HCID 23454278, compound → 5,6,7,8-tetrahydro-8-hydroxy-2-quinolone

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Reaction Steps

Starting materials for the preparation of the ketone of the invention are 8-chloro-5,6,7,8-tetrahydro-2-quinolone hydrochloride or 8-bromo-5,6,7,8-tetrahydro-2-quinolone hydrobromide, which are hydrolyzed with the 4- to 8-fold amount of water, at a temperature of from 50° to 100° C., preferably 80° to 100° C., to form 8-hydroxy-5,6,7,8-tetrahydro-2-quinolone which, after cooling of the neutralized solution (neutralization for example by means of ammonia) precipitates in crystallized form as trihydrate. In order to prepare the ketone of the invention, it is however required to oxidize the anhydrous 8-hydroxy-5,6,7,8-tetrahydro-2-quinolone with manganese dioxide. The necessary dehydration of the trihydrate formed first is generally carried out by distillation removal of the hydration water as azeotropic mixture with, for example, butyl acetate, chloroform, butanol, toluene or cyclohexanone. Butyl acetate and cyclohexanone have proved to be especially suitable as agents for forming an azeotropic mixture (=water entrainers), because they allow particularly economic operations due to their good dissolving power, relatively high boiling point and minimal miscibility with water.

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