The asymmetric transfer hydrogenation of 3‐substituted 2H‐1,4‐benzoxazines with an azeotropic mixture of HCO2H/NEt3 (5/2) using tethered Cp*Rh(III)‐diamine catalysis has been realized. This process allows access to a broad range of chiral 3,4‐dihydro‐2H‐1,4‐benzoxazines in high yields with up to 99% ee, and tolerates a variety of functional groups. The enantiocontrol is achieved by the judicious choice of catalyst and hydrogen source. This reaction proceeds with unexpected reversal of enantioselectivity, which is attributed to the acidic reaction conditions and the hydrogen bond between the N−H of the rhodium species and the O atom in the substrate.

中文翻译：

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在栓系 Cp*Rh（III）-二胺催化下 3-取代 2H-1,4-苯并恶嗪的不对称转移氢化与对映选择性的意外逆转


使用栓系 Cp*Rh（III）-二胺催化，实现了 3-取代的 2H-1,4-苯并恶嗪与 HCO2H/NEt3 （5/2） 共沸混合物的不对称转移氢化。该工艺允许以高达 99% 的 ee 获得广泛的手性 3,4-二氢-2H-1,4-苯并恶嗪，并耐受多种官能团。对映体控制是通过明智地选择催化剂和氢源来实现的。该反应以对映选择性的意外逆转进行，这归因于酸性反应条件以及铑物质的 N-H 与底物中 O 原子之间的氢键。