Transition Metal‐free C−H Sulfonylation and Pyrazole Annulation Cascade for the Synthesis of 4‐Sulfonyl Pyrazoles

Abstract

A practical protocol for the synthesis of 4-sulfonyl pyrazoles via the reactions of readily available N,N-dimethyl enaminones and sulfonyl hydrazines has been developed via the catalysis of molecular iodine in the presence of TBHP and NaHCO 3 at room temperature. The pyrazole products have been constructed via the tandem C(sp 2 )À H sulfonylation and a pyrazole annulation without employing any transition metal catalyst or reagent, thus providing a practical new method for the synthesis of the novel pyrazoles bearing a sulfonyl side chain in the heterocycle.

Recent Advances in Organic Synthesis Based on N,N-Dimethyl Enaminones

“…Recently, our group and Wan's group independently reported a facile approach for the synthesis of N-sulfonyl pyrazoles from readily available sulfonyl hydrazines and N,Ndimethyl enaminones under p-TSA-promoted and I 2 -catalyzed conditions, respectively (Scheme 31). 33,34 In our work, condensation of the carbonyl group of the N,N-dimethyl…”

Recent advances in transition metal-free annulation toward heterocycle diversity based on the C–N bond cleavage of enaminone platform

“…In 2020, N , N -disubstituted enaminones were successfully used in an I 2 /TBHP catalytic system as the starting material by using DCM as solvent for the synthesis of the corresponding pyrazoles (Scheme 28). 58 The reaction process was almost the same as the above radical protocol. Many 4-tosyl-5-phenyl pyrazoles have been prepared by this transition metal-free protocol under mild conditions with good yields.…”

Recent Advances in Reactions Using Enaminone in Water or Aqueous Medium

“…Notably, such method for the synthesis of sulfonyl side chain functionalized pyrazoles in water could only be efficient when NH 2 ‐enaminones was used. The reactions of N,N ‐disubstituted enaminone with sulfonyl hydrazines need to be run in organic medium to provide corresponding pyrazoles with satisfactory result, [24] demonstrating the important role of the NH 2 group in enaminones by forming hydrogen bonds with water to facilitate the reactions.…”