1,2-Azaborines represent a unique class of benzene isosteres that holds great potential for various applications. However, it remains a long-standing challenge to prepare monocyclic 1,2-azaborines in an efficient and modular manner. Here we report a straightforward method to directly access diverse multi-substituted 1,2-azaborines from readily available cyclopropyl imines/ketones and dibromoboranes under relatively mild conditions. The reaction is scalable, shows a broad substrate scope, and tolerates a range of functional groups. The utility of this method is demonstrated in the concise syntheses of BN isosteres of a PD-1/PD-L1 inhibitor and pyrethroid insecticide bifenthrin. Combined experimental and computational mechanistic studies suggest that the reaction pathway involves boron-mediated cyclopropane ring-opening and base-mediated elimination, followed by an unusual low-barrier 6π-electrocyclization accelerated by the BN/CC isomerism.

中文翻译：

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1,2-azaborines 通过开环 BN-isostere 苯并环化的模块化合成

1,2-Azaborines 代表了一类独特的苯电子等排体，在各种应用中具有巨大的潜力。然而，以高效和模块化的方式制备单环 1,2-azaborines 仍然是一个长期存在的挑战。在这里，我们报告了一种直接的方法，可以在相对温和的条件下从现成的环丙基亚胺/酮和二溴硼烷中直接获得多种多取代的 1,2-azaborines。该反应是可扩展的，显示出广泛的底物范围，并且可以容忍一系列的官能团。这种方法的实用性在 PD-1/PD-L1 抑制剂和拟除虫菊酯杀虫剂联苯菊酯的 BN 等排体的简明合成中得到了证明。结合实验和计算机理研究表明，反应途径涉及硼介导的环丙烷开环和碱基介导的消除，