Domino C-H Sulfonylation and Pyrazole Annulation for Fully Substituted Pyrazole Synthesis in Water Using Hydrophilic Enaminones

The cascade reactions between NH2-functionalized enaminones and sulfonyl hydrazines have been developed for the synthesis of fully substituted pyrazoles. By making use of the hydrophilic primary amino group in the enaminones, the reactions proceed well in the medium of pure water in the presence of molecular iodine, TBHP, and NaHCO3 via cascade C-H sulfonylation and pyrazole annulation. The cleavage of the C-N bond in enaminones is confirmed by the experiment using N-15-labeled enaminone.