A. 2-Hydroxymethylenecyclohexanone, Method 1. A mixture of 23 g. (1 g. atom) of sodium metal cut in approximately 1-cm. cubes, 2 l. of dry ether, 98 g. (103 ml., 1 mole) of redistilled cyclohexanone, and 110 g. (120 ml., 1.5 moles) of ethyl formate is placed in a 5-l. three-necked flask equipped with a stirrer, stopper, and vent tube. The reaction is initiated by the addition of 5 ml. of ethyl alcohol to the stirred mixture, which is then placed in a cold water bath. Stirring is continued for 6 hours. After standing overnight, 25 ml. of ethyl alcohol is added, and the mixture is stirred for an additional hour. After the addition of 200 ml. of water, the mixture is shaken in a 3-l. separatory funnel. The ether layer is washed with 50 ml. of water, and the combined aqueous extracts are washed with 100 ml. of ether. The aqueous layer is acidified with 165 ml. of 6N hydrochloric acid, and the mixture is extracted twice with 300 ml. of ether. The ether solution is washed with 25 ml. of saturated sodium chloride solution and then is dried by the addition of approximately 30 g. of anhydrous magnesium sulfate powder. The drying agent is removed by suction filtration, and the ether is evaporated on the steam bath. The residue is distilled under reduced pressure using a 6-inch Vigreux column. After a small fore-run there is obtained 88–94 g. (70–74%) of 2-hydroxymethylenecyclohexanone, b.p. 70–72°/5 mm., n_D25 1.5110 (Note 1).

2-Hydroxymethylenecyclohexanone, Method 2. A mixture of 50 g. (1 mole) of 48% sodium hydride dispersed in mineral oil (Note 2), 2 l. of dry ether, and 5 ml. of ethyl alcohol is placed in a 5-l. three-necked flask equipped with a stirrer, dropping funnel, and vent tube. The reaction vessel is cooled by means of a cold water bath, and a solution of 98 g. (103 ml., 1 mole) of redistilled cyclohexanone and 110 g. (120 ml., 1.5 moles) of ethyl formate is added dropwise during 1 hour. Stirring is continued for 6 hours (Note 3), and the solution is allowed to stand overnight. After the addition of 20 ml. of ethyl alcohol, the mixture is stirred for 1 hour. Water (200 ml.) is added to the flask with stirring, the mixture is shaken in a 3-l. separatory funnel and the organic layer separated. The product is isolated according to the procedure described in Method 1. The yield of 2-hydroxymethylenecyclohexanone is the same by both methods.

B. 4,5,6,7-Tetrahydroindazole. A solution of 63 g. (0.5 mole) of 2-hydroxymethylenecyclohexanone and 500 ml. of methyl alcohol contained in a 2-l. beaker is treated with 25 ml. (0.5 mole) of hydrazine hydrate in small portions (Note 4). After standing for 30 minutes the mixture is concentrated by warming under reduced pressure on the steam bath. To aid in removing the water, 100 ml. of ethyl alcohol is added, and again the mixture is concentrated by heating under reduced pressure. The residue is dissolved in about 100 ml. of hot petroleum ether (Note 5), and after cooling in an ice bath for 1 hour the solid that separates is collected by suction filtration and washed with a small amount of cold petroleum ether. The crude 4,5,6,7-tetrahydroindazole, m.p. 79–80°, weighs 58–60 g. (95–98%) and is sufficiently pure to be used in the next step (Note 6) and (Note 7).

C. Indazole. A mixture of 50 g. (0.41 mole) of 4,5,6,7-tetrahydroindazole, 35 g. of 5% palladium on carbon (Note 8) and 1 l. of dry decalin is placed in a 3-l. round-bottomed flask and heated under reflux for 24 hours. The hot mixture is filtered by suction, using a previously heated Büchner funnel, and the filtrate is allowed to cool. After standing overnight, the indazole that separates is collected by suction filtration, washed with 100 ml. of petroleum ether, and air-dried. The solid is dissolved in 750 ml. of hot benzene, and about 4 g. of decolorizing carbon is added. The mixture is filtered through a fluted filter paper and then is refiltered, using the same filter paper. Two liters of warm petroleum ether is added, and the solution is cooled in an ice bath for 2 hours. The indazole (m.p. 146–147°) is collected by suction filtration and after air drying weighs 24–25 g. (50–52%).