Iron-Catalyzed Direct Sulfenylation and Selenylations of Phenylpyrazoles: Synthesis of Fipronil Derivatives with Disulfides Promoted by a Catalytic Amount of Iodine

Abstract

The direct thiolation of phenylpyrazole with disulfide using the FeBr₃/I₂ complex as the catalyst in MeCN at 80 °C was reported. With the optimum conditions, several fipronil derivatives of 4-sulfenylpyrazole were synthesized by the reaction of 5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl-lH-pyrazole-3-arbonitrile (1a) with disulfides (2) in moderate to good yields. The coupling reaction with diaryl diselane also occurred under similar conditions.

GRAPHICAL ABSTRACT

Keywords:

• Direct thiolation
• FeBr₃/I₂-catalyzed system
• fipronil derivatives
• selenylpyrazole
• sulfenylpyrazole

ACKNOWLEDGMENTS

The authors thank the National Natural Science Foundation of China (No. 20972114) and Zhejiang Provincial Natural Science Foundation of China (Y4100578).

Notes

^a Reaction conditions: 1a (0.4 mmol), 2a (0.2 mmol), Fe (10 mol%), and I₂ (10 mol%) in solvent (3 mL) at 80 °C for 42 h.

^b Isolated yield.

^c The structure .

^d The structure .

^e Without I₂.

^f I₂ (100 mol%).

^g At 100 °C.

^h At room temperature.

ⁱ Under N_2..

^a Reaction conditions: 1 (0.4 mmol), 2 (0.2 mmol), FeBr₃ (10 mol%), and I₂ (10 mol%) in MeCN (3 mL) at 80 °C for 42 h.

^b Isolated yield.

^a Reaction conditions: 1 (0.4 mmol), 2i and j (0.2 mmol), FeBr₃ (10 mol%), and I₂ (10 mol%) in MeCN (3 mL) at 80 °C for 42 h.