期刊
HETEROCYCLIC COMMUNICATIONS
卷 23, 期 2, 页码 125-131出版社
WALTER DE GRUYTER GMBH
DOI: 10.1515/hc-2017-0034
关键词
C-13 NMR; 1-phenyl-3,5-diarylpyrazoles; 1-phenyl-3-t-butyl-5-arylpyrazoles; substituent effects
资金
- GSU Research Foundation
- Department of Chemistry
- NSF [1305041]
- Division Of Human Resource Development
- Direct For Education and Human Resources [1305041] Funding Source: National Science Foundation
A series of chalcones 1-12 were converted to pyrazolines (1Pi-12Pi) by reaction with phenylhydrazine followed by DDQ oxidation to produce the corresponding pyrazoles (1Pz-12Pz). Three 1-phenyl-3-t-butyl-5-arylpyrazoles (13Pz-15Pz) were synthesized using an analogous approach. Molecular modeling studies predicted the 5-aryl group of the pyrazoles for both series to have a torsion angle of 52 degrees-54 degrees whereas the 1-phenyl group was predicted to have 35 degrees-37 degrees torsion angles. The 3-aryl group was predicted to be essentially coplanar (-3 degrees) with the pyrazole system in the first series. C-13 NMR data for both series, 1Pz-12Pz and 13Pz-15Pz, were collected in DMSO-d(6) at 50 degrees C. A plot of the C4 chemical shifts for 1Pz-12Pz versus Hammet constants for 5-aryl substituents yielded a very good linear correlation (R-2 = 0.96) with a slope of 1.5. The chemical shift data for C4 showed little or no dependence on 3-aryl substituents. The result for 13Pz-15Pz, despite only three points, was consistent with the first series results and yielded a rho value of 2.0. Distal transmission of substituent effects (5-aryl groups) to C4 of the pyrazole system was reduced by roughly 50-60% of that of the analogous planar isoxazole system, but are not consistent with results for the similarly twisted 4-bromoisoxazoles.
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