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
摘要:
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.
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
摘要:
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 C10 cis and trans fused oxane-oxepane subunits
作者:Eleuterio Alvarez、Dácil Zurita、Julio D. Martín
DOI:10.1016/s0040-4039(00)79692-4
日期:1991.5
A newsynthetic process for the construction of cis- and trans-fused oxane-oxepane systems starting from (Z,Z)-cyclodeca-2,7-dien-1-ol is described. The Ti(OiPr)4-catalysed transannular oxirane rig expansion is invoked to explain the chemoselective formation of the 11-oxobicyclo[4.4.1] undecane intermediate.
描述了一种新的合成方法,用于从(Z,Z)-cyclodeca-2,7-dien-1-ol开始构建顺式和反式融合的恶烷-环氧庚烷体系。调用Ti(O i Pr)4催化的跨环环氧乙烷装置扩展来解释11-氧代双环[4.4.1]十一烷中间体的化学选择性形成。
Tricyclic oxonium-directed addition: Regiochemistry and stereochemistry of the electrophilic additions to epoxy cycloalkenols.
作者:Eleuterio Alvarez、Eduardo Manta、Julio D Martin、Matias L Rodriguez、Catalina Ruiz-Perez、Dacil Zurita
DOI:10.1016/s0040-4039(00)87844-2
日期:——
The regio- and stereochemistry of electrophile-promoted transannular ring expansion of cyclo 1,5- and 1,6-epoxyalkenes and cyclo trans-1,5-bisepoxides were studied. The results are rationalized in terms of tricyclic oxonium intermediates showing the directing ability of oxygen substituents in the regio- and stereocontrol observed.