Simple Designs for the Construction of Complex Trans-Fused Polyether Toxin Frameworks. A Linear Strategy Based on Entropically Favored Oxirane Ring Enlargement in Epoxycycloalkenes Followed by Carbon-Carbon or Carbon-Oxygen Bond-Forming Cyclizations

Article abstract of DOI:10.1021/jo00089a034

A successful design for the construction of trans-fused medium-size cyclic ethers is described.The key features of the synthesis are as follows: (i) intramolecular oxirane ring expansion in cycloalkenes to give bridged oxabicyclic systems and (ii) linear, one- or two-directional synthetic operations which generate external oxocycles in single reaction steps.The general approach involves the intramolecular addition of a stable γ-alkoxy-substituted allylstannane to an aldehyde carbonyl group, and the entire reaction is conducted in a one-pot process which includes the following: (i) vic-diol fragmentation from the bridged oxabicyclic precursor and (ii) Lewis acid-induced cyclization of the resulting aldehyde-allylic tin system.While the present strategy was mostly developed around racemic models, the potential for adoption of enantioselective features is immediate.The versatility, scope, limitations, and potential applications of the present technology are discussed in detail.