Changing the mechanism of the widely used 1,3-dipolar cycloaddition reaction from its usual asynchronous one-step pattern to the rarely observed stepwise form leads to the emergence of intermediates, side products, and other impurities. Thus, it is crucial to determine the nature of the mechanism of the 1,3-dipolar cycloaddition reaction between a special 1,3-dipole and a specified dipolarophile (by theoretical methods) before using them for synthesizing a desired product. In this study, therefore, we have investigated the possibility of some probable intermediates emergence in the 1,3-dipolar cycloaddition reaction between cyclobutadiene and thioformaldehyde S-oxide. The results showed that emergence of Int (B) (−52.1 kcal mol−1) via transition state (B-1) is favorable both thermodynamically and kinetically (in comparison with all other stepwise routes). That is, developing probable impurities should not be neglected at least in the cases of the reactions between some thioformaldehyde S-oxide and some dipolarophiles.

中文翻译：

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了解硫代甲醛 S-氧化物和环丁二烯之间 1,3-偶极环加成反应的机制：逐步和协同路线之间的竞争

将广泛使用的 1,3-偶极环加成反应的机制从其通常的异步一步模式更改为很少观察到的逐步形式导致中间体、副产物和其他杂质的出现。因此，在使用特定的 1,3-偶极和特定的偶极亲和试剂（通过理论方法）合成所需产品之前，确定 1,3-偶极环加成反应机制的性质至关重要。因此，在本研究中，我们研究了在环丁二烯和硫代甲醛 S-氧化物之间的 1,3-偶极环加成反应中出现一些可能中间体的可能性。结果表明，Int (B) (-52. 1 kcal mol-1) 通过过渡态 (B-1) 在热力学和动力学上都是有利的（与所有其他逐步路线相比）。也就是说，至少在某些硫代甲醛 S-氧化物与某些亲偶极体反应的情况下，不应忽视产生可能的杂质。