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The second-generation enantioselective synthesis of heliannuol A and the first enantioselective total synthesis of heliannuol K (via two routes) have both been accomplished efficiently; (heliannuol A, nine steps and 25% yield; heliannuol K, seven steps and 47% yield). Highlights of our synthetic strategy include a substrate-controlled chirality transfer in the Lewis acid mediated Claisen rearrangement of the allyl aryl ether for the key construction of a tertiary stereogenic center at the benzylic position followed by, for heliannuol A, ring-closing metathesis, diastereoselective epoxidation, and regioselective cleavage of the epoxide; and for heliannuol K, ring-closing metathesis and conjugate reduction of the eight-membered enone. |
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