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

• Published in: European journal of organic chemistry 2021-06, Vol.2021 (22), p.3123-3132
• Main Authors: Ali, Hasrat, Guérin, Brigitte, Lier, Johan E.
• Format: Article
• Language: English
• Subjects: Absorption; Alkenes; Aromatic compounds; BODIPY; Chemical reactions; Cross coupling; Emission spectra; Fluorescence; NMR; Nuclear magnetic resonance; Palladium; Protonation; Sonogashira reaction; Stille reaction; Substitutes; UV/Vis; X-ray diffraction analysis
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202100133

4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives bearing gem‐dibromovinyl moieties at either the β‐ or α‐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 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. BODIPY derivatives bearing gem‐dibromovinyl moieties (α‐ or β‐positions of the pyrrole rings, directly or through phenyl spacers) undergo efficiently Sonogashira and Stille Pd‐catalyzed cross‐coupling resulting in the formation of 1,1‐diynyl‐1‐alkene and 1,1‐diphenyl‐1‐alkene products. A pronounced red shift of absorption maxima occurs when substituents are at the α‐position rather than the β‐position of the pyrrole ring. 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.