Regioselective Synthesis of 5-Monostyryl and 2-Tetracyanobutadiene BODIPY Dyes

Several unsymmetrically 2,5-disubstituted BODIPY dyes were obtained from 2-substituted derivatives (iodo, ethynylaryl) using a regioselective Knoevenagel condensation reaction with dimethylaminobenzaldehyde. The unsaturated, unsymmetrical 2-ethynyl-5-styryl-BODIPY undergoes a regioselective [2 + 2] cycloaddition reaction with tetracyanoethylene leading to the 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) derivative. This shows rich redox activity with two reversible oxidation and three reversible reduction waves at +0.72 V, +1.04 V; −0.32 V, −0.78 V, and −1.50 V, respectively.