Pd-Catalyzed Sonogashira Cross-Coupling Reactions of gem-Dibromovinyl BODIPY Derivatives

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives bearing gem-dibromovinyl moieties at either the beta- or alpha-positions of the pyrrole rings, directly or through phenyl spacers, undergo efficiently Sonogashira and Stille Pd-catalyzed cross-coupling. The structures of the resulting 1,1-diynyl-1-alkene and 1,1-diphenyl-1-alkene products were assigned using MS, NMR and in some cases X-ray diffraction analysis. 1,1-Diynyl-1-alkene BODIPYs exhibit red shifted absorption maxima, particularly when substituents were introduced at the alpha-position rather than the beta-position of the pyrrole ring. Aromatic compounds showed larger red shifts as compared to the aliphatic substituted analogs. The highest red shifts were observed with compounds featuring electron donating substituents. Spectroscopic properties of alpha-substituted 1,1-diynyl-p-N,N-dimethylaminophenyl-1-alkenes are sensitive to protonation resulting in remarkable pH-responsive changes in the absorption and fluorescence emission spectra.

Automated summary

This study reveals that the introduction of substituents at different positions of the pyrrole ring in BODIPY derivatives has a significant impact on their spectroscopic properties, with compounds featuring electron donating substituents showing larger red shifts. Additionally, some compounds exhibit remarkable pH-responsive changes in absorption and fluorescence emission spectra during protonation.