Fluorophores for Excited-State Intramolecular Proton Transfer by an Yttrium Triflate Catalyzed Reaction of Isocyanides with Thiocarboxylic Acids

Discovery of new chemical reactivity of a given functional group can often result in innovative synthesis of important chemical entities that possess unprecedented properties. We designed and developed a one-step synthesis of 5-amino-4-carboxamidothiazoles 1 by an yttrium-triflate-catalyzed reaction of thiocarboxylic acids 2 with isocyanides 3. In this reaction, both reactants 2 and 3 deviated from their normal reactivities because of metal coordination. The resulting heterocycles are novel prototypical structures for the double ESIPT process. Some of them were excited by visible light irradiation and emitted fluorescence at the NIR region with large Stokes shift, high quantum yield, and strong solvato-chromism.