Flash vacuum pyrolysis (FVP) of dimethyl E-or Z-pyrrol-2-ylbut-2-enedioate 5 at 700° C gave 1-methoxycarbonylpyrrolizin-3-one 1. The sequence involves E-to Z-isomerisation (if necessary), elimination of methanol and cyclisation; the elimination step is rate determining. The pyrrolizinone 1 is stable at low temperatures, but at room temperature dimerises spontaneously across the 1, 2-bond to give a mixture of trans-and cis-cyclobutanes 2 and ...
