[Chemistry and pharmacology of pyran derivatives. XVII. Synthesis of 2-(dialkylamino)-5-hydroxychromones and their transformation to derivatives of 2H-pyran[4,3,2-de]-1-benzopyran].

Through the reaction of resorcin with N,N-dialkylethoxy-carbonylacetamides in suitable conditions 2-(dialkylamino)-5-hydroxychromones (II) were available. Transformation of these compounds into [5-acetoxy-2-(dialkylamino)-4H-chromen-4-ylidene] malononitriles (VII) by reaction with malononitrile in acetic anhydride and treatment of (VII) with hydrochloric acid gave rise to the formation of 5-(dialkylamino)-2-imino-2H-pyrano [4,3,2-de]-1-benzo-pyrans (VIII). Furthermore 5-hydroxychromones (II) when treated with methyl iodide gave the corresponding 5-methoxychromones (III) which in turn yielded 4H-chromen-4-ylidene derivatives (X) by reaction with malononitrile in acetic anhydride. The hydrolysis of the latter compounds with hydrochloric acid resulted in the formation of 2-(dialkylamino)-4-methyl-5-methoxychromenilium salts (XI). Among the compounds which were submitted to pharmacological screening for their antiallergic properties 5-methoxychromone (III a) and 2H-pyrano [4,3,2-de]-1-benzopyran (VIII b) showed a notable activity but also high toxicity.