二碘化钐作为预催化剂的有机反应

二碘化钐是二价稀土试剂中的代表化合物,在有机合成中用途广泛.综述了近年来催化量二碘化钐促进的有机反应,介绍了二碘化钐作为预催化剂在催化有机反应方面所体现的反应活性及选择性.     

钐试剂在有机合成中的应用

钐试剂在有机合成中的应用是近年来有机合成方法学研究中的热点之一。综述了十余年来本课题组在钐试剂应用于有机合成方面所开展的有关工作：(1)二碘化钐作为偶联剂和还原剂在有机合成中的应用;(2)金属钐直接应用于有机合成;(3)三碘化钐作为路易斯酸应用于有机合成;(4)有机钐试剂在有机合成中的应用。     

催化量SmI3促进的芳烃酰基化反应

自从Kagan将二碘化钐应用于有机合成以来,钐试剂在有机合成中的应用的研究引起了人们的很大兴趣.随着研究的深入,金属钐、二碘化钐、三碘化钐、有机钐等钐试剂在有机合成中的应用越来越广泛[1].我们课题组也研究了三碘化钐促进的一些有机合成反应[2,3].Friedel-Crafts酰基化反应是合成芳酮的重要反应,但在传统的Lewis酸催化的芳烃酰基化反应中,由于络合作用等的影响,存在着催化剂的用量过大、副反应多、选择性差等不足[4].高效、催化量的催化剂的采用是人们期待的目标.本文报道用催化量的(10 mol%)SmI3促进的芳烃酰基化反应,反应方程式如下,产物的结构经IR和1HNMR所确证.     

二碘化钐在有机合成中的应用新进展

综述了2005年以来二碘化钐在有机合成中应用的新进展,主要涉及二碘化钐在还原偶联反应以及作为预催化剂方面的一些新的应用.     

邻-二氨基烯的合成新方法

以芳香醛,硫和胺为起始原料,经Willgerodt—Kindler反应合成硫代酰胺,硫代酰胺在钐／二碘化钐试剂促进下发生脱硫偶联反应,得到邻-二氨基烯类化合物。其结构经1^H NMR,IR,MS和元素分析表征。     

二碘化钐在有机合成中的应用研究

综述了1998年以来二碘化钐在有机合成中的应用研究，主要涉及羰基化合物、 不饱和烃、卤代物、腈及含氧族元素化合物的特殊反应．     

有机转化中二碘化钐及其他钐试剂近期发展研究

钐试剂自被发现以来,一直在有机合成中占据着一席之地.SmI_2优异的单电子转移能力和还原能力都具有重要的研究价值. Sm、allylSmBr、SmI_3等其他钐试剂的潜力也逐渐被开发出来.综述了近5年来SmI_2以及其他钐试剂介入的反应.主要分为三大部分:(1) SmI_2促进的偶联反应研究,(2)其他钐试剂(Sm, allylSmBr, SmI_3, Sm(OTf)_3)等促进的偶联反应研究,(3)钐试剂介入的有机还原反应.     

二碘化钐促进的 β-碲代酯(腈)的合成

本文报道在室温, 中性介质中研究二碘化钐在合成中的应用. 在二碘化钐作用下,二碲醚发生Te-Te键还原断裂, 生成碲负离子物种, 后者再与α,β-不饱和酯(腈)发生Michael加成, 得到β-碲代酯(腈), 产率较高.     

钐试剂在有机合成中的应用

本文综述了钐试剂在有机合成中的应用,包括还原反应,碳-碳键形成反应以及催化作用。     

三碘化钐催化的一锅法合成α-胺基腈化合物

在三碘化钐催化下,羰基化合物(醛、酮)、胺(伯胺、仲胺)和三甲基氰硅烷(TMSCN)能进行Strecker反应,以良好的收率得到相应的α-氰基化合物.在该反应条件下,底物中的官能团(硝基、碳碳双键和卤素等)不受影响.     

Samarium Diiodide Mediated Reactions in Total Synthesis

Introduced by Henri Kagan more than three decades ago, samarium diiodide (SmI₂) has found increasing application in chemical synthesis. This single‐electron reducing agent has been particularly useful in C? C bond formations, including those found in total synthesis endeavors. This Review highlights selected applications of SmI₂ in total synthesis, with special emphasis on novel transformations and mechanistic considerations. The examples discussed are both illustrative of the power of this reagent in the construction of complex molecules and inspirational for the design of synthetic strategies toward such targets, both natural and designed.     

Some uses of mischmetall in organic synthesis

Mischmetall, an alloy of the light lanthanides, has been used in a variety of organic reactions, either as a coreductant in samarium(II)-mediated reactions (Barbier and Grignard-type reactions, pinacolic coupling reactions) or as the promoter of Reformatsky-type reactions. It has been also employed as the starting material for easy syntheses of lanthanide trihalides, the reactivity of which has been explored in Imamoto and Luche–Fukuzawa reactions and in Mukaiyama aldol reactions.     

Mild and Highly Efficient Protocol for the Synthesis of Benzimidazoles Using Samarium Triflate [Sm(OTf)3]

One-pot synthesis of benzimidazole compounds from ortho-phenylenediamine and a variety of aldehydes was developed under mild reaction conditions. All the reactions were carried out in the presence of samarium triflate (10 mol%) in acetonitrile at room temperature.     

Carboncarbon bond formation on solid support. Application of the classical Julia-Lythgoe olefination

Reductive elimination of β-benzoyloxysulfones, obtained via solid-phase organic synthesis, with samarium diiodide in the presence of DMPU favors the formation of trans-alkenes.     

Preparation of samarium(II) iodide: quantitative evaluation of the effect of water, oxygen, and peroxide content, preparative methods, and the activation of samarium metal

Samarium(II) iodide (SmI(2)) is one of the most important reducing agents in organic synthesis. Synthetic chemistry promoted by SmI(2) depends on the efficient and reliable preparation of the reagent. Unfortunately, users can experience difficulties preparing the reagent, and this has prevented realization of the full synthetic potential of SmI(2). To provide synthetic chemists with general and reliable methods for the preparation of SmI(2), a systematic evaluation of the factors involved in its synthesis has been carried out. Our studies confirm that SmI(2) is a user-friendly reagent. Factors such as water, oxygen, and peroxide content in THF have little influence on the synthesis of SmI(2). In addition, the use of specialized glovebox equipment or Schlenk techniques is not required for the preparation of SmI(2). However, our studies suggest that the quality of samarium metal is an important factor and that the use of low quality metal is the main cause of failed preparations of the reagent. Accordingly, we report a straightforward method for activation of "inactive" samarium metal and demonstrate the broad utility of this protocol through the electron transfer reductions of a range of substrates using SmI(2) prepared from otherwise "inactive" metal. An investigation into the stability of SmI(2) solutions and an evaluation of commercially available solutions of the reagent is also reported.     

Regioselective samarium diiodide induced couplings of carbonyl compounds with 1,3-diphenylallene and alkoxyallenes: a new route to 4-hydroxy-1-enol ethers

Since its introduction into synthetic organic chemistry, samarium diiodide has found broad application in a variety of synthetically important transformations. Herein, we describe the first successful intermolecular additions of samarium ketyls to typical allenes such as 1,3-diphenylallene (7), methoxyallene (12) and benzyloxyallene (25). Reaction of different samarium ketyls with 1,3-diphenylallene (7) occurred exclusively at the central carbon atom of the allene to afford products 9 in moderate to good yields. In contrast, reductive coupling of cyclic ketones to methoxyallene (12) regioselectively provided 4-hydroxy-1-enol ethers 13, which derive from addition to the terminal allene carbon atom of 12, in moderate to good yields. Whereas the E/Z selectivity with respect to the enol ether double bond is low, excellent diastereoselectivity has been observed in certain cases with regard to the ring configuration (e.g. compound 13 b). Studies with deuterated tetrahydrofuran and alcohol were performed to gain information about the reaction mechanism of this coupling process, which involves alkenyl radicals. The couplings of samarium ketyls derived from acyclic ketones and aldehydes gave lower yields, and in several cases cyclopentanols 20 are formed as byproducts. Branched acyclic ketones and conformationally more flexible cyclic ketones such as cycloheptanone led to a relatively high amount of cyclopentanol derivatives 20, whose formation involves an intramolecular hydrogen atom transfer through a geometrically favoured six-membered transition state followed by a cyclization step. The samarium diiodide mediated addition of 8 b to benzyloxyallene (25) afforded the expected enol ethers 26, albeit in only low yield. Additionally, spirocyclic compounds 27 and 28 were obtained, which are formed by a cascade reaction involving an addition/cyclization sequence. In the novel coupling process described here methoxyallene (12) serves as an equivalent of acrolein. The 1,4-dioxygenated products obtained contain a masked aldehyde functionality and are therefore valuable building blocks in organic synthesis.