Methyl-to-double bond transfer in the gas phase: A theoretical study

A novel methyl-to-double bond transfer between the methylsulfonium ion and alkene has been given a systematic theoretical study with density functional theory (DFT) method. Two possible pathways have been proposed: (i) methyl attack on the terminal carbon of the double bond and (ii) formation of the bridged methyl-onium ion. The concrete pathway is mainly associated with the type of the alkene rather than that of the methyl donor. The symmetrical aliphatic alkene favors pathway ii, while aromatic alkene and asymmetrical aliphatic one favor pathway i. In pathway i, the methylation site is affected by the substituent. Moreover, for the S-substituted methylsulfonium ion, the electron-withdrawing group can promote the methyl transfer, while the electron-donating group has the opposite effect.