Atroposelective Synthesis of Azobenzenes by Palladium-Catalyzed Cross-Coupling of Racemic Biaryl Triflates and Diazenyl Pronucleophiles

A kinetic resolution of racemic biaryl monotriflates by an atroposelective palladium-catalyzed diazenylation enables the synthesis of azobenzene derivatives decorated with an axially chiral substituent. The C(sp2)-N(sp2) cross-coupling reaction makes use of silylated diazenes as diazenyl anion equivalents, and chiral ferrocene-based bisphosphine ligands act as effective supporting ligands. The resulting chiral azobenzenes bearing binaphthyl and naphthyl/phenyl backbones undergo reversible trans-cis isomerization under irradiation with LEDs of different wavelengths, highlighting their potential use in photoresponsive chiroptical materials.