Gold and Carbene Relay Catalytic Enantioselective Cycloisomerization/Cyclization Reactions of Ynamides and Enals

The combined use of gold as transition metal catalyst and N‐heterocyclic carbene (NHC) as organic catalyst in the same solution for relay catalytic reactions was disclosed. The ynamide substrate was activated by gold catalyst to form unsaturated ketimine intermediate that subsequently reacted with the enals (via azolium enolate intermediate generated with NHC) effectively to form bicyclic lactam products with excellent diastereo‐ and enantio‐selectivities. The gold and NHC coordination and dissociation can be dynamic and tunable events, and thus allow the co‐existence of both active metal and carbene organic catalysts in appreciable concentrations, for the dual catalytic reaction to proceed.     

炔醇分子内环化促发的串联反应在螺杂环化合物合成中的应用

螺杂环化合物独特的立体结构和丰富的理化特性,激发了研究工作者对其高效合成方法的持续关注.炔醇在过渡金属作用下经exo-dig式分子内环化可原位形成环外烯醇醚,其作为一类高活性的C2合成子,能够与同时具有亲电和亲核特性的“双亲性底物”发生串联反应,实现螺杂环骨架的快速构建.综述了近年来炔醇分子内环化促发的串联反应在螺杂环...     

New Reactions of Ortho Esters

Russian Journal of Organic Chemistry - A new reaction of triethyl orthoformate with ethyl butyrate has been revealed. It afforded diethoxymethyl butanoate and its hydrated form,...     

Cobalt-Catalyzed Reactions of Propargylamines with Elemental Sulfur

Russian Journal of Organic Chemistry - Substituted thioamides, thiophenes, thiiranethiones, and thietethiones have been synthesized by reactions of propargylamines with elemental sulfur in the...     

Nucleophilic Displacement Reactions on Phosphoric Esters and Amides by Lithium Reagents. A Powerful Tool in Organic Synthesis

Abstract

Alkylation of phoshoric esters and amides by lithium reagents represents a new rouge to α-lithioalkylphosphonates. converssion of which leads to phosphoryl stabilized anions of synthetic use.     

Hydrogen-Bond Cyclization Programming of Ultrasensitive Esters and Its Application in Gene Delivery

The ester bond as a universal linker has recently been applied in gene delivery systems owing to its efficient gene release by electrostatic repulsion after its cleavage. However, the ester bond is nonlabile and is difficult to cleave in cells. This work reports a method in which a secondary amine was introduced to the β-position of the ester bond to generate a hydrogen-bond cyclization (HBC) structure that can make the ester bond hydrolysis ultrafast. A series of molecules comprising ultrasensitive esters that can be activated by H₂O₂ were synthesized, and it was found that those able to form an HBC structure showed complete ester hydrolysis within 5 h in both water and phosphate-buffered saline solution, which was several times faster than other methods reported. Then, a series of amphiphilic poly(amidoamine) dendrimers were constructed, comprising the ultrasensitive ester groups for gene delivery; it was found that they could effectively release genes under quite a low concentration of H₂O₂ (<200 μm ) and transport them into the nucleus within 2 h in Hela cells with high safety. Their gene transfection efficiencies were higher than that of PEI_25k. The results demonstrated that the hydrogen-bond-induced ultrasensitive esters could be powerfully applied to construct gene delivery systems.     

Direct Synthesis of Adipic Esters and Adiponitrile via Photoassisted Cobalt-Catalyzed Alkene Hydrodimerization

The direct hydrodimerization of acrylates and acrylonitrile offers a general streamlined access to industrially important intermediates to nylon 6,6. However, a practical catalytic method for this process has thus far underdeveloped owing to the challenges in regioselectivity and environmental compatibility of applied reagents. Here, we report a cobalt-catalyzed tail-to-tail hydrodimerization of activated alkenes driven by a visible-light photoredox catalysis at ambient temperature, which is applicable to both adipates and adiponitrile synthesis from potentially renewable feedstocks. This protocol utilizes half equivalent of hantzsch ester as a recyclable two-electron and two-proton donor with the assistance of catalytic amount of base as a proton shuttle, and has been shown to be highly regioselective and efficient for hydrodimerizing various activated alkenes to 1,4-difunctionalized butane derivatives.     

Kinetics-Based Approach to Developing Electrocatalytic Variants of Slow Oxidations: Application to Hydride Abstraction-Initiated Cyclization Reactions

Electrochemical oxidant regeneration is challenging in reactions that have a slow redox step because the steady-state concentration of the reduced oxidant is low, causing difficulties in maintaining sufficient current or preventing potential spikes. This work shows that applying an understanding of the relationship between intermediate cation stability, oxidant strength, overpotential, and concentration on reaction kinetics delivers a method for electrochemical oxoammonium ion regeneration in hydride abstraction-initiated cyclization reactions, resulting in the development of an electrocatalytic variant of a process that has a high oxidation transition state free energy. This approach should be applicable to expanding the scope of electrocatalysis to include additional slow redox processes.     

有机膦催化环化及环加成反应在天然产物全合成中的应用研究进展*

有机膦小分子催化是一种反应条件温和、环境友好的有机合成方法,已广泛应用于有机合成领域。其中亲核有机膦催化的环化及环加成反应已经逐渐发展成为构建碳环和杂环化合物以及天然产物的重要工具之一。通过介绍近年来发展的有机膦催化环化及环加成反应的方法学,综述了近年来有机膦催化的环化及环加成反应在天然产物全合成中的应用研究进展。     

通过自由基串联环化反应合成4-喹诺酮类化合物

4-喹诺酮结构广泛存在于天然产物和药物分子中. 本工作以易得的N-芳基-O-炔丙基氨基甲酸酯为原料, CO为羰基源, 发展了一种高效、模块化合成4-喹诺酮结构的方法. 氨基甲酸酯底物经2-碘酰基苯甲酸(IBX)氧化产生酰胺氮自由基, 进而发生自由基串联环化反应得到4-喹诺酮结构.     

Cobalt-Catalyzed Enantioselective Ring-Opening Reactions of Oxa- and Aza-bicyclic Alkenes with Alkenylboronic Acids

Catalytic enantioselective ring-opening of oxa-and aza-bicyclic alkenes with readily available accessible alkenylboronic acids,promoted by a chiral phosphine-Co complex,is reported.Such a process represents the unprecedented Co-catalyzed introduction of various alkenyl groups onto the oxa-and aza-bicyclic alkenes,affording a wide range of multisubstituted functionalized cyclohexenes in up to 98%yield and 99.5:0.5 er.     

可见光诱导烯烃串联加成环化合成多氟烷基化异喹啉二酮

发展了一种可见光诱导的活泼烯烃与全氟碘代烷串联加成环化合成多氟异喹啉二酮的反应。 在可见光诱导下,多种N-丙烯酰基-N-丁基苯甲酰胺衍生物与全氟碘代烷发生自由基串联加成环化反应,以54%~80%的产率合成了一系列的多氟取代异喹啉二酮衍生物。 为具有潜在药用价值的多氟取代异喹啉二酮合成提供了一条高效、条件温和、绿色的新途径。     

Total Synthesis of Ascospiroketal A Through a AgI‐Promoted Cyclization Cascade

The total synthesis of four candidate stereostructures for the marine octaketide ascospiroketal A have been achieved. These concise and highly stereocontrolled syntheses feature a unique Ag^I‐promoted cyclization cascade involving an oxetanyl ketochlorohydrin to access the entire tricyclic core of the natural product in one step. These syntheses also establish the full stereochemistry for the ascospiroketal natural products.     

Cobalt-Catalyzed Cyclization of 2-Bromobenzamides with Carbodiimides: A New Route for the Synthesis of 3-(Imino)isoindolin-1-ones

A novel synthetic pathway to approach 3-(imino)isoindolin-1-ones by the Co-catalyzed cyclization reaction of 2-bromobenzamides with carbodiimides has been developed. This catalytic reaction can tolerate a variety of substituents and provide corresponding products in moderate yields for most cases. According to the literature, the reaction mechanism is proposed through the formation of a five-membered aza-cobalacycle complex, which carries out the following reaction subsequence, including nucleophilic addition and substitution, to furnish the desired structures.     

Access to Indole-Fused Benzannulated Medium-Sized Rings through a Gold(I)-Catalyzed Cascade Cyclization of Azido-Alkynes

Because benzannulated and indole-fused medium-sized rings are found in many bioactive compounds, combining these fragments might lead to unexplored areas of biologically relevant and uncovered chemical space. Herein is shown that α-imino gold carbene chemistry can play an important role in solving the difficulty in the formation of medium-sized rings. Namely, phenylene-tethered azido-alkynes undergo arylative cyclization through the formation of a gold carbene intermediate to afford benzannulated indole-fused medium-sized tetracycles. The reactions allow a range of different aryl substitution patterns and efficient access to these otherwise difficult-to-obtain medium-sized rings. This study also demonstrates the feasibility of the semihollow-shaped C-dtbm ligand for the construction of a nine-membered ring.