which, however, becomes flatter and flatter on passing from (1a) to (1e). As a result there is a progessive lessening of steric hindrance on the syn face which neatly parallels the observed increase in syn attack along the series (1a–e). Moreover the energy required to remove steric hindrance on passing from the boat-like to the half-planar conformation is definitively lower for (1c–e) than for (1b and
The photocyclization of cis,cis-Cyclohepta-1,3-diene (1) to give bicyclo[3.2.0]hept-6-ene (2) proceed through a two-step process, in which the cis,cis-isomer (1) isomerizes photochemically to the highly strained cis,trans-cycloheptadiene (5) which in turn cyclizes thermally to give the bicycloheptene (2); the cis,trans-isomer (5) was trapped chemically by acidic methanol at room temperature to give
Studies on the Pauson–Khand reaction of alkynyl sulfoxides. Unexpectedly easy racemization of their dicobalt hexacarbonyl complexes
作者:Elvira Montenegro、Albert Moyano、Miquel A Pericàs、Antoni Riera、Angel Alvarez-Larena、Joan-F Piniella
DOI:10.1016/s0957-4166(99)00032-4
日期:1999.2
afford 1,3-rearranged enantiomerically enriched α-butyl and α-phenyl enones. The absolute configuration of the Pauson–Khand adducts was determined by X-ray diffraction. The decreased enantiomeric excess of the final products uncovered an unprecedented low temperature racemization of the hexacarbonyldicobalt complexes of alkynyl sulfoxides.
First formation of 1,1-dihalo-1,3-butadienes from reactions of dichloro- and dibromocarbenes with cyclopropenes via new addition-rearrangements
作者:Jürgen Weber、Linxiao Xu、Udo H. Brinker
DOI:10.1016/s0040-4039(00)61306-0
日期:1992.8
dichloro-, dibromo-, and bromofluorocarbene, 2,3-diaryl-1,1-dihalo-1,3-butadienes are formed. In addition, 1,3-diaryl-2,3-dihalocyclo-1-butenes are formed. For the formation of the 1,1-dihalobutadienes, new addition-rearrangement mechanisms are proposed. Furthermore, some reactions of cyclobutenes with dihalocarbenes are described.
Cyclobutene photochemistry. Nonstereospecific photochemical ring opening of simple cyclobutenes
作者:K. Brady Clark、William J. Leigh
DOI:10.1021/ja00254a030
日期:1987.9
The photochemistry of bicyclo(3.2.0)hept-6-ene, bicyclo(4.2.0)oct-7-ene, and cis- and trans-3,4-dimethylcyclobutene has been investigated in hydrocarbon solution with monochromatic far-ultraviolet (185 and 193 nm) light sources. All of these simple cyclobutene derivatives undergo ring opening to yield the isomeric 1,3-dienes, and the latter three open nonstereospecifically to yield mixtures of the
研究了双环(3.2.0)庚-6-烯、双环(4.2.0)辛-7-烯和顺式和反式-3,4-二甲基环丁烯在具有单色远紫外光的烃溶液中的光化学( 185 和 193 nm) 光源。所有这些简单的环丁烯衍生物都进行开环以产生异构的 1,3-二烯,后三种以非立体有择的方式打开以产生可能的几何异构体的混合物。异构的 3,4-二甲基环丁烯产生三种 2,4-己二烯异构体的不同混合物,并且在每种情况下,混合物被加权以有利于轨道对称性禁止异构体。已尝试在纯反旋转的背景下分析双环 (4.2.0) 辛烯和异构 3,4-二甲基环丁烯开环的相对异构二烯产率,最近的 ab initio 计算表明的绝热开环机制应该是可能的。虽然前一种化合物的结果与这种机制一致,但对后两种化合物光解产生的异构 2,4-己二烯的相对产率的分析表明,通过正式禁止的旋转途径进行的光化学开环可能在一定程度上竞争具有旋转环开口。