Process for the preparation of linear 1,3-diketones

A process for the preparation of a linear 1,3-diketone of formula I ##STR26## wherein R.sub.1 and R.sub.2 are each independently of the other C.sub.1 -C.sub.20 alkyl, phenyl or phenyl which is substituted by halogen, hydroxy, NO.sub.2, C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkoxy, or are C.sub.7 -C.sub.9 phenylalkyl or a radical of formula II

• --A--X--R.sub.4 (II)
• wherein
• A is C.sub.1 -C.sub.12 alkylene, phenylene or phenylene which is substituted by halogen, hydroxy, NO.sub.2, C.sub.1 -C.sub.4 alkyl and/or C.sub.1 -C.sub.4 alkoxy, or is C.sub.1 -C.sub.12 alkylene which is substituted by hydroxy, halogen and/or alkoxy,
• X is oxygen or sulfur, and
• R.sub.4 is hydrogen, C.sub.1 -C.sub.18 alkyl, phenyl or phenyl which is substituted by halogen, hydroxy, C.sub.1 -C.sub.4 alkyl, NO.sub.2 and/or C.sub.1 -C.sub.4 alkoxy, or is C.sub.7 -C.sub.9 phenylalkyl, and
• R.sub.3 is hydrogen, C.sub.1 -C.sub.20 alkyl, phenyl or phenyl which is substituted by halogen, hydroxy, C.sub.1 -C.sub.4 alkyl, NO.sub.2 and/or C.sub.1 -C.sub.4 alkoxy, or is C.sub.7 -C.sub.9 phenylalkyl, by a Claisen condensation of a ketone of formula III ##STR27## with an ester of formula IV ##STR28## wherein R.sub.5 is C.sub.1 -C.sub.5 alkyl, phenyl or phenyl which is substituted by halogen, C.sub.1 -C.sub.4 alkyl or hydroxy;
• or, when R.sub.2 in formula I is --(CH.sub.2).sub.m OH, also with a cyclic ester of formula V ##STR29## in which m is 2 to 10, in the presence of a C.sub.1 -C.sub.5 alcoholate of an alkali metal or alkaline earth metal as base, which process comprises
• carrying out the reaction in a mixture of dimethyl sulfoxide and at least one organic solvent which is inert under the reaction conditions which inert solvent is selected from the group consisting of dioxane, tetrahydrofuran, diethylene glycol dimethyl ether, methyl tert-butyl ether, toluene and N-methylpyrrolidone and in which process the Claisen condensation reaction is carried out in the temperature range from -20.degree. to +70.degree. C.