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本文系统总结了非对称氮杂环丁烷的区域选择性开环反应。氮杂环丁烷的开环反应主要包括亲核开环、Stevens重排扩环及消除开环反应等。其中,亲核开环反应是氮杂环丁烷的主要开环方式。开环的区域选择性与氮杂环丁烷取代基结构密切相关。氮杂环丁烷相对比较稳定,其开环通常需要路易斯酸催化或者先转化成季铵盐才可以发生,因此,其开环反应的区域选择性受电子效应的影响比较明显。邻位带有不饱和官能团的氮杂环丁烷及其季铵盐一般发生氮原子与带有不饱和官能团的碳原子之间化学键的断裂,这是因为如芳基、烯基、氰基、酰基、甲酸酯基和甲酰胺基等不饱和官能团的共轭效应可以稳定其连接的碳原子在开环时形成的过渡态或者中间体,使该C—N键更容易断裂。如亲核开环反应,亲核试剂一般进攻芳甲位、烯丙位或连有氰基或甲酸酯基或甲酰胺基的邻位碳原子,电子效应起主要作用。对于2-烷基取代的氮杂环丁烷及其季铵盐,大位阻或者亲核性强的亲核试剂的开环反应一般发生在位阻小的氮邻位碳原子,空间效应起主要作用。分子内的亲核开环反应主要受反应过程中环大小的控制,一般有利于经过三元环、五元环、六元环和七元环过程开环得到开环产物。氮杂环丁烷是一类非常重要的含氮杂环化合物,通过总结和分析氮杂环丁烷的开环反应及其区域选择性,可以更好地认识和利用这类反应,通过有效地预测和控制开环反应的方向,来制备所需的有机化合物。希望本文能够促进氮杂环丁烷开环反应在有机化学中的发展与应用。
This article systematically summarizes the asymmetric azetidine regioselective ring-opening reaction. Azetidine ring-opening reactions include nucleophilic ring opening, Stevens rearrangement ring expansion and elimination ring-opening reaction. Among them, the nucleophilic ring-opening reaction is the main open-loop method of azetidine. The ring-opening regioselectivity is closely related to the azetidine substituent structure. The azetidine is relatively stable. The ring opening usually takes place by the Lewis acid catalysis or the first conversion to the quaternary ammonium salt. Therefore, the regioselectivity of the ring opening reaction is more affected by the electron effect. The azetidine and its quaternary ammonium salt having an unsaturated functional group in the ortho position generally undergo cleavage of the chemical bond between the nitrogen atom and the carbon atom having an unsaturated functional group because the aryl group, the alkenyl group, the cyano group, The conjugation effect of unsaturated functional groups such as acyl groups, formate groups and formamido groups can stabilize the C-N bond more easily by cleaving the transition state or intermediate formed when the carbon atom to which it is attached at the ring opening. Such as the nucleophilic ring-opening reaction, the nucleophiles generally attack aromatic aryl, allylic position or even with a cyano or formic acid ester group or ortho-carbon atom, the electronic effect plays a major role. For 2-alkyl-substituted azetidine and its quaternary ammonium salts, the ring-opening reaction of a sterically bulky or nucleophilic nucleophile generally occurs at a sterically hindered nitrogen ortho-carbon atom. The steric effect main effect. The nucleophilic ring-opening reaction in the molecule is mainly controlled by the size of the ring in the reaction process, which is generally conducive to ring-opening of the product after three-ring, five-ring, six-ring and seven-ring ring opening. Azetidine is a very important class of nitrogen-containing heterocyclic compounds. By summarizing and analyzing the ring-opening reaction of azetidine and its regioselectivity, this kind of reaction can be better understood and utilized. By effectively Predict and control the direction of the ring-opening reaction to prepare the desired organic compound. We hope this article can promote the development and application of the azetidine ring-opening reaction in organic chemistry.