Dimerization of 3-Chlorooxindoles Mediated by Potassium Ethylxanthate: Synthesis of Isoindigos

A novel dimerization of 3-chlorooxindoles promoted by potassium ethylxanthate to access isoindigo derivatives is described. The reactions proceeded readily at room temperature in short reaction times. A mechanistic study revealed that the 3-chlorooxindole is initially converted into O-ethyl S-(2-oxo-2,3-dihydro-1H-indol-3-yl) dithiocarbonate, which subsequently undergoes dimerization with elimination of carbon disulfide. In almost all cases, analytically pure isoindigos were isolated in moderate to good yields without a requirement for chromatographic purification.

Automated summary

A novel dimerization of 3-chlorooxindoles promoted by potassium ethylxanthate was described to access isoindigo derivatives, with the reactions proceeding readily at room temperature in short reaction times. Mechanistic studies revealed the conversion of 3-chlorooxindole into O-ethyl S-(2-oxo-2,3-dihydro-1H-indol-3-yl) dithiocarbonate, followed by dimerization with the elimination of carbon disulfide to yield analytically pure isoindigos in moderate to good yields, without the need for chromatographic purification.