Synthesis and NMR‐Spectroscopic Investigations with 4‐Chloroacyl‐1‐phenylpyrazolin‐5‐ones

The synthesis of various 4‐acylpyrazolones bearing in the acyl moiety either a terminal chloro‐substituent or a terminal ortho‐chlorophenyl group was achieved by reaction of 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one (tautomer to 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐ol) with the corresponding acid chloride using calcium hydroxide / 1,4‐dioxane. In one case (reaction with chlorobutanoyl chloride) a spontaneous cyclization occurred leading to the corresponding oxepino2,3‐c]pyrazole. Detailed NMR spectroscopic investigations with all prepared compounds were performed.