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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 aiso observed for the related analogues N-8 deaza ascididemin (3) and kuanoniamine A (4).
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Lindsay et al. (1997) studied this question.
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