Benzonitriles, oxidative addition

The addition of benzonitrile oxide to acrylic acid gave only the 4-carboxylic acid (441) (59MI41601), while addition to cis- and trans-cinnamic esters gave cis and trans diastereomeric pairs of 4-carboxylic acids (442) (Scheme 100) (59MI41600). Arbisono repeated the experiment and, when methyl c/s-cinnamate was used, in addition to the 4-carboxylic acid some 5-carboxylic acid (442) was isolated (66MI41600). The reaction of vinyl bromides with benzonitrile oxide yielded only an isoxazole and not a bromoisoxazoline (Scheme 101) (78JCR(S)192). 

The addition of benzonitrile oxide to cyclooctatetraene produced a monoadduct which was induced to undergo valence tautomerism to produce a tricycloisoxazoline (Scheme 104). A similar reaction with tropone gave a minimum of eight adducts from which two monoadducts were isolated (Scheme 104) (70T5113). 

A variety of 1-azirines are available (40-90%) from the thermally induced extrusion (>100 °C) of triphenylphosphine oxide from oxazaphospholines (388) (or their acyclic betaine equivalents), which are accessible through 1,3-dipolar cycloaddition of nitrile oxides (389) to alkylidenephosphoranes (390) (66AG(E)1039). Frequently, the isomeric ketenimines (391) are isolated as by-products. The presence of electron withdrawing functionality in either or both of the addition components can influence the course of the reaction. For example, addition of benzonitrile oxide to the phosphorane ester (390 = C02Et) at... 

In the reaction of benzonitrile oxide (1,3-dipolar addition) with AyV -thiocarbonyldi-1,2,4-triazole the cyclic addition product has been isolated in 87% yield -170- ... 

As with other diazines, addition of benzonitrile oxide to pyridazines results in the formation of angular-fused tricyclic products C1995T11855, 1996T6421>. 

Bis-cycloadducts 169 and 170 (R = R1 =MeO, Me, Cl) obtained from reactions of respective 4-substituted benzonitrile oxides and pyridine have been described. Crossed adducts, such as 169 (R = H, R1 = MeO R = MeO, R1 = H), were also formed on treating pyridine with mixtures of various nitrile oxides (338). Addition of pyridine to benzoylcarbonitrile oxide affords an unstable... 

The same authors reported in a later study <2000H(3)69> that pyrazinone 340 is also a suitable starting material for a such transformation. The reaction proceeds in two steps the starting pyrazinone 340 when treated with benzonitrile oxide yields an addition product 341 which undergoes oxidative cyclization in the presence of iodine-potassium iodide to the ring-closed [l,2,4]oxadiazolo[4,5-tf]pyrazines 342. 

N-Sulfinylaniline, the procedure for the preparation of which is described in Part A, is a versatile intermediate in the synthesis of heterocyclic compounds. Benzohydroxamoyl chloride, the method for the preparation of which is given in Part B, is the precursor of the highly reactive benzonitrile oxide, the diverse dipolar addition reactions of which have been thoroughly investigated. A wide array of heterocyclic compounds can be prepared starting with benzonitrile oxide. ... 

Tetrakis(triethylphosphine)platinum(0) is extremely air sensitive and readily soluble in saturated aliphatic hydrocarbons. The complex can be stored under dry nitrogen in a freezer (-35°) for several months. The complex readily loses one of the coordinated phosphine molecules to give Pt(PEt3)36 (dissociation constant (K ) in heptane is 3.0 X 10" ). The H NMR spectrum measured in benzene-d6 shows two multiplets at 5 1.56 (CH2) and 1.07 ppm (CH3). Tetrakis-(triethylphosphine)platinum(O) is a strong nucleophile and reacts readily with chlorobenzene and benzonitrile to give a-phenyl complexes PtX(Ph)(PEt3)2 (X = Cl, CN).7 Oxidative addition of EtOH affords [PtH(PEt3)3] +. 

Other nitrile oxide cycloadditions have been reported including the addition of benzonitrile oxide to alkenes catalysed by a chiral vinyl dioxazaboiodne catalyst (the ee s ate moderate) <98TL8513> and the reaction ofi -phenylpyrazolylnitiile oxide with Ceo <99TL489>. ... 

In etherischer Losung erfolgt die Addition von Benzonitriloxid bzw. 3-Nitro-benzonitril-oxid an das dipolarophile Trinitro-acetonitril in guter Ausbeute143. 

The behavior of 2(3//)-furanones is completely different from that of the isomeric 2(5//)-furanones (27), which on addition of benzonitrile oxide (28) give the furoisoxazolines 29,30, and 31 (Scheme 8) (96T3457). 

Of the systems showing 1,3-dipolar reactivity, the nitrile oxide is possibly the longest known and is one of the most reactive.81,82 Such reactivity shows itself in the great variety of both acyclic- (via 1,3-addition) and heterocyclic structures (via 1,3-cycloaddition) that can be synthesized from them.59 In the reactions of nitrile oxides with terminal alkynes, both modes of reaction occur, leading to alkynyloximes (25) and isoxazoles (26). The former readily cyclize to the latter but have been detected or isolated in some cases.83,84 In some substituted alkynes 1,3-addition of a substituent may compete with cycloaddition of the triple bond. For example, the reaction between benzonitrile oxide and 3-aminopropyne gives a mixture of the 1,3-adduct (28) (ca. 40%), the 1,3-cycloadduct (29) (ca. 5%), and the product of both modes of reaction (30) (ca. 15%).85 Competition can also occur... 

Thus, with electron-rich or electron-poor monosubstituted alkenes, the reaction with tri-fluoroacetonitrile oxide is more regioselective than with benzonitrile oxides. and the oxygen of the nitrile oxide adds to the substituted carbon. With other dipolarophiles, cyeloaddition is less regioselective. Competitive reactions include an electrophilic addition on the nitrile oxide, in particular with 1,1-disubstituted alkenes. and a further cyeloaddition which can occur when the dipolarophile is used in excess. ... 

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