1,4‐Cycloaddition reactions. III. Synthesis of furo[3,2‐c]pyrido[2,3‐g]quinolines, Furo[2,3‐a] [4,7]phenanthrolines, Furo[3,2‐c]pyrrolo[2,3‐g]quinolines, Furo[3,2‐c]pyrrolo[3,2‐g]quinolines, and Furo[3,2‐c]furo[2′,3′:4,5]pyrido[2,3‐g]quinolines from 2,3‐dihydro‐5‐methylfuran and schiff bases

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Abstract
The 1,4‐cycloaddition of 2,3‐dihydro‐5‐methylfuran (II) to 1‐acetyl‐1,2,3,4‐te trahydro‐6‐[(p‐hydroxybenzylidene)amino]quinoline (VIII) in the presence of boron trifluoride gave two pairs of epimers, namely dl‐10‐acetyl‐2,3,3a,4,5,7,8,9,10,11b‐decahydro‐4‐(p‐hydroxyphenyl)‐11b‐methylfuro[3,2‐c]pyrido[2,3‐g]quinoline (IXa and b) and dl‐8‐acetyl‐2,3,3a,4,5,8,9,10,11,‐11c‐decahydro‐4‐(p‐hydroxyphenyl)‐11c‐methylfuro[2,3‐a][4,7]phenanthroline (Xa and b). dl‐9‐Acetyl‐3,3a,4,5,7,8,9,10b‐octahydro‐4‐(p‐hydroxyphenyl)‐10b‐methyl‐2H‐furo[3,2‐c] pyrrolo‐[2,3‐g]quinoline (XIIIa) was the predominant product isolated from the reaction of II with 1‐acetyl‐5‐[p‐(hydroxybenzylidene)amino]indoline (XII). When 1‐acetyl‐6‐[(p‐hydroxybenzylidene)amino]indoline (XVI) was treated with 2,3‐dihydro‐5‐methylfuran (II), two epimers of dl‐7‐acetyl‐3,3a,4,5,7,8,9,10b‐octahydro‐4‐(p‐hydroxyphenyl)‐10b‐methyl‐2H‐furo[3,2‐c]pyrrolo[3,2‐g]quinoline (XVIIa and b) were obtained. dl‐2,3,3a,4,5,6b,8,9,9a,10,11,12b‐Dodecahydro‐4,10‐bis(p‐methoxyphenyl)‐6b,12b‐dimethylfuro[3,2‐c]furo[2′,3′:4,5]pyrido[2,3‐g]quinoline (XX) was formed when 2,3‐dihydro‐5‐methylfuran was allowed to react with N,N'‐bis(p‐methoxybenzylidene)‐p‐phenylcnediamine (XIX). Structure assignments were made from NMR spectra. None of the compounds exhibited appreciable biological activity.