Bicyclic β-Hydroxytetrahydrofurans as Precursors of Medium Ring Keto-Lactones
摘要:
The reaction of a series of cis-fused bicyclic beta-hydroxytetrahydrofurans with ruthenium tetraoxide, generated in situ from ruthenium trichloride and sodium periodate, afforded 9- and 10-membered keto-lactones in moderate to good yields, in a clean and straightforward fashion. The starting beta-hydroxyethers were obtained from the corresponding 3-alkenols by two alternative procedures, depending on their pattern of substitution: (a) epoxidation by dimethyldioxirane, followed by base-catalyzed cyclization of the resulting epoxyalcohol, and (b) thallium trinitrate-mediated cyclization of the 3-alkenols, a method already described by our group.
Thallium Trinitrate Mediated Oxidation of 3-Alkenols: Ring Contraction vs Cyclization
摘要:
The reaction of a series of six-membered ring 3-alkenols with thallium trinitrate (TTN) in three different experimental conditions was studied. Either cyclization products or ring contraction products were obtained, depending on the structure of the substrate as well as the nature of the solvent. The reaction of a seven-membered ring 3-alkenol with TTN led to the ring contraction product exclusively.
Heterogeneous permanganate oxidations: Synthesis of medium ring keto-lactones via substituent directed oxidative cyclisation
作者:Jagattaran Das、Srinivasan Chandrasekaran
DOI:10.1016/s0040-4020(01)85664-7
日期:1994.1
Homoallyl alcohols 4a-b and 5a-b undergo smooth oxidative cyclisation to give the corresponding ring enlarged keto-lactones under heterogeneouspermanganateoxidation conditions.
allows achieving superior degrees of regioselectivity and yields in the desaturation of alcohols compared to those obtained by the state-of-the-art desaturation methods. The HAT at unactivated C(sp3)-H sites is enabled by the easily installable/removable Si-auxiliaries. Formation of the key hybrid alkyl Pd-radical intermediates is efficiently induced by visible light from alkyl iodides and Pd(0) complexes
已经开发了一种通用的、有效的和位点选择性的可见光诱导的 Pd 催化的脂肪醇远程去饱和成有价值的烯丙基、高烯丙基和双高烯丙基醇。这种转变通过混合 Pd 自由基机制进行,该机制协同结合了自由基方法的有利特征,例如简便的远程 CH HAT 步骤,与过渡金属催化化学(选择性β-氢消除步骤)的特征。与通过最先进的去饱和方法获得的那些相比,这允许在醇的去饱和中实现更高程度的区域选择性和收率。未激活的 C(sp3)-H 站点的 HAT 由易于安装/可拆卸的 Si 助剂启用。烷基碘化物和 Pd(0) 配合物的可见光可有效诱导关键杂化烷基 Pd-自由基中间体的形成。值得注意的是,该方法不需要外源性光敏剂或外部氧化剂。
Rhodium(I)-Catalyzed Decarbonylative Spirocyclization through CC Bond Cleavage of Benzocyclobutenones: An Efficient Approach to Functionalized Spirocycles
作者:Tao Xu、Nikolas A. Savage、Guangbin Dong
DOI:10.1002/anie.201310149
日期:2014.2.10
The rhodium‐catalyzed formation of all‐carbon spirocenters involves a decarbonylative coupling of trisubstituted cyclic olefins and benzocyclobutenones through CC activation. The metal–ligand combination [Rh(CO)2Cl}2]/P(C6F5)3 catalyzed this transformation most efficiently. A range of diverse spirocycles were synthesized in good to excellent yields and many sensitive functional groups were tolerated
Deconstructive Asymmetric Total Synthesis of Morphine‐Family Alkaloid (−)‐Thebainone A
作者:Si‐Hua Hou、Adriana Y. Prichina、Guangbin Dong
DOI:10.1002/anie.202103553
日期:2021.6
deconstructive strategy for the first asymmetric synthesis of (−)-thebainone A, capitalizing on an enantioselective C−C bond activation and a C−O bond cleavage reaction. The rhodium-catalyzed asymmetric “cut-and-sew” transformation between sterically hindered trisubstituted alkenes and benzocyclobutenones allowed efficient construction of the fused A/B/C rings and the quaternary center of the natural
在此,我们描述了首次不对称合成 (−)-蒂巴因酮 A 的解构策略的开发,利用对映选择性 C−C 键激活和 C−O 键裂解反应。铑催化的空间位阻三取代烯烃和苯并环丁烯酮之间的不对称“剪切和缝合”转化允许有效构建稠合的A/B/C环和天然产物的四元中心。新优化的条件显示出广泛的底物范围和出色的对映选择性(高达 99.5:0.5 er)。利用硼介导的醚键断裂,我们通过两条互补路线完成了吗啡生物碱(−)-蒂巴因酮A的合成。
Beyond the Corey Reaction: One-Step Diolefination of Cyclic Ketones
作者:Ekaterina D. Butova、Andrey A. Fokin、Peter R. Schreiner
DOI:10.1021/jo070653z
日期:2007.7.1
reaction the Yurchenko diolefination). Our mechanistic proposal involves the deprotonation of the betaine that forms after the attack of dimethylsulfoxonium methylide on the carbonyl group of the ketone. The key step of the diolefination reaction involves a [2,3]-sigmatropic rearrangement of the ylide to a γ-unsaturated sulfoxide with a barrier of 9.9 kcal/mol (ΔH298, MP2/cc-pVDZ, for the cycloheptane