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.

Recent developments in thiochromene chemistry

“…In 2023, Deepika et al reported a novel de-nitrative C–S coupling methodology for synthesizing pyrazole-tethered thiochromenes ( 89 ) using elemental sulfur ( 88 ) as the sulfur source. 48 This environmentally benign protocol leveraged 1,4-diazabicyclo-[2.2.2]-octane (DABCO) for activating the sulfur source and aided in regioselective C–H bond formation, simultaneously removing the nitro motif from the arene ring. Following control experiments, two possible mechanistic pathways were identified for this reaction.…”