Organic Syntheses Using Recyclable Organocobalt Complexes as a Controller

(1)肟醚的电化学自由基环化：我们建立了有机钴络合物在整体电池体系中的牺牲阳极电还原新工艺，并考察了钴肟催化的肟醚自由基环化反应。溴代肟醚的环化反应进行得很干净，得到了氨基醇衍生物。伯溴化物、仲溴化物和叔溴化物分别作为用肟基捕获相应自由基的结果而导致环化产物。环状产物的立体化学与起始酮醚的几何构型无关。碳-氮双键反应生成环戊烷结构。(2)连续自由基环化和与醛的偶联反应。用电化学生成的低价钴络合物研究了溴炔与醛的分子间自由基偶联反应。该偶联产物的形成可以用自由基环化生成的乙烯基自由基与苯甲醛的烷基自由基偶联来解释。(3)烯基和烷基钴配合物的制备及其反应活性。以36%的得率提供了乙烯基钴肟。根据IR和核磁共振数据，乙烯基钴肟的C=C双键与钴原子共轭，Bence对1，3-偶极加成和Diels-Alder反应反应较弱。此外，还研究了活性更强的烯基钴配合物的合成。或者，通过钴-氢化物络合物与丙烯酸酯的加成反应制备烷基钴络合物。产物的酯基也与钴原子共轭。看来，氯磺酰异氰酸酯等高度缺电子的化合物可以进行反电子需求环加成反应。

(1)Electrochemical Radical Cyclization of Oxime Ethers.We have developed a new procedure for electroreduction with organocobalt complex by using a sacrificial anode in an undivided cell system and examined the cobaloxime-mediated radical cyclization of the oxime ethers. The cyclization of the bromo oxime ethers proceeded cleanly to give the amino alcohol derivatives. The primary, secondary, and tertiary bromides led to the cyclization products as a results of trapping of the corresponding radicals with the oxime function, respectively. The stereochemistry of the cyclic products is independent of the geometry of the starting oxime ethers. Carbon-nitrogen double bond was found to be reactive for formation of cyclopentane structures.(2)Successive Radical Cyclization and Coupling Reaction with Aldehyde.Intermolecular radical coupling of bromo alkynes with aldehyde was examined by using the electrochemically generated low valency coblat complex. The formation of the coupling product can be explained by the coupling of the vinyl radical, produced as a result of radical cyclization, with keyl radical from benzaldehyde.(3)Preparation of Alkenyl-and Alkyl-cobalt Complexes and Their Reactivities.The reaction of chloropyridinecobaloxime with vinylmagnesium bromide (4 equiv.) afforded the vinylcobaloxime in 36% yields. The C=C double bond of the vinylcobaloxime are conjugated with the cobalt atom according to the IR and NMR data, and bence are less reactive toward the 1,3-dipolar addition and Diels-Alder reaction. Syntheses of more reactive alkenyl-cobalt complexes were also studied. Alternatively, the alkyl-cobalt complexes were prepared by the addition reaction of cobalt-hydride complex to acrylates. The ester group of the product is also conjugated with the cobalt atom. It seems that highly electron deficient compounds such as chlorosulfonylisocyanate are amenable to the reverse-electron demand cycloaddition.