Regioselective Halogenation of BOPPY Fluorophores and Subsequent Diversification via Cross-Coupling and Aromatic Nucleophilic Substitution Strategies

The regioselective mono- and tribromination of a BOPPY dye followed by its reactivity under Pd-catalyzed cross-coupling and nucleophilic substitution reactions are reported. The brominated BOPPYs undergo Pd(0)-catalyzed cross-couplings with a variety of boronic acids and organotin reagents to give the corresponding products in good-to-excellent yields. Nucleophilic aromatic substitutions occur both on the mono- and tribromo-BOPPYs. The reactivity order of the latter is C3-Br > C1-Br > C2-Br, while in the cross-coupling reactions using Pd(PPh3)4, it is C1-Br > C3-Br > C2-Br, likely due to steric interaction upon Pd(PPh3)2 insertion into the C3-Br bond and the slightly longer and weaker C1-Br bond. The functionalized BOPPY derivatives showed pronounced bathochromic shifts in their absorption and emission bands compared with the starting compound, and fluorescence quantum yields depend on the nature and position of the substituent.