4-Acyl-5-methyl-2-phenylpyrazolones: NMR and X-Ray Structure Investigations

H-and "c-NMR investigations with 4-acyl-5-methyl-2-phenyl-1,2dihydro-3H-pyrazol-3-ones (1-6) are presented, indicating these compounds to exist predominantely as hydroxypyrazoles in CDC13 or benzene-d6 solution, whereas in DMSO-d6 also a considerable amount of NH tautomer is present.X-Ray crystal analyses revealed that in the solid state the 4-propionyl compound (2) is present as hydroxypyrazole, the 4-(Zthienyl) derivative (6) as NH isomer and the Ccinnamoyl product (4) to have an exocyclic double bond structure stabilized by an intramolecular hydrogen bond.Cyclisation of the latter compound (4) in acidic medium leads to the formation of 3-methyl-l,6-diphenyl-5,6-dihydro-Further details of the crystal structure investigations are available from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany), on quoting the depository numbers CSD-408990 (4).408991 (6), and 408992 (2).