Oxidative Approach Enables Efficient Access to Cyclic Azobenzenes

Azobenzenes are versatile photoswitches
that have found widespread
use in a variety of fields, ranging from photopharmacology to the
material sciences. In addition to regular azobenzenes, the cyclic
diazocines have recently emerged. Although diazocines have fascinating
conformational and photophysical properties, their use has been limited
by their synthetic accessibility. Herein, we present a general, high-yielding
protocol that relies on the oxidative cyclization of dianilines. In
combination with a modular substrate synthesis, it allows for rapid
access to diversely functionalized diazocines on gram scales. Our
work systematically explores substituent effects on the photoisomerization
and thermal relaxation of diazocines. It will enable their incorporation
into a wide variety of functional molecules, unlocking the full potential
of these emerging photoswitches. The method can be applied to the
synthesis of a new cyclic azobenzene with a nine-membered central
ring and distinct properties.