Organic Letters
Letter
conducted under BiCl3 at 80 °C after several trials, such a
transformation was manifested smoothly. Further treatment of
reaction mixture of 34a and 34b with sodium borohydride in
isopropyl alcohol resulted in complete conversion into the
pentacyclic core 9 with a thermodynamically stable cis- fused
5/6 ring system as the EF bicycle in andilesin C. The structure
of 9 was confirmed unambiguously through single-crystal X-ray
crystallography. Interestingly, we could not detect any amount
of compound 9′ during the reaction process. In a following
experiment, compound 34a was purified and isolated from the
reaction mixture and then treated with NaBH4/iPrOH. The
reaction also directly afforded compound 9 without other
intermediates including 9′ being detectable, indicating that
isomerization of the stereogenic center adjacent to the ester in
34a should be very facile and fast either through formation of
9′ or not.
diffraction work. We are grateful to Dr. Daibing Luo at Sichuan
University for his help with single-crystal analysis.
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In conclusion, we have completed the core pentacyclic
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ASSOCIATED CONTENT
* Supporting Information
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Accession Codes
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AUTHOR INFORMATION
Corresponding Authors
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ORCID
Notes
(19) Taber, D. F.; Herr, R. J.; Pack, S. K.; Geremia, J. M. J. Org.
Chem. 1996, 61, 2908.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge financial support from the NSFC
(21672153), the Open Fund of State Key Laboratory of
Natural Medicines in China Pharmaceutical University
(SKLNMKF201810), and the Fundamental Research Funds
for the Central Universities. We thank the Analytical & Testing
Center of Sichuan University for NMR recording and X-ray
D
Org. Lett. XXXX, XXX, XXX−XXX