A novel process is provided for the preparation of 6,7-dimethoxy-4-amino-2¢4-(2-furoyl)-1-piperazinyl!quinazoline. It includes as a final step, cyclizing methyl-N-(3,4-dimethoxy-6-cyanophenyl)-¢4-(2-furoyl)-1-piperazinyl! thioformamidate by heating, together with ammonia, in a polar solvent, in the presence of an alkali metal amide. The methyl-N-(3,4-dimethoxy-6-cyanophenyl)-¢4-(2-furoyl)-1-piperazinyl!thioformamidate is preferably formed by reacting 3,4-dimethoxy-6-¢4-(2-furoyl)-1-piperazinyl-thiocarbamido!benzonitrile with methyl chloride. By this process the quinazoline ring in prazosine is produced within the molecule, rather than in a reaction between two different molecules.
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