Nitrile oxides furoxan thermolysis

Few reactions of sulfonylfuroxans with olefins have been reported. Depending on the substituents at the furoxan ring, nature of dipolarophile, and temperature, different types of products may be obtained. It is relatively simple to cyclore-vert disulfonylfuroxans to a-sulfonyl nitrile oxides on thermolysis (81TL3371, 85T727). These nitrile oxides were trapped by dipolarophiles to yield sulfonyl-substituted isoxazole derivatives. For example, 3,4-bis(phenylsulfonyl)furoxan reacts with an excess of styrene in xylene under reflux to afford the corresponding isoxazoline 290 (Scheme 189). 

The type of the thermolysis process depends on the nature of the acyl group. Thus, other types of thermolysis processes involve reversible fragmentation of the furoxan ring to give two molecules of the corresponding nitrile oxide followed... 

The major fragmentation in mass spectra of 1,2,5-oxadiazoles is attributed to the loss of nitrile and nitrile oxide or expulsion of NO. The conversion of 3,4-dicyano-l,2,5-oxadiazole-2-oxide (3,4-dicyanofuroxan) 10 to cyanogen iV-oxide 11 (Equation 5) was investigated under the conditions of collisional activation (CA) and neutralization-reionization (NR) mass spectrometry. Flash vacuum thermolysis mass-spectrometry (FVT-MS) and flash vacuum thermolysis infra-red (FVT-IR) investigations of furoxans 10, 12, and 13 reveal that small amounts of cyano isocyanate accompany the formation of the main thermolysis product 11 <2000J(P2)473>. 

Stable furoxans are convenient starting compounds for generating short-lived nitrile oxides XCNO (X = ONC, NC, Cl, Br, and Me) by thermolysis (10, 11, 80, 81). The thermolysis of benzotrifuroxan (200°, in excess PhCN) proceeds (Scheme 1.6) with the cleavage of the C-C and 0-N(0) bonds in only one furoxan ring to give bifuroxan bis(nitrile oxide). The latter undergoes further reactions such as cycloaddition with PhCN or conversion to bisisocyanate (82). 

During thermolysis diacylfuroxans are transformed into the /V-oxides of a-keto nitriles, which form cyclic adducts in situ with various dipolarophiles [525], This method was used for the production of 4-nitro-3-(2-acetoxybomyl-2-carbonyl) isoxazole (yield 50%) by boiling bis(2-acetoxybomyl-2-carbonyl)furoxan with an excess of trans-/)-dimethylammonitroethene in toluene (Scheme 84). 

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