Abstract: In the preparation of nitrenedipine by reaction of an ylidene compound of the formula ##STR1## with an enamine compound of the formula ##STR2## the improvement which comprises effecting the reaction in the presence of a catalytic amount of diisopropylamine acetate or dimethylbenzylamine acetate. The product is produced in high yield with reduced amounts of symmetrical by-products.

Abstract: In the preparation of a 1,4-dihydropyridine of the formula ##STR1## in which R is a phenyl radical which is optionally substituted once or twice by nitro and/or chlorine,R.sub.1 is a C.sub.1 -C.sub.4 -alkyl radical which is optionally substituted by a C.sub.1 -C.sub.4 -alkoxy group, andR.sub.2 is a C.sub.1 -C.sub.12 -alkyl radical which is optionally substituted by a C.sub.1 -C.sub.4 -alkoxy group, a trifluoromethyl group or the radical (C.sub.6 H.sub.5 CH.sub.2) (CH.sub.3)N,by preparing an ylidene compound of the formula ##STR2## and reacting such ylidene compound with an enamine compound of the formula ##STR3## the improvement which comprises preparing the ylidene compound by reaction of a ketocarboxylic ester of the formula ##STR4## with an aldehyde of the formula RCHO, in a solvent in the presence of a catalytic amount of any acetate salt of an amine, at a temperature from about -10.degree. C. up to 100.degree. C. The products symmetrical or unsymmetrical, are produced in high yield and purity.