1304031-27-3Relevant academic research and scientific papers
Concerning the deprotonation of the trimethylsulfonium ion by the dimethylsulfinyl anion
Haiss, Peter,Zeller, Klaus-Peter
experimental part, p. 7748 - 7754 (2011/12/03)
As shown by deuterium labelling experiments, the deprotonation of the trimethylsulfonium ion (1) by the dimsyl anion (8) is accompanied by extensive hydrogen exchange. This cannot be explained by an acid-base equilibrium between the trimethylsulfonium ion (1) and the dimsyl anion (8) on one side and dimethylsulfonium methylide (2) and DMSO on the other side, because for thermodynamic reasons this process is irreversible due to the limited life-time of 2. Therefore, the isotopic exchange that accompanies the deprotonation is an indicator of a more complex deprotonation process. It is suggested that in a kinetically controlled reaction, a proton of 1 is transferred to the O-atom of 8 rather than to the carbanionic centre. This means that instead of DMSO, its tautomer, hydroxy-methylsulfonium methylide (10), is obtained in the deprotonation process. Similarly, in the acid-base interaction between DMSO and its conjugate base 8, the formation of the DMSO tautomer 10 is kinetically favoured. The intermediate 10 produced in this way transfers a DMSO-derived proton to 1 when it intervenes in the back reaction 10 + 2 → 8 + 1. An alternative mechanism based on methyl group exchange between 1 and 8 could be excluded by a 13C-labelling experiment. The hydrogen exchange according to the suggested scenario is taking place in competition with the reaction of dimethylsulfonium methylide (2) with electrophilic substrates. This explains the different degrees of isotopic exchange when compounds of different electrophilicities are used to scavenge 2 from the deprotonation-hydrogen distribution equilibria.
The mechanism of the ortho-methylation of nitrobenzenes by dimethylsulfonium methylide
Haiss, Peter,Zeller, Klaus-Peter
experimental part, p. 295 - 301 (2011/02/28)
Nitrobenzenes carrying an ortho substituent are selectively methylated at the free ortho position by reaction with dimethylsulfonium methylide. The importance of the ortho substituent is demonstrated by the failure of the methylation of nitrobenzene and 3- and 4-nitroanisole. This is explained by the out-of-plane geometry of the nitro group in the ortho-substituted derivative, which enables a specific interaction between the ylide and the nitro group favourable for attack of the methylide C atom at the neighbouring free ortho position. As shown by appropriate deuterium-labelling studies, the addition is followed by an E1-like β-elimination with displacement of dimethyl sulfide and subsequent protonation of the elimination product. The nucleophilic ortho-methylation of 2-nitroanisole by dimethylsulfonium methylide is explained by a reaction sequence including intermediates A to D. Copyright
