Oxidative C-H/C-H Cross-Coupling of [1,2,4]Triazolo[1,5- a]pyrimidines with Indoles and Pyrroles: Discovering Excited-State Intramolecular Proton Transfer (ESIPT) Fluorophores.

A highly efficient Rh(III)-catalyzed oxidative C-H/C-H cross-coupling of [1,2,4]triazolo[1,5- a]pyrimidines (TAP) with indoles and pyrroles has been developed, which provides an opportunity to rapidly assemble a large library of novel excited-state intramolecular proton transfer (ESIPT) fluorophores. The resulting 7-(pyrrol-2-yl)TAPs only show the enol-form emission, while 7-(indol-2-yl)TAPs would undergo an ESIPT process and mainly exhibit the keto-form emission. In highly polar solvents, the enol-form emission of 7-(indol-2-yl)TAPs is enhanced significantly, thus showing the dual emission of enol and keto forms.