Regioselective Construction of Hexa‐Substituted Alkynyl Benzenes via Ni(0)‐Catalyzed [2+2+2] Cyclotrimerization: Mechanistic and Spectroscopic Insights

We report a regioselective Ni(0)‐catalyzed [2 + 2 + 2] cyclotrimerization of 1,3‐diynes to provide alkynyl hexa‐substituted benzenes (HSBs). The methodology demonstrates a broad scope, accommodating both symmetrical and unsymmetrical 1,3‐diynes bearing a wide array of functional groups and yielding the corresponding HSBs. With glycosyl‐appended 1,3‐diynes as substrates, multivalent glycosystems of varying degrees were achieved. These multivalent glycosystems could act as substrates for lectin‐binding and serve as vehicles for drug delivery. Control experiments and kinetics analysis were conducted to gain mechanistic insights. A detailed density functional theory (DFT) analysis of the plausible mechanism provided insights into the origin of the regioselectivity. The HSB products with extended conjugation displayed intriguing photophysical characteristics, and their absorption and emission properties were investigated. The redox behavior of the tri‐ and hexa‐ferrocenyl HSBs was studied by voltammetry (CV, DPV) and EPR.