[3+2] Cycloadditions [32CA] involving nitrones as 1,3-dipolar species to alkenes yield isoxazolidines, which on further transformations can be converted to naturally occurring bioactive compounds. Thus the 32CA route provides conversion of simple natural products to more complex natural occurring bioactive nitrogen heterocycles, and close analogues. The present work deals with 32CA between the nitrones C-(1-naphthyl)-N-methyl nitrone and C-phenyl-N-benzyl nitrone to
α,β-unsaturated carbonyl compounds as dipolarophiles, viz. arylidene malonate esters, methyl cinnamate and benzylidene acetophenone (chalcone). Methyl cinnamate is a naturally occurring compound, while the chalcone scaffold is present in several natural products. Structure elucidation of the generated cycloadducts have been achieved by means of detailed spectroscopic and XRD studies. All the cycloadditions investigated occurr regioselectively to yield tetra/penta-substituted isoxazolidines, where the carbonyl group(s) are situated at the 4-position of the isoxazolidine ring. DFT computations including optimised geometries, FMO energies, electronic chemical potentials, chemical hardness, chemical softness and reactivity indices of a number of the reactants have been calculated at DFT/B3LYP/6-31++G(d,p) level of theory. The calculated reactivity indices have been used to analyse the 32CAs studied and to predict the regioselectivities; the predictions are in excellent accord with the experimental results.

中文翻译：

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[3 + 2]环加成。第三十三部分 C-（1-萘基）-N-甲基硝酮和C-苯基-N-苄基硝酮对α，β-不饱和羰基化合物的选择性环加成1,2

[3 + 2]环烯加成化合物[32CA]涉及作为烯烃的1，3-偶极物种的硝酮，生成异恶唑烷，经进一步转化，该异恶唑烷可转化为天然存在的生物活性化合物。因此，32CA途径可将简单的天然产物转化为更复杂的天然存在的生物活性氮杂环和类似物。与32CA本工作涉及的硝酮之间Ç - （1-萘基） - ñ -甲基硝酮和Ç苯基Ñ -苄基硝酮，以
α，作为dipolarophiles，β不饱和羰基化合物即。亚芳基丙二酸酯，肉桂酸甲酯和亚苄基苯乙酮（查耳酮）。肉桂酸甲酯是天然存在的化合物，而查耳酮骨架存在于几种天然产物中。借助于详细的光谱学和XRD研究已经阐明了生成的环加合物的结构。研究的所有环加成均选择性发生，以产生四/五取代的异恶唑烷，其中羰基位于异恶唑烷环的4-位。在理论上以DFT / B3LYP / 6-31 ++ G（d，p）的水平计算了DFT计算，包括优化的几何形状，FMO能量，电子化学势，化学硬度，化学柔软度和许多反应物的反应指数。计算出的反应指数已用于分析所研究的32CA，并预测区域选择性。该预测与实验结果非常吻合。