DABCO Mediated Sulfur Activation-Intramolecular De-Nitration Strategy for the Synthesis of Novel Dihydrothiochromeno[4,3-c]pyrazoles

Abstract

A facile and highly efficient metal-free approach has been unfolded for the synthesis of novel dihydrothiochromeno[4,3-c]pyrazoles using elemental sulfur as a powerful sulfurating reagent. This method includes sp2 C−H functionalization followed by sp2 C−NO2 group displacement using elemental sulfur as an odourless sulfur source activated by DABCO in DMSO. Using the developed synthetic strategy, a library of 29 novel dihydrothiochromeno[4,3-c]pyrazoles, incorporating two pharmacologically important scaffolds has been synthesized in 52–76% yield with a broad substrate scope. A sensible mechanistic proposal has been projected based on control experiments.