[222625-77-6] · C10H20N2OS2 · (248.41)
(reagent used as bis(propylthio)carbene precursor)
Physical Data: solid at -78°C, thermolysis occurs at 0°C and above.
Solubility: hexanes, cyclohexane, dichloromethane, benzene, toluene, xylene.
Form Supplied in: colorless oil as synthesized.
Purification: column chromatography at 0°C using hexanes-ethyl acetate (20:1); product elutes first; collect fractions in an ice bath; remove solvent in vacuo at 0°C; dry under high vacuum at 0°C for 1 h.
Handling, Storage, and Precautions: to prevent premature thermolysis, reagent should be stored in a sealed flask in a cooler with dry ice at -78°C. Since the reagent is thermally labile and thermolysis is exothermic, avoid exposure to heat to prevent rapid evolution of nitrogen gas leading to a possible explosion. Thermolysis will occur at 0°C and above. Use of an explosion shield and slow addition to refluxing solvents are recommended.
Upon thermolysis in refluxing benzene, 2,5-dihydro-2,2-dimethyl-5,5-bis(propylthio)-1,3,4-oxadiazole yields the bis(propylthio)carbene precursor, which reacts as a 1,1-dipole equivalent in [1+4] cycloaddition reactions with various vinyl isocyanate substrates leading to highly functionalized adducts such as hydroindolones (
Dimethoxy carbene has been shown to behave as a carbonyl 1,1-dipole equivalent in [1+4] cycloadditions with vinyl isocyanates also yielding functionalized adducts.6 However, the oxadiazole precursor requires higher thermolysis temperatures and hydrolysis of the acetals in the resultant adducts can be difficult for acid-sensitive systems.
When a large excess of 2,5-dihydro-2,2-dimethyl-5,5-bis(propylthio)-1,3,4-oxadiazole carbene precursor is added rapidly in refluxing benzene to a vinyl isocyanate, two equivalents of carbene add to the substrate prior to ring closure, leading to a six-membered adduct (
Addition of 2,5-dihydro-2,2-dimethyl-5,5-bis(propylthio)-1,3,4-oxadiazole in refluxing benzene and an aryl isocyanate releases the bis(propylthio)carbene in situ which then adds easily to the aryl isocyanate to yield a substituted isatin with the ketone functionality protected as a thioacetal (
Upon thermolysis of 2,5-dihydro-2,2-dimethyl-5,5-bis(propylthio)-1,3,4-oxadiazole in refluxing benzene and in the absence of any electrophile, the resultant bis(propylthio)carbene will dimerize (
Wayne State University, Detroit, MI, USA