Abstract:
Conversion of tetracyclic quinone 1 to the cytotoxic pentacyclic alkaloid ascididemin (2) in 80% yield is achieved by reaction with paraformaldehyde and ammonium chloride in refluxing acetic acid. High yielding annelations are also observed for the related analogues N-8 deaza ascididemin (3) and kuanoniamine A (4).