Hydrochloric Acid → (4s,7r)-2-Phenyl-7,8,8-trimethyl-1,2,4,5,6,7-hexahydro-4,7-methano-indazol-3-one

Participants

Reaction Steps

A solution of (1R,4R)-4,7,7-trimethyl-3-oxo-bicyclo[2.2.1]heptane-2-carbonyl chloride (Intermediate 20; 4.36 g, 20.3 mmol) in 1,2-dichloroethane (40 mL) was added over a period of one minute to a cooled (˜0° C.) solution of N-ethylidene-N′-phenyl-hydrazine (prepared according to A. R. Maguire et al. Bioorg. Med. Chem. 2001, 9, 745-762; 2.60 g, 19.4 mmol) and pyridine (2.5 mL, 30.9 mmol) in 1,2-dichloroethane (20 mL). The reaction mixture was stirred at room temperature for 15 min and then at 50° C. for 25 min. It was then cooled to room temperature and 4M HCl in dioxane (12 mL) was added. The reaction mixture was stirred for 5 min at room temperature, then glacial acetic acid (20 mL) was added and the mixture was heated in an oil bath at 100° C. for 20 min. The reaction mixture was cooled to room temperature and then evaporated. Dichloromethane (200 mL) was added, the solution was washed with 50% saturated brine (2×50 mL), and the combined aqueous layers were back-extracted with dichloromethane (2×100 mL). The combined organic layers were washed with brine (150 mL), dried (magnesium sulfate), filtered, evaporated and eluted through a plug of silica gel with 30% ethyl acetate/hexanes to give (4S,7R)-2-phenyl-7,8,8-trimethyl-1,2,4,5,6,7-hexahydro-4,7-methano-indazol-3-one (5.04 g, 97%) as an orange foam.

Provenance & Evidence