[1468-37-7] · C4H6O2S4 · Dimethyl Dithiobis(thioformate) · (MW 214.38)
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, R
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.
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.
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
Kyoto Institute of Technology, Japan
Kyoto University, Japan