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

Abstract

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives bearing gem-dibromovinyl moieties at either the βor αpositions 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-1alkene 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 α-position rather than the β-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 α-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.