Sciencemadness Discussion Board

Preparation of trimethylsulfoxonium?

myr - 22-11-2018 at 11:17

Trimethylsulfoxonium is a rather useful reagent, allowing for the easy synthesis of epoxides and cyclopropanes with phase-transfer catalysts.

Example from 10.1002/anie.197308451:
Quote:

Benzaldehyde (10.6 g, 0.1 mol) and TBAI (0.5 g, 1.35 mol) are dissolved in dichloromethane (l00ml) and a layer of 50 '4 aqueous sodium hydroxide is introduced underneath this solution. Trimethylsulfonium iodide (20.4 g, 0.1 mol) is then added and the whole is warmed at 50 C with vigorous stirring for 48 h, whereupon the originally undissolved sulfonium salt disappears. The reaction mixture is next poured on ice, and the organic phase is separated, washed with water and dried. 92% yield


I wish to use this reaction to prepare a ring-substituted styrene oxide.

Is it possible to prepare it using methyl tosylate instead of MeI or MeBr? MeOTs is quite less toxic (although far from harmless) but still quite reactive. How about MeCl?

The standard procedure:
Quote:

A solution of dimethyl sulphoxide (48 g, 0.62 mmol) and methyl iodide (205 g, 1.45 mol) was refluxed under an argon atmosphere for 3 days. The solid produced was filtered, washed with chloroform (4 x 50 mL), recrystallised from water and dried in vacuo to yield the crystalline adduct (119 g, 87 %)

UC235 - 22-11-2018 at 20:00

Your first reference is using trimethylsulfonium, S(Me)3+ while the latter preparation is for trimethylsulfoxonium, O=S(Me)3+. The former can be produced in good yield by slowly adding bromine to DMSO, as detailed elsewhere on this forum, and is also a useful methylating agent for phenols.

myr - 23-11-2018 at 06:07

Quote: Originally posted by UC235  
Your first reference is using trimethylsulfonium, S(Me)3+ while the latter preparation is for trimethylsulfoxonium, O=S(Me)3+. The former can be produced in good yield by slowly adding bromine to DMSO, as detailed elsewhere on this forum, and is also a useful methylating agent for phenols.


Thanks for pointing that out. Both S(Me)3+ and O=S(Me)3+ respective methylides can be easily prepared under these conditions, but on rereading the paper, dimethylsulfoxonium methylide gives a low yield and side reactions with benzaldehyde.

A second question: how do I remove Me2S?

UC235 - 23-11-2018 at 16:54

Me2S boils at 35C. You get rid of it the same way you would get rid of very smelly ether. Bleach oxidizes it to odorless DMSO and dimethyl sulfone and is a good chemical scrubber.