SH-Methylation of SH-Containing Heterocycles with Dimethyl Carbonate via Phase-Transfer Catalytic Reaction

Abstract

A reaction of SH-containing heterocycles with dimethyl carbonate (DMC) in the presence of K₂CO₃ and tetrabutylammonium bromide (Bu₄NBr) gave heteroaryl methyl thioethers in 44–93% yields. The reaction was carried out under mild conditions. This method provided a useful synthetic method for preparation of various heteroaryl methyl thioethers without the use of toxic methylic halides or dimethyl sulfate.

Keywords:

• Dimethyl carbonate
• methylation
• phase-transfer catalyst
• SH-containing heterocycle
• thioether

ACKNOWLEDGMENTS

This work was supported by the National Natural Science Foundation of China (50773009) and by the Program for Changjiang Scholars and Innovative Research Team in University (IRT0526).

Notes

^a Reaction conditions: 2-mercaptobenzothiazole = 10 mmol, DMC = 180 mmol, temperature = 90 °C.

^b Ammonium quaternary salt = 2 mmol.

^c Base = 15 mmol.

^d Isolated yields based on 2-mercaptobenzothiazole after column chromatography.

^e Temperature = 70 °C.

^a Reaction conditions: substrates = 10 mmol, DMC = 180 mmol, Bu₄NBr = 2 mmol, base = 15 mmol, temperature = 90 °C.

^b Isolated yields after column chromatography.