| Abstract: | An Alternative Approach to the PQQ-Triester A novel approach to triethyl 5-methoxy-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylate ( 6 ), a close precursor of the redox cofactor PQQ of bacterial dehydrogenases, is described. Diethyl 2-oxopent-3-ynedioate ( 5 ) was used as building block for the annelation of the quinoline unit. The annelation proceeds in two steps via the diastereoselective formation of diethyl (Z)-4-{[2-(ethoxycarbonyl)-5-methoxyindol-6-yl]amiono}-2-oxopent-3-enedioate ((Z)- 7 ) followed by acid-catalyzed cyclocondensation. |
