582298-00-8

Upstream product

• 98790-58-0 ethyl (Z)-4-hydroxy-2-oxopent-3-enoate 
• 582297-95-8 CH₃O₄S^(1-)*C₁₄H₁₇N₂O₂⁽¹⁺⁾ 
• 100-63-0 phenylhydrazine 
• 81153-64-2 5-methyl-1-phenyl-1H-pyrazole-3-carboxylic acid ethyl ester 

Downstream Products

• 28022-64-2 2,5-dimethyl-1-phenyl-1H-pyrazole-3-thione 

Relevant academic research and scientific papers

Functionalized 4-aminoquinolines by rearrangement of pyrazole N-heterocyclic carbenes

(Figure Presented) Thermal decarboxylation of 1-phenyl pyrazolium-3- carboxylates from the mesomeric betaine class of substances leads to pyrazole-N-heterocyclic carbenes, which immediately rearrange to multiply substituted 4-aminoquinolines (see scheme). These species are of interest for the synthesis of heterocycles and pharmacologically active compounds.

New pyrazolium-carboxylates as structural analogues of the pseudo-cross-conjugated betainic alkaloid nigellicine

Pyrazolium-3-carboxylates were examined as relatives of the betainic alkaloid Nigellicine and as new examples of the sparsely populated class 16 of heterocyclic pseudo-cross-conjugated mesomeric betaines (PCCMB). The title compounds were prepared in a 4-step procedure starting from β-diketo compounds 8 which were cyclized with substituted hydrazines. The resulting isomeric pyrazole esters 9 and 10 were separated and subsequently quaternized with dimethyl sulfate in the presence of nitrobenzene to pyrazolium esters 11 and 12. Saponification was best accomplished in diluted sulfuric acid, which resulted in the formation of the pseudo-cross-conjugated mesomeric betaines 13 and 14 in one step. Protonation to the corresponding carboxylic acids required the treatment of the betaines with tetrafluoroboric acid in dichloromethane. The effect of negative solvatochromism proves the charge separation in the ground state of the molecules. X-ray crystallographic analyses, semiempirical calculations, and ESI mass spectrometric measurements were performed to gain knowledge about the phenomenon of pseudo-cross-conjugation.