On the Redox Properties of the Dimers of Thiazol-2-ylidenes That Are Relevant for Radical Catalysis

We report the isolation and study of dimers stemming from popular thiazol-2-ylidene organocatalysts. The model featuring 2,6-di(isopropyl)phenyl (Dipp) N-substituents was found to be a stronger reducing agent (E-ox = -0.8 V vs SCE) than bis(thiazol-2-ylidenes) previously studied in the literature. In addition, a remarkable potential gap between the first and second oxidation of the dimer also allows for the isolation of the corresponding air-persistent radical cation. The latter is an unexpected efficient promoter of the radical transformation of alpha-bromoamides into oxindoles.

Automated summary

We isolated and studied dimers derived from popular thiazol-2-ylidene organocatalysts. The model compound with 2,6-di(isopropyl)phenyl (Dipp) N-substituents was found to be a stronger reducing agent compared to previously studied bis(thiazol-2-ylidenes). Furthermore, the significant potential difference between the first and second oxidation of the dimer allows for the isolation of an air-persistent radical cation, which efficiently promotes the radical transformation of alpha-bromoamides into oxindoles.