Base-catalyzed intramolecular condensation of tokinolide B.
The novel pentacyclic compound cyclotokinolide B was obtained from the natural phthalide tokinolide B under basic conditions, via the chemoselective -enol lactone opening followed by a Michael addition of the generated carbanion to the enone and subsequent equilibration. This result confirms that some dimeric phthalides undergo intramolecular cyclizations in basic media.
