Synthesis of the A–D Ring System of the Gambieric Acids

The A–D fragment of gambieric acids A and C has been synthesized using an asymmetric Tsuji–Trost allylation reaction to couple the two key segments. The A ring fragment has been prepared by a short and highly efficient route involving diastereoselective Lewis acid mediated alkylation of an acetal. Iterative ring-closing metathesis reactions have been used to construct cyclic ethers and assemble the tricyclic B–D fragment