A General and Practical Synthesis of Chiral 1, 2‐Oxazetidines. Issue 2 (22nd January 2020) - Yang, Jinggang
Abstract: 1, 2‐Oxazetidines are valuable small strained molecules that could be used to create new and conventionally difficult‐to‐access chemical transformations. Currently, asymmetric methods towards this class of heterocycles are very rare. Herein, we report a general and practical method to access a series of structurally diverse chiral 1, 2‐oxazetidines from readily available chiral epoxides and α‐bromo esters in 3–4 steps by using mild Mitsunobu reactions as an efficient ring‐closure approach to form the highly strained four‐membered rings. The new method is operationally simple, and a range of N ‐nosyl‐protected 3‐ and 4‐substituted as well as 3, 4‐disubstituted chiral 1, 2‐oxazetidines could be conveniently prepared in gram‐scale with excellent enantioselectivities (93–99% ee ) and good overall yields for the first time. Abstract : Synthetic methods : A general and practical approach to access structurally diverse chiral 1, 2‐oxazetidines, a class of synthetically valuable but rarely investigated small strained synthons, has been realized for the first time. The new method allows to prepare the target compounds in 3–4 steps with excellent enantioselectivities and good overall yields on gram scale.