Total Synthesis of Rubriflordilactone B

• Published in: Angewandte Chemie International Edition 2016-06, Vol.55 (24), p.6964-6968
• Main Authors: Yang, Peng, Yao, Ming, Li, Jian, Li, Yong, Li, Ang
• Format: Article
• Language: English
• Subjects: arenes; electrocyclization; hydrosilylation; terpenoids; total synthesis
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201601915

Taking advantage of a 6π electrocyclization–aromatization strategy, we accomplished the first and asymmetric total synthesis of rubriflordilactone B, a heptacyclic Schisandraceae bisnortriterpenoid featuring a tetrasubstituted arene moiety. The left‐hand fragment was accessed through a chiral‐pool‐based route, and linked to the right‐hand fragment by a Sonogashira coupling. The cis geometry of the electrocyclization substrates was established by hydrogenation or hydrosilylation of the alkyne. An electrocyclization–aromatization sequence finally built the multisubstituted arene. The hydrosilylation approach was of significant advantage in terms of reaction scale, reproducibility, and intermediate stability. The structure of synthetic rubriflordilactone B was validated by X‐ray crystallographic analysis, and found to be consistent with that reported for the authentic natural product based on an independent X‐ray crystallographic analysis. However, obvious differences in the NMR spectra of the synthetic and authentic samples suggest that the authentic samples subjected to X‐ray crystallography and NMR spectroscopy were two different compounds. Going round in circles: The first total synthesis of rubriflordilactone B, a heptacyclic Schisandraceae bisnortriterpenoid with a tetrasubstituted arene moiety, was accomplished in a highly convergent fashion. A 6π electrocyclization/aromatization process was exploited as a key step.