O-Phenylenediamine → 2-(2-Chloro-6-tert-butylpyridin-3-yl)benzimidazole

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Reaction Conditions

Reaction Steps

A mixture, homogenised in a mortar, of 19.5 g (100 mmol) of 2-chloro-3-cyano-6-tert-butylpyridine (S28), 36.2 g (200 mmol) of o-phenylenediamine and 38.0 g (200 mmol) of p-toluenesulfonic acid monohydrate is heated at 220° C. (oil-bath temperature) for 3 h. After cooling, the black, glassy sinter cake is taken up in a mixture of 100 ml of ethanol and 100 ml of 1N hydrochloric acid with vigorous stirring. After stirring for 30 min., the grey-green solid is filtered off with suction, washed three times with 50 ml of water each time and dried in vacuo. The solid is taken up in 200 ml of ethyl acetate, chromatographed on silica gel (ethyl acetate/heptane 1:1, Rf about 0.7) in order to remove 2-tert-butyl-6,11-dihydrobenzo[b]pyrido[2,3-e]-1,4-diazepin-5-one and brown by-products. The crude product obtained in this way is dissolved in ethyl acetate at the boiling temperature, and four times the amount of cyclohexane is added dropwise. After stirring at room temperature for 18 h, the crystals formed are filtered off with suction, washed with n-heptane and dried in vacuo. Yield: 7.5 g (26 mmol), 26%. Purity: >95% according to 1H-NMR.

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