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Nitronic esters derived from primary nitro ketones, ethyl nitroacetate, and (phenylsulfonyl)nitromethane react with dipolarophiles in the presence of nonaqueous protic and Lewis acids to give nitrile oxide cycloadducts. a-Nitro ketones, ethyl nitroacetate, and (phenylsulfonyl)nitromethane give nitrile oxide cycloadducts in the presence of p-toluenesulfonic acid, although conditions are necessarily more vigorous. The anions of phenylnitromethane and 1-nitropropane react similarly under mild conditions, the latter in poor yield. The methyl nitronic ester of (phenylsulfonyl)nitromethane undergoes direct cycloaddition to 1-hexene in neutral media to give diastereomeric isoxazolidines. 3-(a-Hydroxyalkyl)isoxazolines are readily prepared by reduction of 3-carbethoxyisoxazolines with sodium borohydride and by carbonyl addition to 3-acylisoxazolines with alkyllithium reagents. 3-Alkenylisoxazolines, which can be prepared from either 3-(hydroxyalkyl)isoxazolines or 3-sulfonylisoxazolines, undergo reversible [4 + 2]-cycloaddition with tetracyanoethylene.The diverse reactions of nitro compounds, nitronate salts, and nitronic esters with aqueous acid have been under study for over a century.1 Aldehydes and ketones are most commonly obtained (the Nef reaction). Under strongly acidic conditions, hydroxamic acids are formed instead; these may further hydrolyze to carboxylic acids and hydroxylamine (the Meyer reaction). Hydroxamic acid formation has been shown to proceed through hydrolysis of a nitrile oxide intermediate.2 Surprisingly little synthetic use has been made of this demonstration. Furoxans (1,2,5-oxadiazole 2-oxides) have been prepared from several nitro compounds under strongly acidic conditions,3 but extensive studies of nitrile oxide cycloadditions to added dipolarophiles are conspicuously lacking.