Production of alk-1-en-5-ones and alk-1-en-5-als having the general formula (I): in which R1, R2 and R3 each denotes a hydrogen atom or a hydrocarbon radical having from one to 40 carbon atoms which may be joined together in pairs to form five-membered to sevenmembered rings and which may contain oxygen atoms as heteroatoms and in which R4 denotes a hydrogen atom or a hydrocarbon radical having one to 40 carbon atoms which may also contain oxygen atoms as heteroatoms. Said compounds I being formed by reacting an allyl alcohol having the formula (II): at a temperature of from 50* to 350* C. with an acyl malonate having the formula (III): in which the radicals R5 and R6 denote identical or different alkyl groups having from 1 to 8 carbon atoms, and the resultant intermediate product having the general formula (IV): is hydrolyzed and decarboxylated.