Process for the preparation of carboxylic acids and derivatives of them

A process for the preparation of carboxylic acids, and their derivatives, of the formula ##STR18## wherein R means hydrogen, or a C.sub.1-4 alkyl or a (C.sub.1-5 alkoxy)carbonyl group,

• R.sub.1 stands for a C.sub.1-6 alkyl group, a (C.sub.1-5 alkoxy)-carbonyl group, a (C.sub.1-5 alkyl)carbonyl group, a (C.sub.1-5 alkoxy)carbonyl(C.sub.1-5 alkyl) group, a phenyl group, optionally monosubstituted by a C.sub.1-4 alkyl or C.sub.2-4 alkenyl group, di- or tri- substituted by C.sub.1-4 alkoxy groups, monosubstituted by a nitro group, disubstituted by C.sub.1-4 alkoxy and hydroxy groups, monosubstituted by a C.sub.1-4 alkylthio group, mono-or disubstituted by one or two di(C.sub.1-4 alkyl) amino groups or monosubstituted by halogen, for a furyl group, for a thiofuryl group, for a thienyl group, or for a group of the formula ##STR19## or R and R.sub.1 together form a straight-chain C.sub.4-5 alkylene group, R.sub.7 stands for hydrogen or a C.sub.1-7 alkyl group and
• R.sub.8 means hydrogen or a carboxyl group,
• which process comprises reacting a 1,3-dioxane-4,6-dione derivative of the formula ##STR20## wherein R.sub.9 stands for a C.sub.1-4 alkyl group or a phenyl group, optionally monosubstituted by halogen, and
• R.sub.10 stands for hydrogen or a C.sub.1-5 alkyl group, or
• R.sub.9 and R.sub.10 together form a pentamethylene group,
• and an aldehyde or ketone of the formula ##STR21## wherein R and R.sub.1 are as defined above,
• in the presence of formic acid and of 1 or more members selected from the group consisting of secondary amines and tertiary amines and, optionally of an alcohol of the formula
• R.sub.7 --OH VI,
• wherein
• R.sub.7 is a C.sub.1-7 alkyl group,
• at a temperature of 20.degree. to 140.degree. C. optionally in the presence of an inert organic solvent.