Acid-Catalyzed Nitronate Cycloaddition Reactions. Useful Syntheses and Simple Transformations of 3-Acyl- and 3-Alkenylisoxazolines

Abstract

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. α-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-(α-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. © 1984, American Chemical Society. All rights reserved.