A green and efficient iodine-catalyzed cross-dehydrogenative C–S coupling method for the synthesis of C-4 sulfenylated pyrazoles has been initially developed under metal-free conditions.

Peroxynitrite (ONOO−) is one of the important reactive oxygen species, which plays a vital role in the physiological process of intracellular redox balance. Revealing the biological functions of ONOO− will contribute to further understanding of the oxidative process of organisms. In this work, we designed and synthesized a novel red‐emitting fluorescent probe MCSA for the detection of ONOO−, which could rapidly respond to ONOO− within 250 s and exhibited high sensitivity to ONOO− with a low detection limit of 78 nM. Co‐localization experiments demonstrated MCSA had the ability to localize into the mitochondria and endoplasmic reticulum. What's more, MCSA enabled monitoring ONOO− level changes during tunicamycin‐induced endoplasmic reticulum stress. We have also successfully achieved the visual detection of exogenous and endogenous ONOO− in living cells and zebrafish. This work presented a chemical tool for imaging ONOO− in vitro and in vivo.

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