2000 pyrazole derivatives

pyrazole derivativesR 0180

02 - 149Reaction of Aroyl-Substituted Heterocyclic Ketene Aminals withNitrile Imines: An Efficient Synthesis of Fully Substituted Pyrazolesand Evidence of Nucleophilic Addition of Enamines to 1,3-Dipoles.— Cycloaddition of heterocyclic aminals such as (I) and (IV) with the nitrileimine (II) affords the fully substituted pyrazoles (III) and (V). The reactionproceeds stepwise by nucleophilic addition forming a hydrazone intermediateand subsequent cyclization. In the case of nitrile imine (VII), hydrazones areobtained as the sole products. They can be cyclized to the correspondingpyrazoles, e.g. (IX), only under drastic conditions. — (LIU, BO; WANG,MEI-XIANG; HUANG, ZHI-TANG; Tetrahedron Lett. 40 (1999) 41, 7399-7402;Inst. Chem., Chin. Acad. Sci., Beijing 100080, Peop. Rep. China; EN)

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