Rh(III)-Catalyzed [4 + 1]-Annulation of Azoxy Compounds with Alkynes: A Regioselective Approach to 2H‑Indazoles

A rhodium-catalyzed regioselective C–H activation/cyclization of azoxy compounds with alkynes has been disclosed to construct a variety of 2H-indazoles. A [4 + 1]-cycloaddition rather than a normal [4 + 2] mode is observed in the process of cyclative capture along with an oxygen-atom transfer and a CC triple bond cleavage. This protocol features a broad substrate scope, a good functional group tolerance, and an exclusive regioselectivity.本研究报道了一种铑催化（rhodium-catalyzed）的区域选择性C–H活化（regioselective C–H activation）/环化反应，以氧化偶氮化合物（azoxy compounds）与炔烃（alkynes）为底物，构建多种2H-吲唑（2H-indazoles）类化合物。在环化捕获过程中，该反应采取[4+1]环加成（[4 + 1]-cycloaddition）而非常规的[4+2]环加成（[4 + 2]）模式，同时伴随氧原子转移（oxygen-atom transfer）与碳碳三键（CC triple bond）断裂。该合成方案具有底物适用范围广、官能团耐受性（functional group tolerance）良好以及区域选择性（regioselectivity）专一的特点。