Pyrazolium-4-olates

The mesoionic type-B pyrazolium-4-olates 227 have been transformed with singlet oxygen to the dibenzoylhydrazine 229 (86CB762). It has been suggested that an intermediate 228 is formed and loses carbon monoxide (Scheme 40). 

Substitution at position 4 of the pyrazolium ring also gives mesomeric betaines, illustrated by the pyrazolium-4-olates 32. The structure and chemistry of these mesomeric betaines with general structure 34 are different to those of the type A compounds, and are referred to as type B mesoionic compounds. They often react via an acyclic valence tautomer (see Section 2.4.5). 

Dithiolium salts react with hydrazines similarly to amines, but further cyclization gives pyrazoles (46) or pyrazolium salts (47). When there are replaceable substituents, hydrazones and azines are formed. A mesoionic l,2-dithiole-3-olate (20 R = Ph) reacts similarly at C(3) with aniline, but with eventual formation of the products (48) and (49) <87CJC2830,92T8127). The reaction... 

Aryl-l,2-dithiolium-Salze und 1,2-disubstituierte Hydrazine dienenzur Herstellung von 1,2-disubstituierten Pyrazolium-Salzen996,1381. Aus 3,5-Diphenyl-l,2-dithiolium-4-olat und einem Hydrazin-Hydrat-OberschuB wird in ethanolischer Losung durch Erhitzen 3,5-Diphenyl-4-hydroxy-lH-pyrazol (90% Schmp. 239°) gebildet997 ... 

Bei 3,5-Dimethoxy-4-phenyl-lH-pyrazol gelingt mit Chlorcarbonyl-phenyl-keten (5 min in Di-ethylether) der RingschluB zu 5,7-Dimethoxy-2,6-diphenyl-l-oxo-lH-(j)yrazolio[l,2-a]pyrazo-liumy-3-olat (Schmp. 150°)2388, analog reagieren eine Rcihe weiterer 1-unsubstituierter 1H-Pyrazole mit Chlorcarbonyl-ketenen oder Kohlensuboxid zu den mesomeren Betain-Strukturen der 1 H--3-olate2389 2399 2400-2403. 

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