Oxidation of hydroxamic acids at room temperature in the presence of 2,5-dimethylfuran gives cis-1,4,2-dioxazolylbutenones (5), the structures of which have been confirmed by the synthesis of the dihydro-derivative (12) from the reaction of benzonitrile oxide with hexane-2,5-dione. If the oxidation is carried out at 0 °C good yields of the unstable furo[1,4,2]dioxazines (7), the formal products of the addition of the furan to the nitrosocarbonyl-arene or -alkane, can be isolated. Compounds (7) are the precursors to (5) and this isomerisation in the oxidation medium is essentially quantitative. It is probably catalysed by an unidentified component, since when pre-isolated (7) is heated the reaction is solvent-dependent and sometimes complex, the amounts of (5) formed being very variable. Nitrosocarbonylbenzene adds to the unsymmetrical compound 2-methyl-5-phenylfuran only at the 2,3-bond, giving the dioxazine (17) and thence the dioxazole (15) exclusively. Secondary amines add readily to the β-carbon of the enone group in (5) while tertiary amines, or more efficiently iodine, convert (5) into the trans-isomers (11)

The retro-reaction of (5c) at 80 °C to dimethylfuran and p-nitronitrosocarbonylbenzene has been demonstrated by trapping the latter, with 1,4-dimethyl-2,3-diphenylcyclopentadiene, as the adduct (21).