Dimethyl Dithiobis(thioformate)1

[1468-37-7]  · C4H6O2S4  · Dimethyl Dithiobis(thioformate)  · (MW 214.38)

(oxidizing reagent for conversion of thiols to disulfides;2 electrophilic sulfurization reagent3)

Physical Data: mp 23-23.5 °C; bp 90-94 °C/0.1 mmHg.

Solubility: readily sol common organic solvents.

Form Supplied in: colorless crystals or yellow oil.

Analysis of Reagent Purity: 1H NMR: d 4.30 (6H, s, OCH3); TLC, Rf 0.3 (silica gel, hexane).

Preparative Method: 1,2 oxidation of potassium O-methyl dithiocarbonate (prepared from potassium methoxide and carbon disulfide) with Nitric Acid or Chloramine-T.

Purification: recrystallization from ethanol.

Handling, Storage, and Precautions: decomposes at temperatures over 140 °C to yield O,S-dimethyl dithiocarbonate;1 stable for several months storage at rt. Handle in a fume hood.

Oxidation of Thiols to Disulfides.2

Most thiols are readily oxidized with this reagent in the presence of Pyridine as a catalyst to give the corresponding disulfides in excellent yields (eqs 1 and 2) (Table 1). In particular, this reagent is a clean and highly chemoselective oxidant for the conversion of thiols to disulfides without overoxidation to thiosulfinates, sulfinic acids, etc. The reactions are complete in a few minutes at rt. After evaporation of methanol and carbon disulfide (byproducts, eq 3) and pyridine (catalyst), most disulfides can readily be purified by recrystallization from the reaction mixture without chromatography.

Stereoselective a-Alkylidenation of g-Butyrolactone.3

In the presence of 2 equiv of Lithium Diisopropylamide, treatment of g-Butyrolactone with this reagent and aldehydes in THF at -78 °C produces a-alkylidene-g-butyrolactones (eq 4) (Table 2), the (E)-isomer being produced with high stereoselectivity. As shown in eq 5, the reaction proceeds via sulfurization of the lactone enolate, aldol condensation with the aldehyde, and final desulfurization of a thiirane.4,5 When a metal halide such as Zinc Chloride or Copper(I) Iodide is added to the reaction mixture, the (Z)-isomer becomes the predominant product. The excellent stereoselectivity observed in this reaction has been attributed to repulsion between the b-methylene of the lactone and the aldehyde substitutent in the transition state for aldol addition, the transition state being different in the presence or absence of an added metal halide (eqs 6-9). This procedure has advantages for the stereoselective preparation of either the (E)- or (Z)-isomer of 2-alkylidene carbonyl compounds.

1. Bulmer, G.; Mann, F. G. JCS 1945, 674.
2. Stout, E. I.; Shasha, B. S.; Doane, W. M. JOC 1974, 39, 562.
3. Tanaka, K.; Tamura, N.; Kaji, A. CL 1980, 595.
4. (a) Matsui, S. BCJ 1984, 57, 426. (b) Matsui, S.; Tanaka, K.; Kaji, A. S 1983, 127.
5. (a) Tanaka, K.; Uneme, H.; Yamagishi, N.; Tanikaga, R.; Kaji, A.; BCJ 1980, 53, 2910. (b) Tanaka, K.; Yamagishi, N.; Tanikaga, R.; Kaji, A. BCJ 1979, 52, 3619. (c) Tanaka, K.; Uneme, H.; Yamagishi, N.; Ono, N.; Kaji, A. CL 1978, 653. (d) Tanaka, K.; Yamagishi, N.; Uneme, H.; Tanikaga, R.; Kaji, A. CL 1978, 197.

Tatsuo Oida

Kyoto Institute of Technology, Japan

Sakae Uemura

Kyoto University, Japan

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