Experiments on the Synthesis of dl-Camptothecin. III. Total Synthesis of dl-Camptothecin

dl-Camptothecin (XXX) and two epimeric N-formyl-1, 2, 6, 7-tetrahydrocamptothecins (XXIIIa, b) have been synthesized from 3-oxo-1H-pyrrolo [3, 4-b] quinoline IIIa by using following two key reactions. 1) An intramolecular aldol condensation of the imido-ester (VIIIb→IXb). 2) Vilsmeier reaction on a 4-methoxy-2-pyridone ring (XVIb→XVII) followed by nucleophilic attack of a malonate carbanion onto the formyl-pyridone ring (XVII→XVIII).