A REGIOSELECTIVE ROUTE TO 3-ALKYL-L-ARYL-1H-PYRAZOLE-5-CARBOXYLATES -SYNTHETIC STUDIES AND STRUCTURAL ASSIGNMENTS

Ethyl 2,4-dioxooctanoate (1) was selectively protected as the 2-(metho xyimino) derivative 2. When 2 was reacted with phenylhydrazine hydroch loride, ethyl 3-butyl-1-phenyl-1H-pyrazole-5-carboxylate (4) was favor ed over the corresponding 5-butyl-1-phenyl-1H-pyrazole-3-carboxylate p roduct 5 by a ratio of at least 6:1, a complete reversal of the regios electivity observed for 1. The structures of 4 and 5 were assigned def initively by NOE difference experiments. Regiochemical and configurati onal assignments of the mono- and bis(methoxyimino) derivatives of 1 w ere also achieved by ID and 2D H-1 and C-13 nmr methods.