Rh(III)-Catalyzed C–H Activation of Boronic Acid with Aryl Azide

Abstract

A Rh(III)-catalyzed C-H activation of boronic acid with aryl azide to obtain unsymmetric carbazoles, 1 H-indoles, or indolines has been developed. The reaction constructs dual distinct C-N bonds via sp/sp C-H activation and rhodium nitrene insertion. Synthetically, this approach represents an access to widely used carbazole derivatives. The practical application to CBP and unsymmetric TCTA derivatives has also been performed. Mechanistic experiments and DFT calculations demonstrate that a five-membered rhodacycle species is the key intermediate.

Recent Advances in the Synthesis of 5‐MemberedN‐Heterocycles via Rhodium Catalysed Cascade Reactions

“…Experimental studies and theoretical calculations revealed that CÀ H bond activation, nitrene formation, and the migratory insertion of a five-membered rhodacycle intermediate were the key steps (Scheme 42). [90] 3,4-Polyfused oxindole represents a core structural motif in numerous biologically important natural products such as welwetindolinone, [91a,b] xylanigripones, [91c] ergoline-8-amine, [91d] and communesins. [91e,f] Earlier reports suggested asymmetric Heck or Heck-type reaction has been successfully forged into C3-disubstituted or spirocyclic oxindoles.…”

“…Experimental studies and theoretical calculations revealed that C−H bond activation, nitrene formation, and the migratory insertion of a five‐membered rhodacycle intermediate were the key steps (Scheme 42). [90] …”

Organic Azides: Versatile Synthons in Transition Metal‐Catalyzed C(sp2)−H Amination/Annulation for N‐Heterocycle Synthesis

“…In 2018, Zhang and co‐workers applied this strategy to the efficient synthesis of unsymmetric carbazoles, 1 H ‐indoles and indolines from aryl boronic acids and aryl azides (Scheme 13). [20] The usage of biphenyl boronic acid mainly led to carbazoles. (2‐Vinylphenyl)‐boronic acids and (2‐( tert ‐butyl)phenyl)boronic acids yielded the corresponding indoles and indolines at an elevated temperature in toluene.…”

Recent Progress in the C−N Bond Formation via High‐Valent Group 9 Cp*M(III)‐Catalyzed Directed sp2 C−H Activation

“…Azine directed C-2 amidation was also demonstrated recently. [9e] The work by Zhang and co-workers [22] revealed that boronic acid, in particular, [1,1'-biphenyl]-2-ylboronic acid derivatives 56 can be aminated with aryl azides 57 to give various unsymmetrical carbazoles 58 (Scheme 17). The method has been applied to synthesize photoelectric material N,N'-dicarbazolyl- The activation of benzaldehydes, where aldehyde is used as a directing group, is challenging due to low Lewis basicity of the carbonyl group.…”