Three component condensation of active methylene compounds with aniline and trialkyl orthoformate gives anilinomethylene-1,3-dicarbonyls, which can be hydrolysed with aqueous K2CO3, KOH or HCl, depending on the sensitivity of the hydroxymethylene derivative thus formed. The reactions sequence is fairly generally applicable: Cyclohexan-1,3-diones, pyrimin-3,5-diones (including barbituric acids), pyrazolones and pyrazolin-3,5-diones, indan-1,3-dione, (thio)phthalide, indoxyl, oxindole, anthrone, 2,6- and 2,7-dihydroxynaphthalene, and pentan-2,4-dione have been formylated. Using orthoacetate or orthopropionate, tetronic acid, pyrazolones and pyrazolin-3,5-diones,resp.,could also be acylated by this method.