Dimethyl Sulfate → 1-Methyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one

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The pyrazolinone prepared as described above in (a) (1.153 g, 7.2 mmol) in dry toluene (3 ml) was treated with dimethyl sulphate (8 mmol, 750 μl) and the whole refluxed under nitrogen for 5 hours. The reaction mixture was then allowed to cool and in doing so separated into two phases. The upper consisting mainly of toluene was carefully pipetted off and discarded. The remaining layer was then treated with water (1 ml), the whole warmed with stirring to 50° C. and then treated with 40% sodium hydroxide solution (1 ml) and stirred at 50° C. for a further 30 minutes. The resultant solution was subsequently extracted with three portions of benzene. The first two extracts were found to contain two products which has spectral properties consistent with 2-methyl-1-phenyl-3-pyrazolin-5-one and 2,4-dimethyl-1-phenyl-3-pyrazolin-5-one. These were separated by chromatography on silica (ethyl acetate) to give 2-methyl-1-phenyl-3-pyrazolin-5-one (95 mg). The third extracton (above) consisted solely of 2-methyl-1-phenyl-3-pyrazolin-5-one (208 mg) (Total yield, 24%). νmax (CHCl3) 1655, 1595, 1550, 1495 cm-1. δ(D6Acetone) 3.11 (3H, s, --NMe), 5.44 (1H, d, J4 Hz, C4 proton), 7.47 (5H, m, phenyl protons), 7.83 (1H, d, J4 Hz, C3 proton). Found: M+ 174.0798; C10H10N2O requires M; 174.0794.

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