DMSO as a C<sub>1</sub> Source for [2 + 2 + 1] Pyrazole\nRing Construction via Metal-Free Annulation with Enaminones and Hydrazines

A cascade\nreaction between enaminones, hydrazines, and dimethyl\nsulfoxide (DMSO) for the synthesis of 1,4-disubstituted pyrazoles\ncatalyzed by molecular iodine in the presence of Selectfluor has been\nrealized. DMSO plays a dual role as the C₁ source and the\nreaction medium. In addition, the synthesis of 1,3,4-trisubstituted\npyrazoles using aldehydes as alternative C₁ building blocks\nhas also been achieved.