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.
Model studies directed towards microalga polyether toxins. A stereoselective entry into C8 oxepane subunits
作者:Eleuterio Alvarez、M.Teresa Díaz、Ricardo Pérez、Julio D. Martín
DOI:10.1016/s0040-4039(00)79691-2
日期:1991.5
A new synthetic strategy for the regio and stereospecific synthesis of β-alkoxy-substituted oxepanes involving iodine promoted transannular ringexpansion of 9-oxobicyclo (6.1.0) non-4-en-2-one was studied. Stereocontrolled 1,4-dioxygenation of oxepadienes using single oxygen addition occurs trans to the existing substituents and the resulting endoperoxides were cleanly partially hydrogenated using