Hydrazine hydrate (1:1) → ethyl 4,5,6,7-tetrahydro-1H-indazole-3-carboxylate

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Reaction Steps

A solution of oxo-(2-oxo-cyclohexyl)-acetic acid ethyl ester [7.5 g, Reference Example 19(a)] in acetic acid (150 ml) was treated dropwise with hydrazine monohydrate (1.65 ml). The mixture was refluxed for 8 hours, then cooled and then evaporated. The residue was partitioned between ethyl acetate (200 ml) and saturated sodium bicarbonate solution (200 ml) and the organic layer was dried over sodium sulfate and then evaporated. The residual orange oil was subjected to flash column chromatography on silica eluting with a mixture of ethyl acetate and hexane (1:1, v/v) to give 4,5,6,7-tetrahydro-1H-indazole-3-carboxylic acid ethyl ester (606 mg) as an orange oil which solidified on standing. LC-MS (METHOD B): RT=2.79 minutes; 195 (M+H)+. (b) 5-Isopropyl-1H-pyrazole-3-carboxylic acid ethyl ester

Provenance & Evidence