Construction Of Ring Research Articles

Ring Construction by 1,1‐Carboboration; Making Anthracene Derivatives from a Tetra(alkynyl)benzene

Abstract1,2,4,5‐Tetrakis(trimethylsilylethynyl)benzene reacted with two molar equivalents of the boranes R−B(C6F5)2 (R=C6F5, Me, Ph) in a series of sequential 1,1‐carboboration reactions to give ca. 1 : 1 mixtures of the two‐fold benzannulated products, namely the respective C2h and C2v symmetric tetra‐silyl, bis‐boryl substituted anthracenes. Their active B(C6F5)2 substituents were used for consecutive Suzuki‐Miyaura C−C coupling reactions to give boron‐free phenyl or 2‐pyridyl substituted anthracene products.

Synthetic Strategies for the (+)-Grandisol, the Main Constituent of Boll Weevil Pheromone

This paper presents a short review of synthetic approaches aiming to synthesise (+)- Grandisol, the main constituent of grandlure, a pheromone mixture released by the boll weevil, which is proven to exhibit significant biological activity. (+)-Grandisol 1 is among the components of the male-produced pheromone of the boll weevil Anthonomuns grandis, an important pest of cotton crops in Mesoamerica (from the south USA to Argentina). As a result of its biological activity and unique structure, several synthetic approaches have been reported. The aim is to explore remarkable methodologies towards the synthesis of (+)-Grandisol 1. Several methodologies have been applied towards the synthesis of (+)-Grandisol 1, including classical methods for cyclobutane ring construction, which promoted substantial improvements to access this pheromone, as well as a better comprehension of its biological profile.

Synthesis of Highly Substituted Biaryls by the Construction of a Benzene Ring via In Situ Formed Acetals.

Herein, we present an interesting method for the construction of a benzene ring using propargylic alcohols and 1,3-dicarbonyls, which involves three new C-C bond formations via cascade alkylation, formylation, annulation, and aromatization to make substituted biaryls. This one-pot Brønsted acid-promoted protocol utilizes the unique reactivity of the acetal formed under the reaction conditions. Alkynyl methyl ketones could be employed instead of 1,3-dicarbonyls as they are converted to 1,3-dicarbonyls by hydration under the reaction conditions.

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.

On the integral domains characterized by a Bezout property on intersections of principal ideals

In this article we study two classes of integral domains. The first is characterized by having a finite intersection of principal ideals being finitely generated only when it is principal. The second class consists of the integral domains in which a finite intersection of principal ideals is always non-finitely generated except in the case of containment of one of the principal ideals in all the others. We relate these classes to many well-studied classes of integral domains, to star operations and to classical and new ring constructions.

Copper-Catalyzed Aminoheteroarylation of Unactivated Alkenes through Distal Heteroaryl Migration.

We report a copper-catalyzed aminoheteroarylation of unactivated alkenes to access valuable heteroarylethylamine motif. The developed reaction features a copper-catalyzed intermolecular electrophilic amination of the alkenes followed by a migratory heteroarylation. The method applies on alcohol-, amide-, and ether-containing alkenes, overcoming the common requirement of a hydroxyl motif in previous migratory difunctionalization reactions. This reaction is effective for the introduction of diverse aliphatic amines and has good functional group tolerance, which is particularly useful for richly functionalized heteroarenes. This migration-involved reaction was found well suited as a powerful ring expansion approach for the construction of medium-sized rings that are in great demand in medicinal chemistry.

Designing and Accurately Developing a [6 + 2] Dipolar Cycloaddition for the Synthesis of Benzodiazocines.

1,6-Dipolar cycloadditions represent a valuable strategy for the rapid construction of medium-sized rings. Herein, we describe the concept for the design of 1,6-dipoles that bypasses the regioselectivity. Through the introduction of an amino group into Morita-Baylis-Hillman (MBH) carbonates, unprecedented [6 + 2] dipolar cycloadditions were accurately developed with Cs2CO3, efficiently delivering a series of benzodiazocines in mild conditions. Computational studies bring a deeper understanding of this reaction.

Enantioselective Organocatalytic Syntheses and Ring‐Expansions of Cyclobutane Derivatives

AbstractThe progress in enantioselective organocatalysis have enabled efficient and highly stereoselective syntheses of cyclobutane derivatives, through (2+2) annulation reactions, overcoming the geometrical constraints inherent to these small cyclic molecules. More importantly, and taking advantage of their strain‐releasing fragmentation, some cyclobutane derivatives, especially cyclobutanones and cyclobutenones, can now be regarded as versatile four‐carbon atoms units amenable to the enantioselective construction of larger rings by (4+n) annulation reactions to produce, five‐, six‐, seven‐ and eight‐membered cyclic products. These recent developments concerning the enantioselective synthetic chemistry of cyclobutane derivatives under organocatalytic conditions are reviewed herein.

Propargylamines in Pd/Cu-catalyzed tandem coupling-cyclization-N-deprotection in a single pot: Construction of N-unsubstituted vs N-sulfonyl indole ring

The Pd/Cu-catalyzed tandem coupling–cyclization-N-deprotection in a single pot (Method a) vs sequential coupling–cyclization under similar conditions (Method b) has been studied using propargylamine as a terminal alkyne under environmentally friendly conditions. The first sequence (Method a) was followed to afford the N-unsubstituted indoles when 2,2,2-trifluoro-N-(2-iodophenyl)acetamides were employed as halides whereas N-sulfonyl indoles were obtained following the second path (Method b) when 2-iodo sulfanilides were used as halides. A number of compounds based on either the framework indolo[2,3–b]quinoxaline-indole or a similar framework possessing a sulfonyl group at the indole nitrogen were obtained in good yield employing the Method a or b, respectively. While the study was carried out with the goal of accessing a library of indolo[2,3–b]quinoxaline-indole based small molecules of potential biological interest (especially as anti-tubercular agents) the generality/scope of Method a was expanded further via the synthesis of simpler indole derivatives using various other propargylamines as terminal alkynes.

Construction 7-membered ring via Ni\u2013Al bimetal-enabled C\u2013H cyclization for synthesis of tricyclic imidazoles

The construction of 7-membered ring via direct C7–H cyclization of benzoimidazoles with alkenes would provide a more atom- and step-economical route to tricyclic imidazoles and derivatives that widely exist in a broad range of bioactive molecules. However, transition metal-catalyzed C–H cyclization for medium-ring synthesis has been limited to reactive C–H bonds, instead, the activation of unreactive C–H bonds towards medium synthesis still remains an elusive challenge. Herein, we report a direct construction of 7-membered rings via Ni–Al co-catalyzed unreactive C7–H cyclization of benzoimidazoles with alkenes, providing a series of tricyclic imidazoles in 40–98% yield and with up to 95:5 er.

Enantioselective Synthesis of Axially Chiral Benzothiophene/Benzofuran-Fused Biaryls by N-Heterocyclic Carbene Catalyzed Arene Formation.

Axially chiral biaryl scaffolds are prevalent in natural products, chiral ligands, and organocatalysts. However, N-heterocyclic carbene (NHC) catalyzed de novo construction of an aromatic ring with concomitant axial chirality induction for the synthesis of biaryl atropisomers is far less developed, and the efficient synthesis of axially chiral tetra-ortho-substituted biaryls remains an unsolved problem under NHC catalysis. Reported here is an NHC-catalyzed de novo synthesis of axially chiral benzothiophene/benzofuran-fused biaryls from enals and 2-benzyl-benzothiophene/benzofuran-3-carbaldehydes through a [2+4] annulation, decarboxylation, and oxidative aromatization cascade with central-to-axial chirality conversion. The developed method provides efficient and general access to novel axially chiral benzothiophene/benzofuran-fused biaryls in high enantioselectivities and works well for the synthesis of tetra-ortho-substituted biaryls.

Enantioselective Synthesis of Axially Chiral Benzothiophene/Benzofuran‐Fused Biaryls by N‐Heterocyclic Carbene Catalyzed Arene Formation

AbstractAxially chiral biaryl scaffolds are prevalent in natural products, chiral ligands, and organocatalysts. However, N‐heterocyclic carbene (NHC) catalyzed de novo construction of an aromatic ring with concomitant axial chirality induction for the synthesis of biaryl atropisomers is far less developed, and the efficient synthesis of axially chiral tetra‐ortho‐substituted biaryls remains an unsolved problem under NHC catalysis. Reported here is an NHC‐catalyzed de novo synthesis of axially chiral benzothiophene/benzofuran‐fused biaryls from enals and 2‐benzyl‐benzothiophene/benzofuran‐3‐carbaldehydes through a [2+4] annulation, decarboxylation, and oxidative aromatization cascade with central‐to‐axial chirality conversion. The developed method provides efficient and general access to novel axially chiral benzothiophene/benzofuran‐fused biaryls in high enantioselectivities and works well for the synthesis of tetra‐ortho‐substituted biaryls.

Isoquinolone Syntheses by Annulation Protocols

Isoquinolones (isoquinolin-1(2H)-ones) are one of the important nitrogen-heterocyclic compounds having versatile biological and physiological activities, and their synthetic methods have been recently developed greatly. This short review illustrates the significant advances in the construction of isoquinolone ring with atom- and step-economy, focusing on the intermolecular annulation protocols and intramolecular cyclization in the presence of a variety of catalyst systems. The syntheses of isoquinolone-fused rings are also included.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[ 1,5-a]pyrimidines.

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude, hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5- a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β- ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones "1,2-allenic", unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The routes adopted to synthesize this class of heterocyclic compounds were extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.

Phosphirenium Ions as Masked Phosphenium Catalysts: Mechanistic Evaluation and Application in Synthesis.

The utilization of phosphirenium ions is presented; optimized and broadened three-membered ring construction is described together with the use of these ions as efficient pre-catalysts for metal-free carbonyl reduction with silanes. Full characterization of the phosphirenium ions is presented, and initial experimental and computational mechanistic studies indicate that these act as a “masked phosphenium” source that is accessed via ring opening. Catalysis proceeds via associative transfer of {Ph2P+} to a carbonyl nucleophile, H–SiR3 bond addition over the C=O group, and associative displacement of the product by a further equivalent of the carbonyl substrate, which completes the catalytic cycle. A competing off-cycle process leading to vinyl phosphine formation is detailed for the hydrosilylation of benzophenone for which an inverse order in [silane] is observed. Experimentally, the formation of side products, including off-cycle vinyl phosphine, is favored by electron-donating substituents on the phosphirenium cation, while catalytic hydrosilylation is promoted by electron-withdrawing substituents. These observations are rationalized in parallel computational studies.

Linear Control Method for Arch Ring of Oblique-Stayed Buckle Cantilever Pouring Reinforced Concrete Arch Bridge

Yelang Lake Bridge is the largest cantilevered single-chamber reinforced concrete arch bridge in China, with a net span of 210 m. In this article, an equation for positioning the height of the formwork before pouring of the arch ring segment was derived, which was suitable for the construction control of the long-span reinforced concrete arch bridge such as the Yelang Lake Bridge. The arch ring segment elevation calculation equation was derived under the two typical working conditions that the concrete pouring of the arch ring segment is completed and the buckle cable and anchor cable tensioning are completed. In addition, two typical working conditions of arch ring segment concrete pouring and cable tensioning were evaluated. Then, a new type of cradle and loading test of the cradle, which meet the requirements of the long segment pouring of the arch ring, were introduced. Finally, the measurement deviation during the construction of the arch segment was analyzed. The linear control results of the arch ring showed that the arch ring segment elevation calculation formula could effectively ensure the accuracy of the arch ring segment construction process under the two typical conditions of completion of concrete pouring of the arch ring segment and completion of the buckle and anchor cable tensioning. The maximum deviation is only 3.1 mm. The line shape after the completion of the arch ring construction was in good agreement with the target line shape, and the deviation between the measured value and the target value was only 2.5 cm, which met the engineering requirements.

Concise total synthesis of nauclefine: A regioselective Rhodium(III)-catalyzed oxidative C-H activation approach

Abstract A concise total synthesis of the plant indole alkaloid natural product nauclefine (1) was accomplished from the commercially available nicotinic acid and the known compound in 6 steps. The synthesis features a regioselective rhodium(III)-catalyzed oxidative C-H activation for the construction of the key naphthyridinone ring. The intramolecular Mitsunobu-type annulation, allylic oxidation and Fischer indolization were used successively to complete the total synthesis of nauclefine (1).

Group matrix ring codes and constructions of self-dual codes

In this work, we study codes generated by elements that come from group matrix rings. We present a matrix construction which we use to generate codes in two different ambient spaces: the matrix ring M_k(R) and the ring R, where R is the commutative Frobenius ring. We show that codes over the ring M_k(R) are one sided ideals in the group matrix ring M_k(R)G and the corresponding codes over the ring R are G^k-codes of length kn. Additionally, we give a generator matrix for self-dual codes, which consist of the mentioned above matrix construction. We employ this generator matrix to search for binary self-dual codes with parameters [72, 36, 12] and find new singly-even and doubly-even codes of this type. In particular, we construct 16 new Type I and 4 new Type II binary [72, 36, 12] self-dual codes.

Consecutive O−S/N−S Bond Cleavage in Gold‐Catalyzed Rearrangement Reactions of Alkynyl N‐Sulfinylimines

AbstractGold‐catalyzed reactions of alkynyl N‐sulfinylimines were used to produce the corresponding 2H‐azirines possessing sulfenyl and acyl groups at the 3‐position of the azirine ring in good to excellent yields. These reactions involved internal transfer of the sulfinyl oxygen atom to form a thiooxime intermediate tethered to an α‐oxo gold carbene moiety. Subsequent insertion of the carbene into the N−S bond resulted in ring construction.

Palladium-Catalyzed [4 + 3] or [2 + 2 + 3] Annulation via C-H Activation and Subsequent Decarboxylation: Access to Heptagon-Embedded Polycyclic Aromatic Hydrocarbons.

The construction of a seven-membered ring in the polycyclic aromatic hydrocarbon skeleton remains a notoriously difficult but attractive challenge. Herein a novel palladium-catalyzed [4 + 3] decarboxylative annulation of 2-iodobiphenyls with 2-(2-halophenyl)acrylic acids is reported, which provides an efficient approach for assembling various tribenzo[7]annulenes via a C-H activation and decarboxylation process. Moreover, tribenzo[7]annulenes can be also synthesized via a [2 + 2 + 3] decarboxylative annulation strategy by employing readily available 1,2-halobenzenes, phenylboronic acids, and 2-(2-halophenyl)acrylic acids.