Synthesis and Properties of Azoles and Their Derivatives. XLIII. Regio- and Stereoselectivity of [2+3] Cycloaddition Reaction of

E--Nitrostyrene (1) reacts with Z-C-aryl-N-phenylnitrones (2a–h) exclusively to give trans- and cis-2,5-diphenyl-3-aryl-4-nitroisoxazolidines (3a–h, 4a–h) in high yield. The molar ratio of trans and cis stereoisomers is affected by substituent in phenyl ring of the parent nitrone (2c) The reaction is found by AM1 calculations to be controlled by the in-teractions of the HOMO of nitrone with the LUMO of nitrostyrene. Key words: nitrones, nitroalkenes, [2+3] cycloaddition, regioselectivity Recently, the thermal [2+3] cycloaddition of nitrones to alkenes has found con-siderable application in organic synthesis [1–3]. Isoxazolidines formed in this reac-tion has attracted the attention of chemists, as they are valuable intermediates for the regio and stereocontrolled synthesis of some class of compounds of biological inter-est [2–4]. Despite that, few papers have been published on the utilization of ni-troalkenes in this reaction. A comprehensive review can be found in [5]. Therefore, continuing our study on the behavior of conjugated nitroalkenes towards 1,3-dipoles [6–8], the reaction of E--nitrostyrene 1 with Z-C-aryl-N-phenylnitrones 2a–h has been examined (Scheme 1). It is generally accepted that nitrone [2+3] cycloadditions occur according to con-certed mechanism [1,2]. Cis-trans isomerism observed usually in the cycloadducts concerns the substituents at positions C3 and C5, and is a simple consequence of su-pra-supra facial approach of the reactants in the transition state in an exo or endo manner. Because in both cases two regioisomers are possible the reaction of 1 with 2a–h theoretically should lead to the mixtures of regio and stereoisomeric nitro-isoxazolines 3a–h – 6a–h. The aim of the present study was to determine the true re-action regio and stereoselectivity