Tandem Sulfonylation/Cyclization of Vinyl Azides with Aryldiazonium Tetrafluoroborates and SO2

An efficient and facile strategy for the synthesis of 6-(sulfonylmethyl)phenanthridines and its derivatives has been developed via tandem sulfonylation cyclization of vinyl azides under mild conditions in the absence of any catalysts and additives. The reaction simply utilizes easily accessible and cheap K₂S₂O₅ as the sulfur dioxide source, delivering functionalized phenanthridines in moderate to excellent yields with operational simplicity and gram-scale synthesis, as well as good functional-group tolerance.     

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。     

Synthesis of Phaitanthrin E and Tryptanthrin through Amination/Cyclization Cascade

Phaitanthrin E was biomimetically synthesized from methyl indole‐3‐carboxylate and methyl anthranilate or anthranilic acid using the ester group as an activating group. The reaction proceeds through NCS‐mediated dearomatization/TFA‐catalyzed protonation of indolenine/C(2) amination/Et₃N‐promoted aromatization and cyclization in one‐pot procedure. This method is capable of converting simple biomass materials to phaitanthrin E. The synthesis not only allows assessment of antiproliferative activity, but also affords experimental support for the hypothetical biosynthetic pathway of phaitanthrin E. The resulting phaitanthrin E derivatives were evaluated for in vitro antiproliferative activity against human colorectal cancer cells (DLD‐1). The biogenetic intermediate of phaitanthrin E showed higher antiproliferative activity than the natural product, phaitanthrin E. Furthermore, a concise synthesis of tryptanthrin is also accomplished from indole‐3‐carbaldehyde and methyl anthranilate using the aldehyde group as an activating group.     

Cu-Catalyzed Cascade Cyclization of Ketoxime Acetates and Alkynals Enabling Synthesis of Acylpyrroles

Main observation and conclusion A facile copper-based catalytic system has been developed to enable efficient cyclization of methylketoximes and alkynals.This p...     

Inorganic Bergman Cyclization: An Appeal From Theory

The scope of Bergman cyclization is expanded computationally by exploring the cyclization in inorganic B, N substituted derivative. This substitution has introduced polarity into the transition state, which resulted in dramatic lowering of the activation barrier. Natural charge distribution throughout the reaction profile has ascertained this hypothesis. Single B and N atom substitution at 1 and 6 terminal positions lowers the activation barrier by almost half of the original value which becomes even lower in the complete B, N analogue. The parent Bergman and single B, N substituted products were characterized by significant biradical character while the complete B, N substituted analogue was characterized by significant zwitterionic character. Reduction in electron delocalization is also observed in the complete B, N substituted analogue.     

Asymmetric Syntheses of 8-Oxabicyclo[3,2,1]octanes: A Cationic Cascade Cyclization

High octane: A novel and practical syntheses of 8-oxabicyclo[3.2.1]octanes using a cationic cascade cyclization reaction has been developed (see scheme; TIPS=triisopropylsilyl). The diastereomer of the cyclization product isolated depends upon whether the acetal or aldehyde substrate is used.     

可见光诱导的1,n-烯炔的自由基串联环化反应研究进展

碳氮杂环化合物广泛存在于天然产物、生物活性分子、药物等相关化合物以及许多其他精细化学品中.近年来,发展了大量的合成方法制备该类化合物.其中,可见光诱导的l,n-烯炔的自由基串联环化反应条件绿色友好、操作简单、化学选择性和官能团兼容性好,已成为制备该类化合物的强有力工具.本文主要根据自由基产生的类型概述了近来可见光诱导的...     

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.     

Diastereo- and Enantioselective Mannich/Cyclization Cascade Reaction Access to Chiral Benzothiazolopyrimidine Derivatives

An efficient asymmetric Mannich/cyclization cascade strategy was established from 2-benzothiazolimines with N-acylpyrazoles to provide optical active benzothiazolopyrimidine derivatives using a copper-based complex. The mild cascade process constructed various structurally diverse products with broad scope of substrates together with excellent enantioselectivities (up to 99 % ee) and diastereoselectivities (up to 99:1 d.r.).     

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.     

Total Synthesis of Ovafolinins A and B: Unique Polycyclic Benzoxepin Lignans through a Cascade Cyclization

Ovafolinins A and B, isolated from Lyonia ovalifolia var. elliptica, are lignans that contain a unique bridged structure containing a penta‐ and tetracyclic benzoxepin and an aryl tetralin. We report the first total synthesis of these natural products in which an acyl‐Claisen rearrangement was initially utilized to construct the lignan backbone with correct relative stereochemistry. Judicious use of a bulky protecting group placed reactive moieties in the correct orientation, thereby resulting in a cascade reaction to form the bridged benzoxepin/aryl tetralin from a linear precursor in a single step. Modification of this route allowed the enantioselective synthesis of (+)‐ovafolinins A and B, which confirmed the absolute stereochemistry, and comparison of optical rotation suggests that these compounds are found as scalemic mixtures in nature.     

Pyramidalized Alkenes: Theory and Experiment

Structural X-ray data on highly strained anti-Bredt olefins (see, for instance, J. Am. Chem. Soc. 1990 1128627) prompted us to perform model ab initio calculations with the 6-31G* basis set for ethylene and its simple derivatives. A variety of modes of distortion for ethylene were examined: deformations in plane, pyramidalization, and twist. Olefinic atoms are found to be spontaneously pyramidalized either (1) under the influence of certain substituents that break the original symmetry of a molecule, or (2) when a distortion is introduced in a molecule that simulates the cyclization. Furthermore, pyramidalization is enhanced when a bond angle deformation takes place. The stereochemistry of C=C and Si=Si is briefly compared and discussed.     

De Novo Synthesis of Highly Functionalized Benzimidazolones and Benzoxazolones through an Electrochemical Dehydrogenative Cyclization Cascade

Benzimidazolone and benzoxazolone moieties are important scaffolds in a variety of pharmaceutical molecules. These bicyclic heterocycles are usually prepared from a benzene derivative through the construction of an additional five‐membered heterocyclic ring. We report herein a method that enables the efficient synthesis of highly substituted benzimidazolone and benzoxazolone derivatives by building both the benzene and the heterocyclic rings through a dehydrogenative cyclization cascade. Readily available arylamine‐tethered 1,5‐enynes undergo a biscyclization/dehydrogenation cascade to afford functionalized benzanellated heterocycles in a single step with complete control of regioselectivity. These electricity‐powered oxidative transformations proceed with H₂ evolution, thus obviating the need for transition‐metal‐based catalysts and oxidizing reagents.     

Organic Photocatalytic Cyclization of Polyenes: A Visible‐Light‐Mediated Radical Cascade Approach

A visible‐light‐mediated, organic photocatalytic stereoselective radical cascade cyclization of polyprenoids is described. The desired cascade cyclization products are achieved in good yields and high stereoselectivities with eosin Y as photocatalyst in hexafluoro‐2‐propanol. The catalyst system is also suitable for 1,3‐dicarbonyl compounds, which require only catalytic amounts of LiBr to promote the formation of the corresponding enols.     

Silver-Catalyzed Cascade Cyclization of Amino-NH-1,2,3-Triazoles with 2-Alkynylbenzaldehydes: An Access to Pentacyclic Fused Triazoles

An operationally simple Ag(I)-catalyzed approach for the synthesis of isoquinoline and quinazoline fused 1,2,3-triazoles was developed by a condensation and amination cyclization cascade of amino-NH-1,2,3-triazoles with 2-alkynylbenzaldehydes involving three new C-N bond formations in one manipulation, in which the group of -NH of the triazole ring serves as a nucleophile to form the quinazoline skeleton. The efficient protocol can be applied to a variety of substrates containing a range of functional groups, delivering novel pentacyclic fused 1,2,3-triazoles in good-to-excellent yields.