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Published on: February 7, 2019
Total synthesis of (+)-chinensiolide B via tandem allylboration/lactonization
1Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada.
Abstract:
The chinensiolides are a family of guaiane type alpha-methylene gamma-lactone natural products recently isolated from Ixeris chinensis Nakai, a plant used in Chinese folk medicine. The first enantioselective total synthesis of (+)-chinensiolide B was accomplished in 15 steps for the longest linear sequence with an overall yield of 6.7% starting from inexpensive and readily available (R)-carvone. A highly stereoselective and E/Z-selective tandem allylboration/lactonization reaction between two highly functionalized partners was exploited as a key step. The synthesis also highlights several solutions to chemoselectivity issues arising from the reactive alpha-methylene gamma-lactone. For instance, a ring-closing metathesis formed the requisite seven-membered ring in a chemoselective fashion while avoiding the reactivity of the conjugated alpha-methylene unit.
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