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

Participants

Reaction Steps

Triethylamine (440 μL, 3.2 mmol) was added to solution of (1S,4S)-4,7,7-trimethyl-3-oxo-bicyclo[2.2.1]heptane-2-carbonyl chloride (Intermediate 25; 329 mg, 1.5 mmol) in 1,2-dichloroethane (6 mL) over 1 min. Then a solution of N-benzyl-N′-(2,3-dimethyl-phenyl)-hydrazinecarboxylic acid tert-butyl ester (450 mg, 1.38 mmol) in 1,2-dichloroethane (12 mL) was added over 2 min. The reaction mixture was stirred at room temperature for 15 min and then heated in an oil bath at 50° C. for 2 h and then at 60° C. for 1 h. A solution of HCl in dioxane (4 M; 8 mL, 32 mmol) was added and the mixture was heated in an oil-bath at 100° C. for 1 h. The reaction mixture was allowed to cool, silica gel was added, the solvent was evaporated and the mixture was purified using an ISCO 40 g column, eluting with 60-100% ethyl acetate/hexanes and then 5% methanol/dichloromethane. Fractions homogeneous for the product were evaporated, and then treated with methanol and charcoal. This mixture was stirred for 20 min, filtered through Celite and evaporated to give an orange gum. The gum was purified for a second time using an ISCO 40 g column, eluting with 2-4% methanol/dichloromethane. Fractions homogeneous for the product were evaporated, co-evaporated with diethyl ether and petroleum ether, and then dried under high vacuum at room temperature to give (4R,7S)-1-benzyl-2-(2,3-dimethyl-phenyl)-7,8,8-trimethyl-1,2,4,5,6,7-hexahydro-4,7-methano-indazol-3-one (57 mg, 11%) as an off-white foam. ES(+)-MS (M+H) 387.

Provenance & Evidence