Phosgene → 4,5-dihydro-5-methyl-6-[p-(prop-2-ynyloxycarbonylamino)-phenyl]-3(2H)-pyridazinone

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Reaction Steps

2.8 g (49.9 millimoles) of prop-2-ynol are added dropwise to a stirred solution of 9.9 g (100 millimoles) of phosgene in 100 ml of absolute ether at -10° C. and the reaction solution is then stirred for 1 hour at the same temperature. Thereafter it is stirred for one hour at room temperature and the excess phosgene is then removed by means of a dry stream of nitrogen, after which the ether is removed under reduced pressure at room temperature. The prop-2-ynyl chloroformate which remains (5.2 g) is added, at room temperature, to a solution, prepared by the method described in Example 31, of 5.0 g (24.6 millimoles) of 6-(p-aminophenyl)-4,5-dihydro-5-methyl-3(2H)-pyridazinone in 150 ml of absolute tetrahydrofuran. The reaction mixture is then refluxed for 1 hour and concentrated to about 70 ml. Water is added and the product is filtered off and recrystallized first from ethanol/water, then from acetone/water and finally from ethanol, giving 2.9 g (41% of theory) of 4,5-dihydro-5-methyl-6-[p-(prop-2-ynyloxycarbonylamino)-phenyl]-3(2H)-pyridazinone as colorless crystals, of melting point 204°-205° C.

Provenance & Evidence