Abstract: Vinylglyoxal derivatives of the general formula I ##STR1## where R is straight-chain or branched alkyl or alkenyl, cycloalkyl or unsubstituted or substituted phenyl, are prepared by a process in which bicyclo[2.2.1]hept-5-enecarbaldehyde of the formula V ##STR2## is either (a) subjected to autocondensation with formation of a compound of the formula VII ##STR3## or (b) reacted with a compound of the general formula IIR-CH.dbd.O (II)where R has the above meanings, with formation of a mixture of the compounds of the general formulae VIII (a) and (b) ##STR4## where R is as defined above, in the presence of a catalyst, and the compound of the formula VII or the compounds of the formulae VIII (a) and (b) is or are oxidized to the corresponding dicarbonyl compounds, after which gas-phase pyrolysis is carried out at from 500.degree. to 700.degree. C. and under reduced pressure, in particular less than 10.sup.-1 mbar, and, if desired, the resulting compound of the general formula I is further purified.