Synthetic Routes to 4-Amino-Pyrazoles from Vinamidinium Salts

Significance

Reported are two new methods for the preparation of 4-aminopyrazoles. The first method involves the condensation of a vinami­dinium monohexafluorophosphate salt with a suitably protected hydrazine salt to give, following ­hydrolysis, the desired product in modest yield. The second method involves alkylation of a bromoacetanilide with 4-bromopyrazole, followed by a Pd(II)-catalyzed C-N coupling of the product with benzophenone imine. Subsequent acid-catalyzed cleavage provides access to the desired hydro­chloride salt of the 4-aminopyrazole. The latter synthetic route represents the first application of Buchwald amination chemistry to the synthesis of 4-aminopyrazole precursors.