Direct and Versatile Synthesis of Red‐Shifted Azobenzenes

Abstract

A straightforward synthesis of azobenzenes with bathochromically‐shifted absorption bands is presented. It employs an ortho‐lithiation of aromatic substrates, followed by a coupling reaction with aryldiazonium salts. The products are obtained with good to excellent yields after simple purification. Moreover, with the presented methodology, a structurally diverse panel of different azobenzenes, including unsymmetric tetra‐ortho‐substituted ones, can be readily obtained, which paves the way for future development of red‐light‐addressable azobenzene derivatives for in vivo application.Red‐shifted tetra‐ortho‐substituted azobenzenes were synthesized in a rapid manner with high functional group tolerance (see picture). The privileged tetra‐ortho‐methoxy, ‐chloro, and ‐fluoro azobenzenes become readily accessible, which paves the way for future applications of red‐shifted azobenzenes in material and biological sciences.