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The first example of 1,3-dipolar cycloaddition reactions of  C -aryl (or hetaryl)- N -phenylnitrones to monosubstituted ylidene malononitriles and 4-benzylidene-2-phenyl-oxazol-5(4 H )-one is described. The reaction of  C -(4-(dimethylamino)phenyl)- N -phenyl-nitrone  (1a)  with 2-(4-substituted-benzylidene)malononitriles  2a ,  b  in dry toluene, in the absence of catalyst, at reflux temperature furnished the novel cycloadducts 2-(3-aryl-2-phenyl-2,3-dihydro-1,2,4-oxadiazol-5-yl)-3-(4-methoxyphenyl)acrylonitriles  3a ,  b . Refluxing  C -aryl (or hetaryl)- N -phenylnitrones  1b–i  with 2-(4-methoxy-benzylidene)malononitrile ( 2a ) in dry toluene, in the absence of catalyst, gave the unexpected 2-cyano-3-(4-methoxyphenyl)-acrylamide ( 5 ), as the sole product. On the other hand, refluxing 4-benzylidene-2-phenyloxazol-5(4 H )-one ( 7 ) with an equimolar amount of  C -aryl (or hetaryl)- N -phenyl-nitrones  1a–c ,  f–i  in absolute EtOH afforded the previously unknown 5-anilino-4-benzoyl-2-phenyloxazole ( 10 ), as the only isolable product. The resulting products were formed with a high degree of regio- and stereoselectivity. Quantum chemical calculations were performed to verify stereoselectivity of the studied reaction. A mechanistic proposal is presented to rationalize the formation of these products.

zeitschrift für naturforschung b

Regio- and stereoselective 1,3-dipolar cycloaddition reactions of  C -aryl (or hetaryl)- N -phenylnitrones to monosubstituted ylidene malononitriles and 4-benzylidene-2-phenyloxazol-5(4 H )-one