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
作者:Eleuterio Alvarez、Maria T. Diaz、Ricardo Perez、Jose L. Ravelo、Alicia Regueiro、Jose A. Vera、Dacil Zurita、Julio D. Martin
DOI:10.1021/jo00089a034
日期:1994.5
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 gamma-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.