General Papers ARKIVOC 2007 (xvi) 83-91
employing active methylene compounds possessing a-cyano or a-keto group using a previously reported protocol. 21-24
Results and Discussions
Compound 1 was prepared by cyclocondensation of ethyl benzoylacetate with salicylaldehyde25. Compound 1 was then allowed to react with malononitrile in refluxing ethanol containing a catalytic amount of piperidine to give 2-amino-5-oxo-4-phenyl-5,10b-dihydropyrano[3,4-c]chromene- 1-carbonitrile 2. The same product was obtained when malononitrile19 was replaced with cyanoacetamide (Scheme 1).
O Ph O O O Ph O O NH2 NC CH2(CN)2 EtOH/Pip. 1 O Ph O O NC NH2 O O Ph O O NH2OH NC H NCCH2CONH2 EtOH/Pip. 2
Scheme 1
Treatment of compound 1 with ethyl cyanoacetate under basic conditions, unexpectedly afforded ethyl 10-cyano-9-hydroxy-6-oxo-7-phenyl-6H-benzo[c] chromene-8-carboxylate 3. The reaction pathway is assumed to proceed by nucleophilic addition of the carbanion to the ethylenic bond of compound 1 affording the expected pyranochromene. Which in turn reacts with a second equivalent of ethyl cyanoacetate ion. Subsequent ring opening followed by recyclization and elimination of HCN affords the isolated product 3.
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