Alkylation reactions of anions derived from 2-benzenesulphonyl tetrahydropyran and their application to spiroketal syntiesis
作者:Steven V. Ley、Barry Lygo、Francine Sternfeld、Anne Wonnacott
DOI:10.1016/s0040-4020(01)87660-2
日期:1986.1
Deprotonation of (1) follwed by alkylation with carbonyl compounds or halides gave cyclic enol ether addition products by spontaneous elimination of benzenesulphinic acid. Interception of the initial addition products with aldehydes by reductive desulphonylation to give alkylated tetrahydropyran derivatives proeeeded in moderate yield using sodium naphthalenide. Several of the cystic enol ether addition products
A range of 1-azaspirocycles, spiroaminals and 1,6-diazaspirocycles has been synthesized, starting from simple and readily accessible furan precursors, using a cascade reaction sequence initiated by singlet oxygen.
All‐in‐one: A new and general one‐pot reaction sequence initiated by singlet oxygen that transforms simple furan substrates into complex nitrogen‐bearing aromaticpolycycles having all the structural features of a number of important natural products (for example, the erythrina alkaloids; see scheme, RB=rose Bengal) is reported. The reaction sequence itself uses mild conditions and has wide functional
singlet‐oxygen‐initiated one‐pot transformation of readily accessible furans into 5‐hydroxy‐1H‐pyrrol‐2(5H)‐ones has been developed. The methodology was extended to the synthesis of other high‐value α,β‐unsaturated γ‐lactams. This useful set of transformations relies not only on the photosensitizing ability of methyleneblue, but also on its redox properties: properties that have until now been virtually ignored
Intramolecular 4 + 3 Cycloadditions. Cycloaddition Reactions of Cyclic Alkoxyallylic and Oxyallylic Cations
作者:Michael Harmata、Saleh Elomari、Charles L. Barnes
DOI:10.1021/ja952740r
日期:1996.1.1
larger amounts of cycloadduct derived from extended (exo) transition states. This has been rationalized on the basis of ring strain in the endo transition states in this series. Cyclodecenyl oxyallylic cations are sickle-shaped and stereoselectively undergo cycloadditionviaextendedtransition states to a furan diene tethered by three carbons. Cyclododecenyl oxyallylic cations behave similarly, although
已经研究了氧烯丙基和烷氧基烯丙基阳离子的分子内 4 + 3 环加成。通过三或四个碳链与呋喃相连的环戊烯氧基烯丙基阳离子通过类似于分子间环加成反应的紧凑(内)过渡态以高立体选择性反应。六至八元氧烯丙基阳离子的反应不同,并产生越来越多的来自扩展(外)过渡态的环加合物。这已经根据本系列中内向过渡态中的环应变进行了合理化。环癸烯氧基烯丙基阳离子呈镰刀形,立体选择性地通过扩展过渡态发生环加成反应,生成由三个碳原子连接的呋喃二烯。环十二碳烯氧基烯丙基阳离子的行为相似,尽管证据表明也形成了少量的 W 型阳离子。环状烷氧基烯丙基砜在用 TiCl4 处理后产生相应的阳离子,后者产生环加合物......