2,5-Dithiacyclopentylideneketene and Ethenedithione, S=C=C=S, Generated by Flash Vacuum Pyrolysis

2,5-Dithiacyclopentylideneketene (4) is obtained by flash vacuum pyrolysis (FVP) of the Meldrum's acid derivative 1 and characterized by MS, IR, and NMR spectroscopy. 4 is stable in solution at -50-degrees-C. FVP of 4 as well as the isoxazolone derivatives 2 and 3 results in efficient cleavage into ethylene and ethenedithione, S=C=C=S, which is remarkably stable in the gas phase at high temperature, low pressure, and short contact times but extremely unstable in the condensed state or at higher pressures