic character. 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

Nolan and co-workers have extended the scope of transesterification reactions to include phosphonate esters as phosphorylating agents [137]. In this publication the authors use dimethyl methylphosphonate 273 and benzyl alcohol with a variety of imidazolylidene carbenes (Table 23). The nse of molecnlar sieves to absorb methanol leads to increased conversion however, longer reaction times lead to decreased... 

Phosphino(silyl)carbenes and phosphoryl(silyl)carbenes. 761... 

Alkoxycarbonyl- E5, 711 7-(Diazo-phosphoryl-methyl)- E14b, 1353 (Ag - Aryl) E19d, 641 (Diazomethylierung) 7-Methoxycarbonyl- E18, 1006 (Carben + Benzol)... 

As shown by competition experiments using hex-1-ene and acrylonitrile as substrates (Tables 1 and 2), the electro/nucleophilicity of phosphorus-substituted carbenes can be dramatically altered with the substituents, from the weakly electrophilic dimethoxyphosphoryl(phenyl)methyl to the highly nucleophilic [methoxy(sodiooxy)phosphoryl](phenyl)methyl. This control is of primary interest in extending the scope of accessible cyclopropanes. 

Transient phosphoryl-substituted carbenes, generated by photolysis or by copper catalysis, react selectively with one double bond of a 1,3-diene affording mixtures of trans- and c -isomers which, in some cases, can be separated by column chromatography on silica gel or by distillation (Table3). ... 

In the same way, phosphoryl-substituted carbenes reacted selectively with one double bond of an allene to give cyclopropane 1 no yield was reported. ... 

Maas, G., and Regitz, M., Carbenes. Part 10. Substituent dependence of the norcaradiene/cycloheptatriene-equitibrium investigated in 7-phosphoryl- and7-carbonylsubstituted systems, Chem. Ber, 109,2039,1976. 

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