The reaction sites of 3‐substituted pyrazolin‐5‐ones and their O‐ and N‐blocked analogues toward various isocyanates were investigated. 3‐Methyl and 3‐ethoxycarbonylpyrazolin‐5‐ones gave the corresponding 1‐carbamoylpyrazolinones, whereas the O‐alkylpyrazoles afforded 2‐carbamoylpyrazoles. On the other hand, the N‐alkylpyrazolinones were carbamoylated at 4‐position under drastic conditions.
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Mitsuhashi et al. (1982) studied this question.
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