Theoretical studies on intramolecular methyl transfer in the S-2-alkenyl-dimethylsulfonium ion

► Using DFT to study the intramolecular methyl transfer in S-2-alkenyl-dimethylsulfonium ion. ► The substituent on the olefinic bond is sensitive to the methyl transfer pathway. ► The advantageous transition state always exhibits methyl retention-chair mode.