QUINOLINE ALKALOIDS - SYNTHESIS OF PYRANO[2,3-B]QUINOLINES, KHAPLOFOLINE, LUNACRINE, AND DEMETHOXYLUNACRINE

Polyphosphoric acid (PPA)-catalyzed cyclization of 2-ono-3-vinylquinol inecarboxylic acid (1) yielded 3,4-dihydro-2,2-dimethyl-2H-pyrano[2,3- b]quinoline (4). The same reaction of 4-methoxy-2-oxo-3-vinylquinoline carboxylic acid (1g) afforded 4-methoxy-2,2-dimethylpyrano[2,3-b]quino line (4g), which on hydrolysis with ethanolic hydrochloric acid gave k haplofoline (5). The Prevost reaction of 4-methoxy-3-prenylquinolin-2- one (6) using I-2/HgO in acetic acid yielded 4-methoxy-2-isopropyIfuro [2,3-b]quinoline (7). Compound 7 on reduction with H-2/Pd-C followed b y N-methylation and de-O-methylation afforded lunacrine (10a). A simil ar reaction sequence on 6b gave demethoxylunacrine (10b).