Phosphoric Acid → 6-phenyl-8-chloro-4H-s-triazolo[4,3-a][1,4]benzodiazepine-1-carboxaldehyde-diethylacetal

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Reaction Steps

A mixture of 300 mg of 6-phenyl-8-chloro-4H-s-triazolo[4,3-a][1,4]benzodiazepine-1-methanol, 0.57 g of dicyclohexyl-carbodiimide, 45 mg of phosphoric acid and 3 ml of abs. dimethylsulphoxide is stirred for 6 days at 25° and for a further 2 days at 70°-80°. Methylene chloride is then added, the organic phase washed with water and saturated sodium chloride solution, dried over magnesium sulphate and concentrated by evarporation. Crude 6-phenyl-8-chloro-4H-s-triazolo[4,3-a][1,4]benzodiazepine-1-carboxaldehyde is obtained, which is dissolved in 5 ml of ethanol. An addition is made to the obtained solution of 100 mg of p-toluenesulphonic acid, and the mixture refluxed for 10 hours. The solution is concentrated in vacuo. The residue is taken up in methylene chloride, the organic phase washed with 5% aqueous potassium carbonate solution and with saturated sodium chloride solution, dried over sodium sulphate, and concentrated by evaporation. The residue is recrystallised from ethyl acetate/ether/petroleum ether to obtain 6-phenyl-8-chloro-4H-s-triazolo[4,3-a][1,4]benzodiazepine-1-carboxaldehyde-diethylacetal, M.P. 133°-135°.

Provenance & Evidence