From nitrile oxides

The addition of hydrogen chloride to nitrile oxides VII produces hydroxamoyl chlorides in high yield However, this method is only of 

Hydroxamoyl chlorides from nitrile oxides. General procedure ( ). To a solution of 0.01 mole of the corresponding nitrile oxide in 10 ml of methylene chloride and 5 ml of anhydrous diethyl ether, excess hydrogen chloride is added with ice-cooling. Evaporation of the solvents under vacuum, and recrystallization from benzene/ligroine affords the hydroxamoyl chlorides, usually in high yield. 

The reaction of cyanogen-di-N-oxide (VIII) with hydrogen bromide in glacial acetic acid has been used as a quantitative analytical method ( ), and aqueous hydrochloric or hydrobromic acid can be added to afford the corresponding dihalide (IX) 

The parent hydroxamoyl chloride X was obtained by heating salts of fulminic acid XI with dilute hydrochloric acid ( ). 

The hydroxamoyl chloride X is stable at 0°C for some time, but upon warming rapid decomposition occurs, with formation of hydroxylamine hydrochloride ( ). This hydroxamoyl chloride is a lachrimator and vesicant, and it causes severe headaches therefore, it should be handled with caution ( ). 

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Finally, the condensation of unsaturated compounds with fulminates known as the fulminic synthesis represents the simplest case of synthesis from nitrile oxides. Barnes has reviewed in detail the work carried out up to 1953 thus we shall be concerned here only wdth more recent publications or those of general interest. 

The experimental conditions for the syntheses starting from acid chlorides of hydroxamic acids and from nitrile oxides are somewhat different. In the former case the other component of the reaction is organometallic, usually an organomagnesium derivative of an acetylene or, less frequently, a sodium enolate of a /8-diketone. Nitrile oxides condense directly with unsaturated compounds. 

The general synthetic scheme starting from nitrile oxides, which condense with acetylenes to yield isoxazoles and with olefins to yield A -isoxazoIines may be represented by Eqs. (1) and (2). The forma-... 

The mechanism is thought to be analogous to that suggested for the formation of 1,3,5-benzoxadiazepines from nitrile oxides and 2-phenylbenzazete (see Section 4.2.1.4.2.1.). 

The thione group of dithiazolethiones is a very reactive heterodipolarophile. In Scheme 18 are given cycloadditions with nitrile oxides <67BSF2239>, diphenylnitrilimine, and ethyl azidoformate <85JCS(P1)1205>. The primary adducts are spiro derivatives, but only compound (131), which is obtained from nitrile oxides is isolable at low temperature. All are decomposed to give respectively compounds (132)-(134) and occasionally nitriles and sulfur. Compound (134) reacts further with nitrilimine affording compound (135) which is also isolated. 

Talaromycin B is a spiro-acetal produced by the fungus Talaromyces stipitatus, the toxicity of which may be due to its ability to block outward potassium fluxes. In an elegant synthesis, the requisite open-chain polyol with hydroxy groups in the y-and y -positions was assembled from nitrile oxide and olefin building blocks 50 and 51, both of which carry a f>w(hydroxyethyl) moiety protected as a cyclohexanone acetal (284). Hydrogenolysis of the N O bond of isoxazoline 52 using Raney nickel, followed by treatment with aqueous acid, gave the spiroketal 53, which was further transformed into racemic talaromycin B (54) (Scheme 6.54) (284). 

Several processes to prepare oxadiazoles start from nitrile-oxides or their precursors, hydroxamyl chlorides. Aromatic nitrile oxides are obtained by treating the corresponding hydroxamyl chlorides with... 

Here, isoxazole-3-carboxylic acid (IV)-the main product of the reaction-is formed from nitrile oxide (III) on adding acetylene to it. 

Azine approach. Acid-catalyzed cyclization of 2-/3 -oxoalkylpyridine 1-oxides (37) constitutes a general method for the preparation of the isoxazolo[2,3-a]pyridinium ring system (77JOC1364). By analogy to the synthesis of isoxazoles from nitrile oxides, the oxo chain should be replaceable by an alkynyl or ethenyl chain, the latter containing a substituent which can readily be eliminated from the cyclic product. 

D. Hoppe, Angew. Chem., Int. Ed. Engl. 13, 789-804 (1974). Syntheses from nitrile oxides ... 

A very significant contribution to the development of isoxazole chemistry came in the period 1930-1946 from Quilico s studies on synthetic approaches to the ring system from nitrile oxides and unsaturated compounds <19300172, 1950NAT226>. However, the study of isoxazolidines began very much more recently being related to the availability of this nucleus and then to the discoveries of cycloadditions of nitrones to olefins <1960TL9> and intramolecular cyclizations of unsaturated nitrones <1959JA6334>. 

Arenecarbonitrile oxides, generated by the joint action of acetyl chloride and sodium methox-ide on arylnitromethanes,7 react with symmetrical diaroylmethanes to yield transient 2/7-aziri-nes, which add a second molecule of the nitrile oxide to form 5-aroyl-3,6-diaryl-4//-1,2,4-oxa-diazines 1. The suggested course of the reaction is supported by the observation that 1,2,4-oxadiazines are formed from nitrile oxides and isolated azirines.8... 

Carbodiimides. Formation of carbodiimides from selenoureas is observed on reaction with NaI04 in DMF. The selenoureas are obtained from nitrile oxides and se-lenonoamides. 

Oxidation of nitrile oxides. A simple access to 0=N-C0R from nitrile oxides is the addition of NMO in a dichloromethane solution at room temperature. The reactive acyl nitroso compounds are trapped (usually with dienes). 

In the presence of magnesium ions, syn-isoxa-zolines, e.g. 9, are formed selectively from nitrile oxides and chiral terminal allylic alcohols such as CH2=CHCHEtOH (94JA2324). The cycloadduct 12 of dichloromesitonitrile oxide... 

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