METHOD OF SYNTHESIS OF PYRAZOLE AND ITS DERIVATIVES Russian patent published in 1999 - IPC

FIELD: organic chemistry and technology. SUBSTANCE: invention describes a method of synthesis of pyrazole and its derivatives of the formula (I) where radicals R¹,R²,R³ and R⁴ mean hydrogen atom or direct or branched alkyl-group, preferably C₁-C₁₀-alkyl- -group, more preferably C₁-C₈-alkyl-group and the most preferably C₁-C₆-alkyl-group. These groups can be broken by heteroatoms, for example, nitrogen, oxygen and sulfur atoms and can have substituents taken from the group involving nitro-, carboxyl-, sulfonyl-group, halogen atom, cycloalkyl-, bicycloalkyl-, aryl- and heteroaryl-group; cycloalkyl-group or bicycloalkyl-group, preferably C₃-C₈-cycloalkyl-group or C₆-C₁₀-bicycloalkyl-group. These groups can be broken by heteroatoms, for example, nitrogen, oxygen and sulfur atoms and can have substituents taken from the group involving nitro-, carboxyl-, sulfonyl-group, halogen atom, alkyl-, cycloalkyl-, bicycloalkyl-, aryl- and heteroaryl-group; aryl- or heteroaryl-group, for example, phenyl-, naphthyl- and pyridyl-group. These groups can have substituents taken from the group involving nitro-, carboxyl-, sulfonyl-group, halogen atom, alkyl-, cycloalkyl-, bicycloalkyl-, aryl- and heteroaryl-group. Synthesis is carried out using α,β--unsaturated carbonyl compound of the formula (II) where R¹,R² and R³ have values indicated above and hydrazine or its derivatives of the formula (III) H₂N-NHR⁴ (III) where R⁴ has the above indicated values. Method involves the use of sulfuric acid and iodine or a compound releasing iodine or hydrogen iodide. At first, α,β-unsaturated carbonyl compound of the formula (II) is interacted with hydrazine or its derivative of the formula (III) without a solvent addition and at the absence of sulfuric acid and obtained reaction mixture is subjected for interaction at the following stage with a mixture consisting of sulfuric acid and iodine or a compound releasing iodine or hydrogen iodide. EFFECT: simplified method, increased yield and purity degree of pyrazole and its derivatives. 6 cl, 5 ex