in lower yields. Thermalringopening of 1-(methylthio)cyclopropenes took place readily at room temperature or on heating at around 80 °C to give indene and/or butadiene derivatives in good yields. Product analysis of the reaction in methanol as well as kinetic studies of one of 1-(methylthio)cyclopropenes gave strong evidence for the intermediacy of vinylcarbene in the ringopening of cyclopropene