Fusion of Photochromic Reaction and Synthetic Reaction: Photoassisted Cyclization to Highly Strained Chiral Azobenzenophanes

A method for synthesizing highly strained cyclic structures by combining photochromic and synthetic reactions is described. Tightly linked azobenzene–binaphthyl dyads (R)-4 and (R)-6 could not be obtained by conventional cyclization, but continuous application of photoirradiation, which induced (E)→(Z) isomerization of the azobenzene moiety, allowed the cyclization reaction to proceed, affording the desired chiral azobenzenophanes.