Benzonitrile ylide

Photolysis of 2,3-diphenyl-A -azirine (442) generates benzonitrile ylide (443). Irradiation in the presence of ethyl cyanoformate resulted in a mixture of the oxazoline (444) and the imidazole (445) by 1,3-dlpolar cycloaddition to the carbonyl and nitrile group, respectively (72HCA919). 

TABLE 7.1. ABSORPTION SPECTRA FOR SUBSTITUTED BENZONITRILE YLIDES... 

Irradiation of 3-phenyl-2H-azirines (2) with triphenylvinylphosphonium bromide (3) in acetonitrile forms 2H-indoles (4) (equation 3)29. The probable mechanism of formation of 4 leads, via benzonitrile ylide and 1,3-dipolar cycloaddition, to the C C double bond of the vinylphosphonium bromide via the assumed intermediate (5). 

Similarly, benzonitrile ylide (38) was obtained by photolysis of 3-phenyl-2H-azirine at 8K and characterized by its IR spectrum (vmax 1930 cm-1) (Eq. 12).49... 

Several three-membered ring nitrogen heterocycles, such as azirines, aziridines, di-aziridines and oxaziridines, undergo [3+2] cycloaddition reactions with isocyanates. For example, irradiation of 3-phenyl-2//-azirines 363 affords the benzonitrile ylides 364 which react with aryl isocyanates to give the oxazolines 365, resulting from addition across the C=0 bond of the isocyanate... 

Bravo et al. studied the reaction of various ylides with monooximes of biacetyl and benzil. Dimethylsulfonium methylide and triphenylarsonium methylide gave 2-isoxazolin-5-ol and isoxazoles, with the former being the major product. Triphenylphosphonium methylide and dimethyloxosulfonium methylide gave open-chain products (Scheme 135) (70TL3223, 72G395). The cycloaddition of benzonitrile oxide to enolic compounds produced 5-ethers which could be cleaved or dehydrated (Scheme 136) (70CJC467, 72NKK1452). 

The reaction between benzylidenetriphenylphosphorane and benzonitrile has been reinvestigated and the primary product (82) isolated. Stable ylides react similarly with activated nitriles, e.g. cyanogen and trifluoro-acetonitrile, but cyanomethylenetriphenylphosphorane with methyl cyano-formate gave largely the vinyl ether (83), the product of a normal olefin synthesis on the carbonyl of the ester group. 

This reaction may be visualized as proceeding by nucleophilic attack of tervalent phosphorus at the carbonyl group to give an intermediate such as (15). The structure of (16) was deduced from the fact that it was hydrolysed to the known phosphine oxide (17). Methylenephosphoranes (phosphorus ylides) may also be converted into monophosphazenes by reaction with benzonitrile ... 

Hynninen and coworkers <99JCS(PT1)2403> used a similar approach to prepare phytochlorin-C6o diad 38 (Scheme 11). The protocol employed the pyrolysis of the natural chlorophyll a molecule 35, followed by transesterification and demetallation to furnish derivative 36. Subsequent oxidation of 36 with OsCU and NaI04 has allowed the synthesis of the formyl derivative 37, which was further used as precursor of the azomethinic ylide intermediate in the 1,3-DC reaction with Cm leading to the formation of diad 38. Photochemical studies revealed that this diad underwent a fast intramolecular photoinduced electron transfer in polar solvents such a benzonitrile <99JACS9378>. 

The 1,3-dipolar cycloadditions of benzonitrile oxides with tertiary cinnamides yield the 5-phenyl and 4-phenyl regioisomers in a reversal of the expected regioselectiv-ities shown with methyl cinnamate. Calculations have shown that steric factors are responsible for this reversal of regioselectivity." The 1,3-dipolar cycloadditions of benzonitrile oxide with electron-rich and electron-poor dipolarophiles are accelerated by sodium dodecyl sulfate micelles. Phenyl nitrile ylides react with electron-deficient alkenes to produce five-membered -heterocycles where measured rate constants are between 4 x 10 and 7 x 10 lmoP ... 

Cyanides can react with 1-aminopyridinium salts to give 2-substituted triazolopyridines, possibly via the pyridinium ylide. With 1-aminopyridinium iodide and cyanide ion the intermediate 4-cyanopyridine reacts with the aminopyridinium salt to give 2-(4-pyridyl)triazolopyridine (45).51 When acetonitrile or benzonitrile are used, 2-methyl- and 2-phenyltriazolo-pyridines are obtained.58 60 The reaction is thought to involve a dipolar cycloaddition of the N- mi nopyridine with the nitrile, as shown in Eq. (4). 

Supercritical carbon dioxide with a minute co-solvent addition is an effective medium for the 1,3-dipolar cycloaddition of azomethine ylides with DMAD to produce substituted pyrroles.67 The 1,3-dipolar cycloaddition of nitrile ylides [e.g. benzonitrile (4-nitrobenzylide) and 4-nitrobenzonitrile(benzylide)] with acrylamides provided a synthesis of 3,4-dihydro-2//-pyrroles with moderate to good yields.68 The Pt(II)-or Au(III)-catalysed 3 + 2-cycloaddition of the transition metal-containing azomethine ylide (63) with electron-rich alkenes provided a carbene complex (64), which yields tricyclic indoles (65) having a substituent at 3-position (Scheme 17).69 The 1,3-dipolar cycloadditions of azomethine ylides with aryl vinyl sulfones are catalysed by Cu(MeCN)4C104-Taniaphos with nearly complete exo- selectivity and enantioselec-tivities up to 85% ee.10 The 3 + 2-cycloaddition of benzol/>]thiophene 1,1-dioxide... 

The potential of laser flash photolysis in the study of carbene reactions with heteroatoms has come to be recognized in recent years. A number of kinetic studies using this technique have been carried out with carbene precursors in nitrile solvents.122-127 An absorption band at 470 nm was observed in the laser flash photolysis of diazofluorene (246) in inert solvents. This band was assigned to triplet fluorenylidene (247). In acetonitrile, however, a second band was also detected at 400 nm and whose buildup is concurrent with the decay at 470 nm.122 Laser flash experiments in other nitrile solvents (i.e., benzonitrile and pivalonitrile) also produced a transient absorption band which is very similar to that observed in acetonitrile. The band at 400 nm was assigned to an intermediate nitrile ylide (248). This absorption could be quenched on addition of an electron-deficient olefin providing good support for its... 

Oxazoles of various substitution patterns are well known heterocycles for which a number of methods of synthesis have been reported.129 Acyl carbenes or functionally equivalent species have been found to undergo cyclization with nitriles to give oxazoles in high yield via nitrile ylide intermediates.130,131 This reaction can be induced to occur under thermal, photolytic, or catalytic conditions.129,132,133 Huisgen and coworkers were the first to study this process in some detail.132 Thermolysis (or copper catalysis) of a mixture of ethyl diazoacetate and benzonitrile resulted in the formation of oxazole 254. The isolation of this product is... 

In a somewhat similar manner, diazodicyanoimidazole (260) was found to give the fused heterocycle 262 when heated in benzonitrile.141 This reaction presumably involves the intermediacy of nitrile ylide 261. 

The reaction of the cyclopropyl ylide (100) with benzonitrile oxide gave the oxazaphosphole (101) in 61% yield.51 Pyrolysis of 101 at 100°-110° (0.1 torr) gave an 84% yield of the relatively stable spiro-azirine (102). 

In another example of heterocyclic ring synthesis, pyridinium salts 816 require only Et3N for deprotonation, the resulting ylides 817 add to esters of 2-bromo-2-alkenecarboxylic acids or analogous benzonitriles to give intermediate betaines 818 which, via intramolecular nucleophilic attack, give indolizines 819 (Scheme 174) <1999JOC7618>. 

Many arsinimines are stable solids, handleable in air as in the case of arsonium ylides, the presence of electron-withdrawing substituents on the nitrogen atom increases their stability. When heated, N-benzoyltriphenylarsinimine decomposes to give triphenylarsine oxide and benzonitrile . 

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