GB865709A - Pyrazole compounds and the preparation thereof - Google Patents

Abstract

The invention comprises 3-amino-2-aryl-pyrazoles unsubstituted in the 4- and 5-positions, the corresponding 3-amino-2-aryl-1, 5-dihydro-pyrazoles and acid addition salts thereof, and a process for the preparation of the 3-amino-2-aryl-pyrazoles by intromolecularly condensing N-(b -cyanoethyl)-N1-aryl-hydrazine in the presence of an oxidising agent e.g. hydrogen peroxide, ferric salts such as ferric sulphate or ferric chloride, or a mixture of hydrogen peroxide and ferric salts. This process may be carried out in one or two steps, in the latter case the condensation is carried out in the presence of an acid as well as the oxidising agent to form an intermediate product which may or may not be isolated, and ring closure is then carried out with an alkaline agent. The pyrazoles may also be obtained by the hydrolysis and decarboxylation of the corresponding 4-carbethoxy compounds. The 1, 5-dihydro-pyrazoles may be prepared by the above intramolecular condensation process without the use of the oxidising agent. Detailed examples are given describing the preparation of 3-amino-2-phenyl-pyrazole and the corresponding 1, 5-dihydropyrazole. N-Phenyl-N1-(b -cyanoethyl)-hydrazine is prepared by refluxing phenyl hydrazine and acrylonitrile. 2-Phenyl-3-amino-4-carbethoxpyrozole is prepared by reacting ethoxymethylene-cyanacetic acil ethyl ester with phenyl hydrazine.