Procedure for the synthesis of - indolenina 2,3,3 Trimethyl

摘要

A process for the preparation of substituted indolenines of the formula: IMAGE IV wherein R is hydrogen, alkyl, aryl or cycloalkyl, halogen, or a functional group selected from among cyano, hydroxyl, alkoxy, nitro or sulphonic groups, and wherein R1, R2 and R3 are the same, or different, and are selected from alkyl, aryl or cycloalkyl radicals, comprising reacting in the presence of an organic solvent an aromatic amine of the formula: IMAGE I with a tertiary hydroxyketone of the formula: IMAGE II wherein R, R1, R2 and R3 have the same meanings as defined above, in the presence of a catalyst selected from mineral acids, organic acids, Lewis acids or ionic exchange resins in acid form, and wherein said aromatic amine is slightly in excess, to form first an imine of the formula: IMAGE III under reaction conditions wherein the solvent is removed by azeotropic distillation, and thereafter continuing the reaction to remove water and cyclizing to the desired indolenines. In a preferred embodiment, 2,3,3-trimethylindolenine is prepared by reacting an excess of aniline with 3-methyl-3-hydroxybutan-2-one in the presence of ZnCl2 as catalyst utilizing benzene as solvent. The substituted indolenines obtained are useful in production of dyes and other compounds useful in the dyeing and photographic industries.