An efficient approach to access isolable β-chloroenamines via nucleophilic addition/dehydration of α-chloro N-alkoxylactam with organolithium and Grignardreagents is reported. This approach is amenable to the synthesis of β-chloroenamines by incorporating various C(sp) and C(sp2) units, such as alkyne, aryl, and heteroaryl moieties. The sequential reaction has a broad substrate scope and can be carried
Free-radical ring expansion of fused cyclobutanones: stereospecific construction of 5,7-, 6,7-, 7,7-, 8,7-, and 5,8-cis-fused bicyclic systems
作者:Paul Dowd、Wei Zhang
DOI:10.1021/jo00052a034
日期:1992.12
A new method of appending seven- and eight-membered rings to cycloalkenes is described. Treatment of selected alkene precursors with an omega-bromoalkyl ketene or a keteniminium salt leads to haloalkyl cyclobutanone formation. Tri-n-butyltin hydride promoted ring expansion then yields the annulated product. Since the initial cyclobutanone is cis fused, the final product is also produced stereospecifically with a cis ring fusion.
Synthesis of (+)-brefeldin-A
作者:Andrew J. Carnell、Guy Casy、Gilles Gorins、Arefeh Kompany-Saeid、Ray McCague、Horacio F. Olivo、Stanley M. Roberts、Andrew J. Willetts
DOI:10.1039/p19940003431
日期:——
Two routes to (+)-brefeldin A have been investigated. In one the bicyclic ketone 2 was transformed into the hydroxy lactone 7. Subsequent reduction, opening of the heterocyclic ring and epimerization furnished the aldehyde 13. Further steps towards the natural product from this late stage intermediate 13 were not investigated. in the second route, the readily available hydroxy lactone 17 was converted into the enone 22. Conjugate addition of the requisite cuprate reagent to this enone afforded the 3,4-disubstituted cyclopentanone 24 which was converted into brefeldin-A 29 in five steps.