The present invention relates to a process for preparing heterocyclic ketones of the formulae (I) and (la), by reacting a heterocyclic compound of the formula (II), with an α,β-unsaturated carboxylic acid of the formula (III), or with its anhydride of the formula (IV), where R1 is hydrogen or a C1-C40 carbon-containing group, R2 is hydrogen or a C1-C40 carbon-containing group, or R1 and R2 together form a cyclic ring system, R3 is a C1-C40 carbon-containing group and X is an element of the 16th group of the Periodic Table or is a divalent nitrogen group —(N—R4)—, where R4 is an electron-withdrawing radical which is selected from the group consisting of perhalogenated C1-C40 carbon-containing radicals and C1-C40 organosulfonyl groups.