季铵盐C—N键断裂构建C—X键的研究进展

胺类种类繁多, 原料易得. 胺类的C—N键键能较大, 一般需要通过活化再进行断裂. 近些年发展了多种氨基的活化方法, 其中把胺类转化为季铵盐的活化方法, 制备容易、存放稳定, 具有一定优势. 最近十年左右, 芳香胺和苄胺衍生的季铵盐通过C—N键断裂、构建各种C—X键的研究取得了巨大的研究进展. 本综述主要论述了最近几年需要和不需要过渡金属催化的季铵盐通过C—N键断裂构建C—X键的反应. 通过C—N键断裂, 季铵盐可以构建C—B键、C—C键、C—N键、C—O键、C—Si键、C—P键、C—S键、C—Se键等, 合成硼酸酯、芳烃、烷烃、醚类、胺类、硅烷、膦、硫醚、二硫化物、硒醚、二硒化物等化合物. 而且, 如果是采用手性苄胺衍生的季铵盐, 还可以得到多种高对映体纯的手性有机化合物; 季铵盐的手性在产物中保持良好, 并且, 对所有反应都发生S_N2型的构型翻转.     

C—H氰烷基化:导向基控制的萘酰亚胺C—H氰烷基化

氰基广泛存在药物活性分子中,且氰基可以很容易转化成酰胺、酯基、醛基以及伯胺等官能团,因此有机分子的氰烷基/甲基化反应得到有机和药学研究者的广泛关注。尽管已有合成策略可以选择性引入氰基,近年来最有效的方法是通过C—H键激活直接与乙腈或取代乙腈发生氰甲基/氰烷基化反应,因其具有高效的原子经济性以及可规避预官能团化等优点。因此,本文详细评述了自由基促进的氰甲基化、光化学催化直接氰甲基化、芳环或杂环脱氢偶联氰甲基化、导向基促进的氰甲基化、本课题组发展的荧光团(Fluorophore C—H)直接氰甲基化反应的研究进展。     

条件下C—O—P键的形成

利用水热反应模拟原始地球的水热环境, 以甘油和磷酸二氢铵为原料, 采用非生物手段合成了sn-甘油-1(3)-磷酸和甘油-2-磷酸2种磷酸酯类物质. 通过此反应, 无机磷进入生物分子形成了在生物体中起重要作用C—O—P键. 研究了反应温度、 反应时间及矿物催化剂对反应的影响. 在蒙脱土的催化下, C—O—P键的产率最大可达到1.15%(摩尔分数).     

P?C‐Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine–Boranes

{Rh(xantphos)}‐based phosphido dimers form by P C activation of xantphos (4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H₂BNMeH]_n from H₃B⋅NMeH₂ and dimeric [H₂BNMe₂]₂ from H₃B⋅NMe₂H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization.     

Iron‐Catalyzed Cα?H Oxidation of Tertiary,Aliphatic Amines to Amides under Mild Conditions

De novo syntheses of amides often generate stoichiometric amounts of waste. Thus, recent progress in the field has focused on precious metal catalyzed, oxidative protocols to generate such functionalities. However, simple tertiary alkyl amines cannot be used as starting materials in these protocols. The research described herein enables the oxidative synthesis of amides from simple, noncyclic tertiary alkyl amines under synthetically useful, mild conditions through a biologically inspired approach: Fe‐catalyzed C_α H functionalization. Mechanistic investigations provide insight into reaction intermediates and allow the development of a mild C_α H cyanation method using the same catalyst system. The protocol was further applied to oxidize the drug Lidocaine, demonstrating the potential utility of the developed chemistry for metabolite synthesis.     

A Straightforward Synthesis of 2‐[1‐Alkyl‐5,6‐bis(alkoxycarbonyl)‐1,2,3,4‐tetrahydro‐2‐oxopyridin‐3‐yl]acetic Acid Derivatives via Domino Michael Addition?Cyclization Reaction

A new and efficient synthesis of 2‐[1‐alkyl‐5,6‐bis(alkoxycarbonyl)‐1,2,3,4‐tetrahydro‐2‐oxopyridin‐3‐yl]acetic acid derivatives by a one‐pot three‐component reaction between primary amine, dialkyl acetylenedicarboxylate, and itaconic anhydride (=3,4‐dihydro‐3‐methylidenefuran‐2,5‐dione) is reported. The reaction was performed without catalyst and under solvent‐free conditions with excellent yields. Notably, the ready availability of the starting materials, and the high level of practicability of the reaction and workup make this approach an attractive complementary method to access to unknown 2‐[1‐alkyl‐5,6‐bis(alkoxycarbonyl)‐1,2,3,4‐tetrahydro‐2‐oxopyridin‐3‐yl]acetic acid derivatives. The structures were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this type of domino Michael addition? cyclization reaction is proposed (Scheme 2).     

Gerührt oder geschüttelt? James‐Bond‐Cocktail

Starting from perfluoroheptane, saturated aqueous potassium carbonate solution, methanol, toluene and suitable dyes, a three‐phasic mixture is prepared initially. After shaking – not only stirring – four layers develop. Addition of pentane changes the sequence of two layers. The layers are added in a new sequence and the way of mixing demonstrates the complexity of multi‐phasic systems.     

C?C Cross‐Coupling Reactions of O6‐Alkyl‐2‐Haloinosine Derivatives and a One‐Pot Cross‐Coupling/O6‐Deprotection Procedure

Reaction conditions for the C? C cross‐coupling of O⁶‐alkyl‐2‐bromo‐ and 2‐chloroinosine derivatives with aryl‐, hetaryl‐, and alkylboronic acids were studied. Optimization experiments with silyl‐protected 2‐bromo‐O⁶‐methylinosine led to the identification of [PdCl₂(dcpf)]/K₃PO₄ in 1,4‐dioxane as the best conditions for these reactions (dcpf=1,1′‐bis(dicyclohexylphosphino)ferrocene). Attempted O⁶‐demethylation, as well as the replacement of the C‐6 methoxy group by amines, was unsuccessful, which led to the consideration of Pd‐cleavable groups such that C? C cross‐coupling and O⁶‐deprotection could be accomplished in a single step. Thus, inosine 2‐chloro‐O⁶‐allylinosine was chosen as the substrate and, after re‐evaluation of the cross‐coupling conditions with 2‐chloro‐O⁶‐methylinosine as a model substrate, one‐step C? C cross‐coupling/deprotection reactions were performed with the O⁶‐allyl analogue. These reactions are the first such examples of a one‐pot procedure for the modification and deprotection of purine nucleosides under C? C cross‐coupling conditions.     

Dense or Porous Packing? Two‐Dimensional Self‐Assembly of Star‐Shaped Mono‐, Bi‐, and Terpyridine Derivatives

The self‐assembly behavior of five star‐shaped pyridyl‐functionalized 1,3,5‐triethynylbenzenes was studied at the interface between an organic solvent and the basal plane of graphite by scanning tunneling microscopy. The mono‐ and bipyridine derivatives self‐assemble in closely packed 2D crystals, whereas the derivative with the more bulky terpyridines crystallizes with porous packing. DFT calculations of a monopyridine derivative on graphene, support the proposed molecular model. The calculations also reveal the formation of hydrogen bonds between the nitrogen atoms and a hydrogen atom of the neighboring central unit, as a small nonzero tunneling current was calculated within this region. The title compounds provide a versatile model system to investigate the role of multivalent steric interactions and hydrogen bonding in molecular monolayers.     

Targeting RNA G‐Quadruplex in SARS‐CoV‐2: A Promising Therapeutic Target for COVID‐19?

The COVID‐19 pandemic caused by SARS‐CoV‐2 has become a global threat. Understanding the underlying mechanisms and developing innovative treatments are extremely urgent. G‐quadruplexes (G4s) are important noncanonical nucleic acid structures with distinct biofunctions. Four putative G4‐forming sequences (PQSs) in the SARS‐CoV‐2 genome were studied. One of them (RG‐1), which locates in the coding sequence region of SARS‐CoV‐2 nucleocapsid phosphoprotein (N), has been verified to form a stable RNA G4 structure in live cells. G4‐specific compounds, such as PDP (pyridostatin derivative), can stabilize RG‐1 G4 and significantly reduce the protein levels of SARS‐CoV‐2 N by inhibiting its translation both in vitro and in vivo. This result is the first evidence that PQSs in SARS‐CoV‐2 can form G4 structures in live cells, and that their biofunctions can be regulated by a G4‐specific stabilizer. This finding will provide new insights into developing novel antiviral drugs against COVID‐19.