Pd-catalyzed dehydrogenative arylation of arylhydrazines to access non-symmetric azobenzenes, including tetra-ortho derivatives

TL;DR

This paper introduces a new method to efficiently create non-symmetric azobenzenes using a palladium-catalyzed reaction, solving previous challenges in their synthesis.

Contribution

A one-pot Pd-catalyzed dehydrogenative C–N coupling method for synthesizing non-symmetric azobenzenes, including tetra-ortho derivatives.

Findings

The method enables selective N-arylation at the terminal nitrogen using bulky phosphine ligands.

The protocol is robust, tolerating various functional groups and working under O2 and water conditions.

Tetra-ortho-substituted azobenzenes were successfully synthesized for the first time using this approach.

Abstract

Azobenzenes are photoresponsive compounds widely used in molecular switches, light-controlled materials, and sensors, but despite extensive studies on symmetric derivatives, efficient methods for synthesizing non-symmetric analogues remain scarce due to regioselectivity issues, multistep procedures, and limited applicability to tetra-ortho-substituted structures. Herein, we describe a direct, one-pot Pd-catalyzed dehydrogenative C–N coupling between aryl bromides and arylhydrazines to access non-symmetric azobenzenes. The use of bulky phosphine ligands and sterically tuned substrates promotes selective N-arylation at the terminal nitrogen. The protocol tolerates a wide range of functional groups and enables the synthesis of well-decorated azobenzenes, including tetra-ortho-substituted derivatives. Notably, the reaction proceeds under an O2 atmosphere and in the presence of water, highlighting its robustness.

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