Cycloaddition of a-nitrosostyrene (1 a) to several substituted styrenes is shown to give 3-phenyl-5,6dihydro-4H-l,2-oxazines (2) in moderate yield. Reactions with 4-nitro-a-nitrosostyrene (1 b) give better yields of the corresponding adducts (3). The preferred conformations of the adducts are deduced from their n.m.r. spectra. The observed regio-and stereo-selectivities of the additions are interpreted in terms of a one-step addition in which the olefins act as the donor components.The first example of a formal 1,3-dipolar addition of a vinyl nitroso compound is provided by the formation of the nitrone (5) as a minor product of the reaction of a-nitrosostyrene with 2-methoxypropene. The relative yield of this nitrone is not increased by the change to a more polar solvent, nor by the use of tc-bromoacetophenone anti-oxime in place of the usual syn isomer as the precursor of a-nitrosostyrene. It is suggested that this, and other minor products (4) isolated from the cycloadditions, may be formed because of steric inhibition of the usual Diels-Alder-type process.* Preliminary experiments were carried out by Dr. G. M. Iskander.

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Die aus den Oximen (I) gebildeten Vinylnitrosoverbindungen (II) reagieren mit zahlreichen Olefinen bzw. ungesättigten Verbindungen (III) bzw. (VI) unter Bildung der Cycloaddukte (IV) [(IVb) entsteht im 87: I3‐Gemisch (Ausb.‐Angabe in Klammern) mit seinem 5,6‐Regioisomeren], (V) bzw. (VII).

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