Metal‐Free Intermolecular Cfur–Nsucc Bond Coupling of Highly Substituted 3‐Furancarbaldehydes and Their Use in meso‐Substituted BODIPY Synthesis
Two novel highly substituted 3-furancarbaldehydes have been synthesized by the reaction of 3-furancarbaldehyde and NBS in chloroform and N,N-dimethylformamide. Importantly, NBS serves as a succinimide donor under mild metal-free conditions whereas NCS does not. Also, NBS does not undergo the same reaction with 3-thiophenecarbaldehyde. We show how solvent plays a crucial role in C–Br and C–N bond formation, including through the use of DFT calculations, which demonstrated that a bromonium-mediated transformation is energetically allowable. Other 3-furan derivatives gave no evidence of analogous C–N bond-forming reactions, underscoring the potential uniqueness of the 3-furancarbaldehyde moiety. A variety of meso-aryl- and -hydrogen-substituted BODIPY species were then prepared from pyrrole and 2,4-dimethylpyrrole and characterized by NMR spectroscopy and crystallography.