二碘化钐作用下缺电子烯烃的还原偶联反应

室温下SmI2-HMPA-t-BuOH-THF体系能顺利地将丁烯二酸二酯还原偶联为1, 2, 3, 4-四烷氧基羰基丁烷, 同样条件下, 亚苄基氰乙酸乙酯,α-乙氧羰基肉桂酸乙酯, α-乙酰基肉桂酸乙酯和亚苄基丙二酸亚异丙酯等化合物也发生还原偶联反应得到相应的二聚体。     

Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

Reactions proceeding through open-shell, single-electron pathways offer attractive alternative outcomes to those proceeding through closed-shell, two-electron mechanisms. In this context, samarium diiodide (SmI(2) ) has emerged as one of the most important and convenient-to-use electron-transfer reagents available in the laboratory. Recently, significant progress has been made in the reductive chemistry of other divalent lanthanides which for many years had been considered too reactive to be of value to synthetic chemists. Herein, we illustrate how new samarium(II) complexes and nonclassical lanthanide(II) reagents are changing the landscape of modern reductive chemistry.     

Sm(II)-Mediated Reduction in Water: Importance of the Additive in the Proportionation of SmCl3 and Sm

Mechanistic studies of the SmCl₃-Sm system in water were carried out. The addition of N,N-dimethylacetoamide (DMA) enhanced the reactivity of the one-electron reduction. According to the ultraviolet–visible (UV-vis) analysis, DMA was found to accelerate proportionation of SmCl₃ and Sm.     

Chemoselective Reduction of Some Condensates derived from Chromone-3-carbaldehyde using Sm and Zn

Condensates 4–6 undergo reductive dimerization with Sm in THF containing aqueous NH₄Cl to produce 7–9, whereas with Zn under similar reaction condition 3–5 produce 10–12.     

活性钛与芳基丙酮的还原偶合反应

羰基化合物还原偶合是形成碳-碳键的一种重要方法。本文首次发现此类反应的产物不仅与反应物本身的结构和还原试剂体系有关，还与操作次序有很大关系，且在活性钛表面反应。     

H2 Activation by Non-Transition-Metal Systems: Hydrogenation of Aldimines and Ketimines with LiN(SiMe3)2

In recent years, H₂ activation at non-transition-metal centers has met with increasing attention. Here, a system in which H₂ is activated and transferred to aldimines and ketimines using substoichiometric amounts of lithium bis(trimethylsilyl)amide is reported. Notably, the reaction tolerates the presence of acidic protons in the α-position. Mechanistic investigations indicated that the reaction proceeds via a lithium hydride intermediate as the actual reductant.     

Cobalt- and nickel-catalyzed regio- and stereoselective reductive coupling of alkynes, allenes, and alkenes with alkenes

Transition-metal-catalyzed coupling of two different C-C pi components through a metallacycle intermediate is a highly atom economical method to construct C-C bonds in organic synthesis. The metal-catalyzed coupling of an alkene and alkyne generally gives an Alder-ene or reductive coupling product. In this article, we focus on the cobalt- and nickel-catalyzed reductive coupling of alkynes, allenes, and alkenes with alkenes. These reductive coupling reactions provide convenient methods for the synthesis of various alkenes, dienes, functionalized alkanes, lactones, lactams, and cyclic alcohols in a highly regio- and stereoselective manner. A chemselective formation of metallacyclopentene intermediate from the two different C-C pi components and a low-valence metal species plays a key role for the high regio- and stereoselectivity of the catalytic reaction.     

Nickel-catalyzed reductive cyclizations and couplings

For over 50 years, nickel catalysis has been applied in cycloaddition processes. Nickel-catalyzed reductive couplings and cyclizations, however, have only recently attracted a high level of interest. This group of new reactions allows a broad range of multicomponent couplings involving two or more pi components with a main-group or transition-metal reagent. These processes allow the assembly of important organic substructures from widely available reaction components. Multiple contiguous stereocenters, polycyclic ring systems, and novel arrays of complex functionality may often be prepared from simple, achiral, acyclic precursors. With three or more reactive functional groups participating in the catalytic processes, many mechanistic questions abound, including the precise timing of bond constructions and the nature of reactive intermediates. This Review is thus aimed at providing a critical evaluation of recent progress in this rapidly developing field.     

Preparation of polymeric alcohol bearing oligo(oxyethylene) moiety by radical polyaddition through ketyl radical

Hydrophilic polymers having both oligo(oxyethylene) moieties and tertiary alcohol units in the main chain were prepared by the radical polyaddition of the dike-tones with distyryl compounds by using samarium(II) iodide as an electron transfer agent. Polyaddition of 4,4′-(1,4-phenylene)bis-2-butanone or 6,9-dioxatetradeca-2,13-dione with distyryl compounds such as 1,15-di(4-ethenylphenyl)-2,5,8,11,14-pentaoxapentadecane, 1,18-di(4-ethenylphenyl)-2,5,8,11,14,17-hexaoxaoctadecane, or 1,21-di(4-ethenylphenyl)-2,5,8,11,14,17,20-heptaoxaheneicosane resulted in the formation of the corresponding polymeric alcohols in moderate yields (46–75%). The produced polymers showed high solubility in common solvents, and their molecular weights estimated by GPC (THF, polystyrene standard) were 5200–8100. No serious difference in the molecular weight of the polymer between after and before the treatment with cerium ammonium nitrate indicated that the produced polymers were inert under the oxidative condition where oxidative cleavage of the main chain of poly(vinyl alcohol) takes place. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 715–720, 1997     

Low-valent titanium induced reductive cyclization of nitro compounds and aliphatic ketones:facile synthesis of 3,4-dihydro-(2H) -1,2,4-benzothiadiazine-1,1-dioxides

The intermolecular reductive cyclization of o-nitrobenzene-sulfonamides with aliphatic ketones induced by TiCl4/Sm system was studied and a series of 3,3-disubstituted-3,4-dihydro-(2H)-1,2,4-benzothiadiazine-1,1-dioxides were synthesized in moderate to high yields under mild and neutral conditions.     

低价钛引起的酰氯与脂肪酮的还原偶联反应

在低价钛(TiCl4-Zn)试剂作用下, 酰氯与两分子脂肪酮发生分子间交叉还原偶联反应生成烯烃3。     

Intermolecular reductive coupling of hindered N-aryl imines towards the modular synthesis of chiral N-heterocyclic carbenes

We describe a simple method for the synthesis of hindered N-aryl diamines. The diastereoselectivity for these processes are relatively low but the diamines can be separated using either chromatography or selective crystallization. Separation of enantiomers can be accomplished using HPLC equipped with a chiral stationary phase.     

(ArO)2Sm(THF)4催化N-苯基马来酰亚胺聚合

发现二价稀土配合物二 ( 2 ,6 二叔丁基 4 甲基苯氧基 )钐 [(ArO) 2 Sm (THF) 4]能较好地引发N 苯基马来酰亚胺 (N PMI)的聚合 ,溶剂对聚合的影响较大 ,在四氢呋喃中聚合转化率最高 ,且聚合转化率随单体浓度的提高而提高 ,而温度对聚合的影响不大。     

Magnesium(I) dimers as reagents for the reductive coupling of isonitriles and nitriles

The reactivity of two β-diketiminate coordinated magnesium(I) dimers, [LMgMgL], L=[(RNCMe)(2) CH](-) , R=C(6) H(3) iPr(2) -2,6 ((Dip) Nacnac(-) ) or mesityl ((Mes) Nacnac(-) ), towards a series of isonitriles and nitriles have been examined. Reactions with the isonitriles, RN?C: (R=tBu or C(6) H(3) Me(2) -2,6 (Xyl)), led to reductive C?C couplings and the formation of [{((Dip) Nacnac)Mg}(2) {μ-(XylN=C-)(2) }] and [{((Mes) Nacnac)Mg}(2) {μ-(tBuN=C-)(2) }], or a reductive N?C cleavage and the generation of the magnesium cyanide complex, [{((Dip) Nacnac)Mg(μ-CN)}(3) ]. Reactions of the magnesium dimers with benzonitrile, PhC?N, afforded the C?C-coupled products, [((Dip) Nacnac)Mg[μ-{N=C(Ph)-}(2) ]Mg(NCPh)((Dip) Nacnac)], and [{{((Mes) Nacnac)Mg}(2) [μ-{N=C(Ph)-}(2) ]}(2) ], whereas the reductive C?C cleavage of tBuC?N gave rise to a mixture of [((Dip) Nacnac)Mg(tBu)(NCtBu)] and [{((Dip) Nacnac)Mg(μ-CN)}(3) ]. In contrast, a combination of net nitrile isomerization and C?C coupling processes was involved in the reduction of Me(3) SiC?N, which yielded [{((Dip) Nacnac)Mg}(2) {μ-(Me(3) SiN=C-)(2) }]. All new compounds were crystallographically and spectroscopically characterized. The outcomes of the reported reactions were found to be dependent upon both the steric bulk of the magnesium(I) reagent, and the nature of the isonitrile/nitrile substituent. This combined with a high degree of selectivity for the reactions, indicates that magnesium(I) dimers may find use by organic and organometallic chemists as viable alternatives to currently available reducing agents that are utilized for the reduction of unsaturated organic substrates.     

Electrochemical reductive carbon-to-carbon coupling of σ-ethynyl complexes of transition metals

The electrochemical properties of σ-ethynyl complexes of chromium subgroup metals were studied by cyclic voltammetry and preparative-scale electrolysis. The redox cycle of C₅H₅(CO)₃CrC=CPh was shown to give the bis-carbyne complex (η⁵-C₅H₅)(CO)₂Cr≡C-C(Ph)=C(Ph)-C-Cr(CO)₂(η⁵-C₅H₅) formedvia the reductive C_β−C_β coupling of ethynyl moieties. The influence of the nature of the metal atom and the ligand environment on the course of this reaction was considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1955–1958, October, 1998.     

Alkyl formates as reagents for reductive amination of carbonyl compounds

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