非对称氧杂环丁烷的选择性开环

Selective Ring-Opening reactions of Unsymmetric Oxetanes

氧杂环丁烷的开环反应主要包括亲核性开环、亲电性开环、自由基开环、酸催化和还原开环等几大类。本文主要总结了非对称氧杂环丁烷开环反应的区域选择性。非对称氧杂环丁烷开环反应的区域选择性主要受空间效应和电子效应的影响。氧杂环丁烷的开环反应以亲核性开环为主,强亲核性亲核试剂的开环,受空间位阻控制,主要进攻氧杂环丁烷位阻小的氧邻位碳原子;主要进攻2-乙烯基氧杂环丁烷乙烯基的β-位碳原子,发生S_N2'开环反应。只有在酸性条件下,亲核性相对较弱的含氧和卤素亲核试剂才受电子效应控制,主要进攻氧杂环丁烷位阻大的氧邻位碳原子。亲电性开环、自由基开环、路易斯酸催化的开环和钯催化的氢解开环都是在氧杂环丁烷位阻大的氧邻位碳原子一侧开环。希望本文的结论能够为利用氧杂环丁烷开环反应的同行提供一些有价值的信息,促进氧杂环丁烷开环反应的应用。

Ring-opening reactions of oxetanes include nucleophilic,electrophilic,radical,acid-catalyzed,and reductive ring-opening modes. Ring-opening reactions of unsymmetric oxetanes and their regioselectivity are summarized and reviewed. The regioselectivity of these ring-opening reactions is mainly influenced by steric and electronic effects. Nucleophilic ring-opening reactions of unsymmetric oxetanes with various nucleophiles are major ring opening reactions of oxetanes. Strong nucleophiles mainly attack the less substituted oxygen-adjacent carbon atom of unsymmetric oxetanes（ steric effect control）. They attack on the β-carbon atom of the vinyl group in 2-vinyloxetanes,undergoing an S_N2’ ring-opening reaction. Only in the presence of acids,unsymmetric oxetanes can be attacked on their more substituted oxygen-adjacent carbon atom with weak nucleophiles such as O-nucleophiles or halides（ electronic effect control）. However,electrophilic ring-enlargement reactions,radical ring-opening coupling reactions,Lew is acid-catalyzed ring-opening reactions and Pd-catalyzed hydrogenolysis reactions take place at sterically hindered oxygen-adjacent carbon atom of unsymmtric oxetanes. The current summarized results provide important and useful imformation for chemists who apply ring-opening reactions of oxetanes and promote the application of ring-opening reactions of oxetanes.