Electrochemical Cross-Coupling between N-(4-Hydroxyphenyl)-sulfonamides and 2-Naphthols: Synthesis of 2,2'-Bis(arenol)s.

We herein present an electrochemical method for the dehydrogenative cross-coupling of N-(4-hydroxyphenyl)-sulfonamides and 2-naphthols. This transformation provides a direct and scalable approach to a wide range of C1-symmetric 2,2'-bis(arenol)s with moderate to high yields under mild conditions. Preliminary attempts with the asymmetric variant of this reaction were also performed with ≤55% ee for the synthesis of 2,2'-bis(arenol)s. Control experiments were conducted to propose a plausible mechanism for the reaction.

Phosphoric Acid-Catalyzed Enantioselective Synthesis of Axially Chiral Anthrone-based Compounds.

Anthrones and analogues are structural cores shared by diverse pharmacologically active natural and synthetic compounds. The sp2 -rich nature imposes inherent obstruction to introduce stereogenic element onto the tricyclic aromatic backbone. In our pursuit to expand the chemical space of axial chirality, a novel type of axially chiral anthrone-derived skeleton was discovered. This work establishes oxime ether as suitable functionality to furnish axial chirality on symmetric anthrone skeletons through stereoselective condensation of the carbonyl entity with long-range chirality control. The enantioenriched anthrones could be elaborated into dibenzo-fused seven-membered N-heterocycles containing well-defined stereogenic center via Beckmann rearrangement with axial-to-point chirality conversion.

Asymmetric Pnictogen-Bonding Catalysis: Transfer Hydrogenation by a Chiral Antimony(V) Cation/Anion Pair.

Pnictogen-bonding catalysis based on σ-hole interactions has recently attracted the attention of synthetic chemists. As a proof-of-concept for asymmetric pnictogen-bonding catalysis, we report herein an enantioselective transfer hydrogenation of benzoxazines catalyzed by a novel chiral antimony cation/anion pair. The chiral pnictogen catalyst library could be rapidly accessed from triarylstibine with readily available mandelic acid analogues, and the catalyst displays remarkable efficiency and enantiocontrol potency even at 0.05 mol % loading. Moreover, the properties of the catalyst and the mechanistic insights have been investigated by nonlinear effect studies, 1H NMR, LC-MS, and control experiments.

Nitrosobenzene-Enabled Chiral Phosphoric Acid Catalyzed Enantioselective Construction of Atropisomeric N-Arylbenzimidazoles.

Described herein is an imidazole ring formation strategy for the synthesis of axially chiral N-arylbenzimidazoles by means of chiral phosphoric acid catalysis. Two sets of conditions were developed to transform two classes of 2-naphthylamine derivatives into structurally diverse N-arylbenzimidazole atropisomers with excellent chemo- and regioselectivity as well as high levels of enantiocontrol. It is worth reflecting on the unique roles played by the nitroso group in this domino reaction. It functions as a linchpin by first offering an electrophilic site (N) for the initial C-N bond formation while the resulting amine performs the nucleophilic addition to form the second C-N bond. Additionally, it could facilitate the final oxidative aromatization as an oxidant. The atropisomeric products could be conveniently elaborated to a series of axially chiral derivatives, enabling the exploitation of N-arylbenzimidazoles for their potential utilities in asymmetric catalysis.

ß-C-Glycosylation with 2-Oxindole Acceptors via Palladium-Catalyzed Decarboxylative Reactions.

This report describes a highly efficient ß-selective C-glycosylation of bicyclic galactals with 2-oxindoles through a palladium-catalyzed decarboxylative pathway. A variety of substrates representing both glycosyl donors and acceptors could be transformed in greater than 90% yields under mild reaction conditions. The decarboxylation intermediate of galactal could serve as an efficient base to deprotonate the enol tautomer of 2-oxindole and enhance its nucleophilicity. The ß-selective nucleophilic addition at the anomeric center originates from the steric hindrance imposed by the palladium and bulky ligand.

Enantioselective Cu-catalyzed double hydroboration of alkynes to access chiral gem-diborylalkanes.

Chiral organoborons are of great value in asymmetric synthesis, functional materials, and medicinal chemistry. The development of chiral bis(boryl) alkanes, especially optically enriched 1,1-diboron compounds, has been greatly inhibited by the lack of direct synthetic protocols. Therefore, it is very challenging to develop a simple and effective strategy to obtain chiral 1,1-diborylalkanes. Herein, we develop an enantioselective copper-catalyzed cascade double hydroboration of terminal alkynes and highly enantioenriched gem-diborylalkanes were readily obtained. Our strategy uses simple terminal alkynes and two different boranes to construct valuable chiral gem-bis(boryl) alkanes with one catalytic and one ligand pattern, which represents the simplest and most straightforward strategy for constructing such chiral gem-diborons.

Isolation, Total Synthesis, and Absolute Configuration Determination of Renoprotective Dimeric N-Acetyldopamine-Adenine Hybrids from the Insect Aspongopus chinensis.

Aspongdopamines A and B (1 and 2), unusual adducts composed of N-acetyldopamine and adenine were isolated from the insect Aspongopus chinensis. Compounds 1 and 2 are positional isomers both isolated as racemates. Chiral separation assisted by 14-step total synthesis and computation including vibrational circular dichroism calculations allowed us to unambiguously assign the absolute configurations of eight stereoisomers. Renal fibrosis inhibition of the stereoisomers was evaluated in TGF-ß1-induced rat kidney epithelial cells.