Construction Of Ring Research Articles

Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation.

Axially chiral biaryls, as exemplified by 1,1'-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in enantioenriched form through metal-mediated cross coupling, de novo construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed O-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective O-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to C2-symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective O-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.

Synthetic Strategies for Peroxide Ring Construction in Artemisinin.

The present review summarizes publications on the artemisinin peroxide fragment synthesis from 1983 to 2016. The data are classified according to the structures of a precursor used in the key peroxidation step of artemisinin peroxide cycle synthesis. The first part of the review comprises the construction of artemisinin peroxide fragment in total syntheses, in which peroxide artemisinin ring resulted from reactions of unsaturated keto derivatives with singlet oxygen or ozone. In the second part, the methods of artemisinin synthesis based on transformations of dihydroartemisinic acid are highlighted.

PS-Modules over Generalized Malcev-Neumann Series

In [1], the rst author introduced a new class of extension rings called the generalized Malcev-Neumann series ring $R((S;\sigma;\tau))$ with coeffcients in a ring $R$ and exponents in a strictly ordered monoid $S$ which extends the usual construction of Malcev-Neumann series rings. The conditions under which the generalized Malcev-Neumann series module $M((S))_{R ((S;\sigma;\tau)) }$ is a PS-module are investigated in the present paper.

Copper-catalyzed construction of eight-membered rings via oxidative ring expansion and intermolecular cyclization sequencing of indoles with amidines: efficient synthesis of benzo[1,3,5]triazocin-6(5H)-ones.

Novel and efficient synthesis of eight-membered nitrogen heterocycles in one pot by copper-catalyzed oxidative ring expansion and intermolecular cyclization sequencing of indoles with amidines has been described. This protocol features easily available substrates and high step-economy. More importantly, dioxygen as the most ideal oxidant was employed under mild reaction conditions. A variety of valuable benzo[1,3,5]triazocin-6(5H)-one derivatives bearing functional groups were assembled in middle to good yields.

Synthesis of functionalized indolizines via gold(i)-catalyzed intramolecular hydroarylation/aromatization of pyrrole-ynes.

A gold-catalyzed intramolecular hydroarylation/aromatization of pyrrole-ynes has been developed. This method provides a concise and straightforward route to functionalized indolizines through the construction of the pyridine ring of indolizines and also allows elaboration of its pyrrole moiety with or without functional groups. In addition, a wide variety of functional groups, such as aryl, alkenyl, alkynyl, pyridyl or thienyl groups, can be easily incorporated into the pyridine unit of the indolizine products under mild conditions. The utility of the indolizine products was demonstrated by their efficient transformations into various C3-functionalized indolizine derivatives.

Diastereoselective tandem oxidation/Michael/aldol reaction: unprecedented formation of dispirocyclopentanebisoxindoles and dispiro[acenaphthylene-1,1′-cyclopentane-3′,1′′-acenaphthylene]-2,2′′diones

An unprecedented tandem oxidation/Michael/aldol reaction is reported. The diastereoselective formation of only a single isomer of dispirocyclopentanebisoxindole and dispiro[acenaphthylene-1,1'-cyclopentane-3',1''-acenaphthylene]-2,2''dione is presented. The reaction generates two new C-C bonds and two all-carbon quaternary chiral stereocenters in a single step.

Mn(OAc)3-Mediated Synthesis of 3-Phosphonyldihydrofurans from β-Ketophosphonates and Alkenes

A new, general method for the synthesis of 3-phosphonyldihydrofuran derivatives has been achieved through Mn(OAc)3-mediated radical cyclization between β-ketophosphonates and alkenes. This transformation allows the direct formation of C–C/C–O bonds and the construction of a dihydrofuran ring in one reaction with operational simplicity and excellent functional-group compatibility.

ChemInform Abstract: Metal‐Free Synthesis of Fully Substituted Pyridines via Ring Construction Based on the Domino Reactions of Enaminones and Aldehydes.

AbstractThe reaction can be scaled up.

A new paradigm for designing ring construction strategies for green organic synthesis: implications for the discovery of multicomponent reactions to build molecules containing a single ring.

A new way of developing novel synthesis strategies for the construction of monocyclic rings found in organic molecules is presented. The method is based on the visual application of integer partitioning to chemical structures. Two problems are addressed: (1) the determination of the total number of possible ways to construct a given ring by 2-, 3-, and 4-component couplings; and (2) the systematic enumeration of those possibilities. The results of the method are illustrated using cyclohexanone, pyrazole, and the Biginelli adduct as target ring systems with a view to discover new and greener strategies for their construction using multicomponent reactions. The application of the method is also extended to various heterocycles found in many natural products and pharmaceuticals.

The Assembly and Application of 'Shear Rings': A Novel Endothelial Model for Orbital, Unidirectional and Periodic Fluid Flow and Shear Stress.

Deviations from normal levels and patterns of vascular fluid shear play important roles in vascular physiology and pathophysiology by inducing adaptive as well as pathological changes in endothelial phenotype and gene expression. In particular, maladaptive effects of periodic, unidirectional flow induced shear stress can trigger a variety of effects on several vascular cell types, particularly endothelial cells. While by now endothelial cells from diverse anatomic origins have been cultured, in-depth analyses of their responses to fluid shear have been hampered by the relative complexity of shear models (e.g., parallel plate flow chamber, cone and plate flow model). While these all represent excellent approaches, such models are technically complicated and suffer from drawbacks including relatively lengthy and complex setup time, low surface areas, requirements for pumps and pressurization often requiring sealants and gaskets, creating challenges to both maintenance of sterility and an inability to run multiple experiments. However, if higher throughput models of flow and shear were available, greater progress on vascular endothelial shear responses, particularly periodic shear research at the molecular level, might be more rapidly advanced. Here, we describe the construction and use of shear rings: a novel, simple-to-assemble, and inexpensive tissue culture model with a relatively large surface area that easily allows for a high number of experimental replicates in unidirectional, periodic shear stress studies on endothelial cells.

Apparent Carbon Monoxide Insertion via Double Isocyanide Incorporation during Palladium‐Catalyzed Construction of Indoloquinoline Ring in a Single Pot: Synthesis of New Cytotoxic Agents

AbstractThe formation of an amide bond via incorporation of two isocyanide units during a palladium‐catalyzed construction of the indoloquinoline ring afforded N‐substituted 6H‐indolo[2,3‐b]quinoline‐11‐carboxamides as new cytotoxic agents. The solvent and base play a key role in the selective and unprecedented synthesis of this class of amides.magnified image

Sunlight-Driven Forging of Amide/Ester Bonds from Three Independent Components: An Approach to Carbamates.

A photoredox catalytic route to carbamates enabled by visible irradiation (or simply sunlight) has been developed. This process leads to a novel approach to the construction of heterocyclic rings wherein the amide or ester motifs of carbamates were assembled from three isolated components. Large-scale experiments were realized by employing continuous flow techniques, and reuse of photocatalyst demonstrated the green and sustainable aspects of this method.

Hexadehydro-Diels-Alder (HDDA)-Enabled Carbazolyne Chemistry: Single Step, de Novo Construction of the Pyranocarbazole Core of Alkaloids of the Murraya koenigii (Curry Tree) Family.

Here we report the use of the hexadehydro-Diels-Alder (HDDA) reaction for the de novo construction of a benzenoid ring in fused polycyclic heteroaromatic carbazole (i.e., [2,3]-benzoindole) skeletons. The strategy allows creation of highly substituted benzenoids. We also describe the HDDA-enabled chemical synthesis of the natural product alkaloids mahanimbine and koenidine. Trapping of the intermediate carbazolyne with a conjugated enal, proceeding through formal [2+2] cycloaddition, 4π-electrocyclic ring opening, and 6π-electrocyclic ring-closing events, constitutes a robust method for producing pyranocarbazoles.

Expanding the socle of a codimension 3 complete intersection

A quotient ring of a regular local ring of embedding dimension~3 has a minimal free resolution that carries a differential graded algebra structure. This structure has been used to classify such rings. For some classes very few examples have been observed. One such class is called \lt B>{B}\lt /B>, named for Anne Brown, who discovered and gave the first constructions of rings in this class. Her constructions were the only known rings in that class until recently. In this paper, we show how to obtain Artinian rings in the class \textbf {B} by expanding the socle of a complete intersection.

ChemInform Abstract: Synthesis of 3H‐Pyrroles (Microreview)

AbstractReview: 26 refs.

ChemInform Abstract: (Hetero)aromatics from Dienynes, Enediynes and Enyne—Allenes

AbstractReview: 216 refs.

ChemInform Abstract: AlCl3‐Mediated Heteroarylation‐Cyclization Strategy: One‐Pot Synthesis of Fused Quinoxalines Containing the Central Core of Lamellarin D.

AbstractPyrano[3,4‐b]indole fused quinoxalines are synthesized from 1,2‐dichloroquinoxalines and indole‐2‐carboxylic acids using the title strategy.

Synthesis of 1,4-diarylpyrrolotriazepine derivatives by two diverse strategies

1,4-Diaryl-5H-pyrrolo[2,1-d][1,2,5]triazepines were prepared by two different pathways. In the first case, the condensation reaction of the appropriate diketones with hydrazine monohydrate was applied for the construction of the seven-membered triazepine ring. In the second case, previously prepared intermediates, 1-aryl-3H-pyrrolo[2,1-d][1,2,5]triazepine-4(5H)-thiones were used as starting materials. The arylation of these thioamides were carried out with boronic acids in Liebeskind-Srogl palladium-catalysed cross-coupling reaction.

A mild acid-free one-pot reaction for synthesis of new phenanthridine dyes

A series of new phenylphenanthridin dyes have been synthesized in the yields of 52–75% by a mild strategy in one-pot reaction. This is the first successful attempt to perform efficient soft acid-free reaction for phenanthridine ring construction. A large substrate scope was well demonstrated.

An Alternative Perspective on Skew Generalized Power Series Rings

This paper continues the ongoing effort to study the structure of the set of nilpotent elements in noncommutative ring constructions. Let R be any ring, \({(S,\leq)}\) a strictly (partially) ordered monoid and also \({\omega:S\rightarrow}\) End(R) a monoid homomorphism. A skew generalized power series ring \({R[[{S,\omega\leq}}]]\) consists of all functions from a monoid S to a coefficient ring R, whose support contains neither infinite descending chains nor infinite antichains, with pointwise addition, and with multiplication given by convolution twisted by an action \({\omega}\) of the monoid S on the ring R. Our studies in this paper is strongly connected to the question of whether or not a skew generalized power series ring \({R[[{S,\omega\leq}}]]\) over a nil coefficient ring R is nil, which is related to the famous question of Amitsur. However, we show that under mild “Armendariz-like” hypothesis on a coefficient ring R, we obtain stronger conditions on the coefficients of elements of a skew generalized power series ring \({R[[{S,\omega\leq}}]]\). We will also explore some annihilator conditions in the skew generalized power series ring setting, unifying and generalizing a number of known Armendariz-like and McCoy-like conditions in the special cases.