氮杂环卡宾催化氰基乙酸酯与二烯酮双Michael反应:非对映选择性合成多取代环己酮和茚

利用氮杂环卡宾(NHC)独特的Br?nsted碱性催化二烯酮与氰基乙酸酯的双Michael加成反应.在10mol%NHC催化下,二乙烯酮可以与氰基乙酸酯反应,以60%～89%的产率和5∶1～20∶1的dr值得到多取代环己酮.在相同反应条件下,邻苯二烯酮与氰基乙酸酯和丙二腈等反应,以77%～98%的产率和20∶1的dr值得到多取代茚产物.     

氮杂环卡宾催化烯酮与N-酰基偶氮化合物的[4＋2]环加成反应

烯酮的不对称环加成反应是合成手性杂环化合物的高效方法．近来,中国科学院化学研究所叶松等发展了手性氮杂环卡宾（NHC）催化的烯酮的不对称环加成反应新方法,实现了烯酮分别与亚胺、醛及仅肛不饱和酮反应,     

氮杂环卡宾催化下官能化萘并吡喃酮的串联合成

在氮杂环卡宾(NHC)催化下,查尔酮衍生物与α-溴代烯醛经过"Michael加成-Michael加成-内酯化"等串联过程,一步合成了官能化萘并吡喃酮.该方法具有产率高、底物易得和条件温和等优点,为萘并吡喃酮的高效构建和官能化提供了新思路.     

双功能[2.2]对环蕃基氮杂环卡宾催化查尔酮的不对称硼化反应的研究

为了达到无金属催化的不对称硼化反应高选择性的目的,设计并合成了基于[2.2]对环蕃的手性氮杂环卡宾前驱体.应用该双功能的卡宾催化剂实现了商业化的联硼酸频哪醇酯[B_2(pin)_2]对查尔酮的不对称加成反应,得到了高达99%收率和97%对映体选择性的有机硼化合物.研究还发现,水作为添加物在该反应中发挥关键作用.     

由α-氰基二硫缩烯酮制备多取代喹唑啉酮化合物

以α-氰基乙酸甲酯为起始原料,经与二硫化碳、碘甲烷反应先得到α-氰基二硫缩烯酮1,1与苯乙酮2反应得2H-吡喃-2-酮-3-腈化物3,碱诱导下3再与丙二腈经环转化得到多取代邻氨基芳香腈4,4与酮5在氢氧化钠催化下环化得到多取代喹唑啉酮目标物6.这组连续转化合成多取代喹唑啉酮的反应具有原料简便、反应温和等优点.     

氮杂环卡宾催化α,β-不饱和酰氯与亚硝基化合物的[4+2]环化反应

报道氮杂环卡宾催化的α,β-不饱和酰氯与亚硝基化合物的形式[4+2]环化反应合成氮杂-δ-内酯([1,2]嗪-6-酮)化合物.反应机理推测可能是卡宾进攻现场生成的烯基烯酮,得到烯基烯醇负离子,然后与取代的亚硝基苯发生[4+2]环合反应,从而得到的氮杂-δ-内酯产物.     

铜-手性氮杂环卡宾化合物催化的不对称1,4-共轭加成反应

近年来,利用金属-手性氮杂环卡宾(NHC)化合物进行不对称催化反应已取得了快速发展.相关报道越来越多,一些反应已获得良好的对映异构体选择性,这显示出金属-NHC化合物在催化合成手性化合物中的潜在用途.按NHC为单齿、双齿配体总结了金属-手性NHC化合物对"α,β-不饱和酮的共轭加成反应的不对称催化,以期对发现高立体选择性金属-NHC催化剂提供一些启发.     

查尔酮参与的不对称Michael加成反应研究进展

综述了近十年来,金鸡纳碱、硫脲、手性离子液体、季铵盐、脯氨酸和葡萄糖类衍生物等有机小分子在催化查尔酮的不对称Michael加成反应中的应用.有机小分子催化的机理大部分都是通过氢键、离子键等与底物相互作用而使其有较好的对映选择性.     

铑和手性螺环磷酸协同催化α-芳基重氮酮对醇的O-H键的不对称插入反应

过渡金属催化卡宾对O-H键的不对称插入反应是合成手性醇及其衍生物的直接方法.近年来,人们发展了多种手性催化剂实现了重氮酯衍生的金属卡宾对醇、酚、羧酸甚至水的O-H键的高对映选择性插入反应,但是重氮酮作为卡宾前体的不对称O-H键插入反应鲜有成功的例子.以非手性双铑络合物和手性螺环磷酸组成的协同催化体系,首次实现了α-重氮酮对醇的O-H键的不对称插入反应,获得了较高的收率和高达95%ee的对映选择性.反应为手性α-烷氧基酮这类重要手性化合物提供了高效的合成方法.还通过密度泛函理论计算,对反应机理进行了初步研究,发现水很可能参与了手性磷酸促进的烯醇中间体质子转移过程.     

氮杂环卡宾催化合成氰基化合物的研究进展

氰基化合物不仅广泛存在于医药和农药分子中,还是一类重要的中间体.传统合成氰基化合物的方法是使用氰化钠、氰化钾和氢氰酸等最简单的氰化试剂,但这类氰化试剂的剧毒性和不稳定性限制了其在合成中的应用.因此发展有机氰化试剂和无氰源试剂构建氰基化合物的策略备受关注.氮杂环卡宾是一类高效的有机小分子催化剂,可用于实现多种碳-碳(C—C)和碳-杂(C—X)键的形成.综述了氮杂环卡宾催化有机氰化试剂和无氰源试剂构建氰基化合物的反应,目的是引起更多的化学工作者关注该领域的发展,并提供氮杂环卡宾催化活化模式的新思路.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.