Synthetic Applications in Radical/Radical Cationic Cascade Reactions
作者:Heiko Rinderhagen、Jochen Mattay
DOI:10.1002/chem.200304827
日期:2004.2.20
acetylenic side chain. The reactions result in bi- to tetracyclic ring systems via a fragmentation-radical/radical cationic addition reaction pathway with well defined ring juncture. The mode of cyclisation (endo/exo) can be partially controlled by addition of nucleophiles due to the suppression of radical cationic reaction pathways. Quantum chemical calculation of the cyclisation transition states underline
Cycloalkylmethyl radicals. Part 4. Electron spin resonance study of conformational equilibria in cyclohexenylmethyl and 4-alkylcyclohexenylmethyl radicals
作者:John C. Walton
DOI:10.1039/p29860001641
日期:——
half-chair conformation of cyclohex-2-enylmethyl radical were determined by line-shape analysis of the exchange-broadened spectra and found to be: log(kf/s–1)= 12.3 –(5.7 kcal mol–1)/2.3RT and log (kb/s–1)= 12.0 –(5.5 kcal mol–1)/2.3RT. The barrier to rotation about the Ċα–Cβ bond in a cyclohexenylmethyl radical is much less than the barrier in a cyclohexylmethyl radical because the former radical has only
对于环己-2-烯基甲基和4-烷基环己-2-烯基甲基,可以通过esr光谱法观察到准轴向和准赤道构象异构体。类似地,环己-3-烯基甲基自由基的轴向和赤道构象异构体可以通过电离能谱法进行区分。该CH的构象的自由能差2在2-位,-Δ˙组ģ ° 300,被发现是0.17±0.03千卡摩尔-1和在3-位-Δ ģ ° 300 = 0.0±0.1大卡摩尔–1。通过交换增宽光谱的线形分析确定了环己-2-烯基甲基自由基半椅构象的阿伦尼乌斯参数,发现为:log(k f / s –1)= 12.3 –(5.7 kcal mol –1)/2.3 RT和log(k b / s –1)= 12.0 –(5.5 kcal mol –1)/2.3 RT。所述屏障以关于C旋转α -C β在游离基的环己烯基键比环己阻挡少得多的自由基,因为前者自由基只有一个顺上C(5)-axial氢阻碍旋转而后者自由基具有两个顺式对C(3)和C(5)-axial氢。
Ammonium-Directed Olefinic Epoxidation: Kinetic and Mechanistic Insights
作者:Méabh B. Brennan、Timothy D. W. Claridge、Richard G. Compton、Stephen G. Davies、Ai M. Fletcher、Martin C. Henstridge、David S. Hewings、Wataru Kurosawa、James A. Lee、Paul M. Roberts、Anne K. Schoonen、James E. Thomson
DOI:10.1021/jo3010556
日期:2012.9.7
substituent to direct the stereochemicalcourse of the epoxidation reaction is either comparable or superior to that of the analogous hydroxyl substituent. Much slower rates of ring-opening of the intermediate epoxides are observed in cyclopentene-derived and cycloheptene-derived allylic amines as compared with their cyclohexene-derived allylic and homoallylic amine counterparts, allowing for isolation of
A new mechanism for reactions of carbenes and bicyclo[1.1.0]butanes
作者:Linxiao Xu、Thomas Miebach、Udo H. Brinker、William B. Smith
DOI:10.1016/0040-4039(91)80012-u
日期:1991.1
Reactions of tricyclo[4.1.0.02,7]heptane (1) with dihalocarbenes and bromine are reported. A new side bond opening mechanism for reactions of carbenes and bicyclo[1.1.0]butanes is proposed.
intramolecular nitrile oxide [3+2] cycloaddition were prepared from the monoacetal of 2,2-dimethylcyclohexane-1,3-dione (5). The nitrile oxides were then generated under high-dilution conditions. In most cases only oligomers were obtained. The isoxazoline 19, containing a 9-membered ring, was formed from the nitrile oxide 17, and a bis(isoxazoline) 21was isolated from the reaction of the nitro compound 16c.
由 2,2-二甲基环己烷-1,3-二酮 (5) 的单缩醛制备了通过分子内氧化腈 [3+2] 环加成形成紫杉烷 8 元 B 环的几种模型。然后在高稀释条件下生成腈氧化物。在大多数情况下,仅获得低聚物。含有9元环的异恶唑啉19由腈氧化物17形成,并且双(异恶唑啉)21从硝基化合物16c的反应中分离。