QUINOLINONE CYCLOADDITION AS A POTENTIAL SYNTHETIC ROUTE TO DIMERIC QUINOLINE ALKALOIDS

Acid-catalysed dehydration of the quinolinone allylic alcohol 24 and c oncomitant Diels-Alder cycloaddition of the resulting diene 25 under a cid conditions, followed by further intramolecular cyclization, led to the isolation of isomeric tetracyclic compounds containing one quinol in-2-one and one quinolin-4-one ring (dimer A, 27 and dimer C, 30). Fu rther intramolecular cyclization of dimer A 27 yielded the heptacyclic product (dimer B, 28) having a ring structure of similar type to the dimeric quinoline alkaloids (paraensidimerins). The structures of the cyclization products (dimer A, dimer B and dimer C) have been determin ed by spectroscopic and X-ray diffraction methods. Mechanistic pathway s for the chemical synthesis of polycyclic quinolinone products and th eir relevance in the biosynthesis of dimeric quinoline alkaloids are d iscussed.