DMSO (dimethyl sulfoxide) as a two-methyl source: C-H (trideutero)methylation of (iso)quinolines and their N-oxides

Abstract

(Trideutero)methylation is an important process in both chemistry and biology. In this context, DMSO(-d6) has largely been used as •CH3/•CD3 source. Typically, all known DMSO(-d6)-based (trideutero)methylation procedures: i) employ a significant excess of DMSO(-d6) as a reagent and solvent, and ii) detach just one of the two (trideutero)methyl groups of DMSO(-d6). For the first time, using persulfate (S2O82-) and graphitic carbon nitride (g-C3N4) visible-light photocatalysis, we herein describe a methodology that works with merely stoichiometric quantity of DMSO(-d6) and draws and employs both of the DMSO(-d6)'s (trideutero)methyl groups for C-H (trideutero)methylation of heteroarenes and their N-oxides. We also described the reusability of g-C3N4 catalyst and a plausible reaction mechanism. The usage of DMSO(-d6) requires careful financial management due to its fairly high retail price (around 600 USD for 100 mL). We thus feel that the method for (trideutero)methylation described here, which uses merely stoichiometric amounts of DMSO(-d6), is far less expensive and environmentally benign than the methods described in the literature.