5‐Halogen‐pyrazolcarbonsäuren

Abstract

Die 1,3-dipolare Cycloaddition von 3-Alkyl-bzw. 3-Aryl-4-halogensydnonen 1 mit Acetylendicarbonsaure-dimethylester in Xthylenglycol fiihrt zu I-alkylierten bzw. I-arylierten 5-Halogen-3,4-pyrazoldicarbonsiure-diestern 2, die bei Hydrolyse die entsprechenden Dicarbonsiiuren 3 liefern. Diese lassen sich selektiv zu I-Alkyl-bzw. I -Aryl-S-halogen-4-pyrazolcarbonsauren 4 decarboxylieren. 5-Halogenopynwlecarboxylic Acids')I ,3-Dipolar cycloaddition of 3-alkyl(or aryl)-4-halogenosydnones 1 to dimethyl acetylenedicarboxylate in ethylene glycol as solvent leads to the formation of I-alkylated(or arylated) S-halogen0-3,4-pyrazoledicarboxylates 2, which yield the corresponding dicarboxylic acids 3 on hydrolysis. These compounds can be selectively decarboxylated to I -alkyl(or aryl)-Shalogeno-4-pyrdzolecarboxylic acids 4.

Heterocyclic Analogues of Xanthone and Xanthione. 1H-Pyrano[2,3-c:6,5-c]dipyrazol-4(7H)-ones and Thiones: Synthesis and NMR Data

“…188 ºC (lit. [44] m.p. 187–188 ºC); 1 H-NMR (300 MHz, DMSO- d 6 ): δ (ppm) 12.97 (s, 1H, OH), 8.16 (s, 1H, H-3), 7.52–7.60 (m, 5H, Ph-H); 13 C-NMR (75 MHz, DMSO- d 6 ): δ (ppm) 162.3 (C=O), 142.4 (C-3, 1 J (C-3,H-3) = 193.5 Hz), 137.2 (Ph-C-1), 130.2 (C-5, 3 J (C-5,H-3) = 5.8 Hz), 129.3 (Ph C-3,4,5), 125.7 (Ph C-2,6), 112.3 (C-4, 2 J (C-4,H-3) = 8.9 Hz); 15 N-NMR (50 MHz, DMSO- d 6 ): δ (ppm) −160.8 (N-1), −70.2 (N-2).…”

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

“…As mentioned above, the thermal reaction of 3-alkyl-, 3-aryl- or even 3-substituted aminosydnones with symmetrical alkynes ( Scheme 1 ) represents a very useful and straightforward method for the synthesis of substituted 1,3,4-tri- or 1,3,4,5-tetrasubstituted pyrazoles [ 1 – 2 5 – 39 ] or indazoles.…”

“…act as the most common dipolarophiles because of their high reactivity. Moreover, one or both carboxylate groups in position 3 and 4 in the final pyrazole are easily removable using a hydrolysis/decarboxylation protocol [ 5 , 16 ] thus giving pyrazole-4-carboxylic acids – potent xanthine oxidoreductase inhibitors [ 40 ] or even 3,4-unsubstituted pyrazoles [ 16 ]. Both pyrazole carboxylic groups can be also modified to hydrazides and oxazole rings [ 26 ] or a new condensed pyridazine ring [ 27 ].…”

“…The most typical procedure involves heating both components in boiling hydrocarbon solvent (benzene, toluene or xylene) for several hours (up to 24 h) and the isolated yields are often close to 90% for the ordinary substituents (alkyls, aryls, halogens) of the sydnone. Somewhat lower yields were obtained in ethyleneglycol [ 5 ]. The reaction of the parent 1-phenylsydnone with DMAD and its diethyl analogue has also been performed in supercritical carbon dioxide [ 41 ] in which 65 and 83% yields of dimethyl (or diethyl) 1-phenylpyrazole-3,4-dicarboxylates were achieved.…”

Steric effects on the sydnones reactivity. New sydnones and pyrazoles

“…The 4-chloro-and 4-bromosydnones were found by Dickopp 14 to be unstable in non-polar solvents such that the corresponding pyrazoles were obtained in ethylene glycol upon reaction with excess DMAD. In our hands, 4-halogenosydnones 8a and 8b proved to be quite stable in xylene at reflux temperature and their reaction with a small excess of DMAD (1.2 molar ratio) led to the corresponding 5-halogenopyrazoles in yield of over 80%.In addition, 1-(4-Bromo-2-methylphenyl)-3,4-dicarboethoxy-5-iodopyrazole (9f) was obtained by 1,3-dipolar cycloaddition between 4-iodosydnone 8c and diethyl acetylenedicarboxylate.…”