Synthesis of 7-Arylthiomethyl Dibenzo[b,d]azepines through Imidoylative Heck Cyclization and CPA-Catalyzed Thio-Michael Addition/Enantioselective Protonation

Enhanced Pyridine-Oxazoline Ligand-Enabled Pd(II)-Catalyzed Aminoacetoxylation of Alkenes for the Asymmetric Synthesis of Biaryl-Bridged 7-Membered N-Heterocycles and Atropisomers

A new class of binaphthyl unit-enhanced pyridine-oxazoline ligands was developed to promote the Pd-catalyzed enantioselective intramolecular 7-exo aminoacetoxylation of unactivated biaryl alkenes. Biaryl-bridged 7-membered N-heterocycles bearing a chiral center were obtained in good yields with excellent enantioselectivities (up to 99:1 er). Computational investigations on a series of biaryl-bridged 7-membered rings provided insights into the rotational barrier of the potentially chiral biaryl unit by the substituent effect including the heteroatom, the protecting group, and the chiral center. The kinetic resolution of racemic axially chiral biaryls via intramolecular enantioselective aminoacetoxylation of alkenes has also been achieved, affording previously inaccessible biaryl-bridged 7-membered N-heterocycles bearing both a chiral center and a chiral axis, as well as axially chiral biaryl amino alcohols.

Regiospecific 2,3-Dialkylindole Synthesis Enabled by Alkylpalladium 1,2-Migration to In Situ Formed Aldimine

2,3-Dialkylindoles play crucial roles in natural products and pharmaceuticals, but the step-efficient and regioselective construction of such privileged structures remains a long-standing challenge. Here, we report a regiospecific non-Fischer indole synthesis through chemoselective 1,2-migratory addition of alkylpalladium to an aldimine intermediate, formed in situ through a palladium hydride-triggered sequential isocyanide and intramolecular olefin insertion. This unprecedented 1,2-migratory addition leads to formal C═C bond cleavage and isocyano carbon insertion between the two sp2 carbons, offering a novel approach to specific 2,3-dialkyl substituted N─H free indoles from readily available alkyl substituted 1-isocyano-2-vinylbenzenes.

Access to Chiral Bridged Biaryls via Brønsted Acid-Catalyzed Asymmetric Addition of Alcohols to Fluoroalkylated Biaryl Oxazepines

We disclose herein a chiral phosphoric-acid-catalyzed enantioselective addition reaction of alcohols to fluoroalkylated biaryl 1,3-oxoazepines, which furnished a wide range of bridged biaryls bearing a fluoroalkylated quaternary carbon stereocenter on the seven-membered ring in high yields (up to 99%) with excellent enantioselectivities (up to 98% ee). Our method can be used for the modification of several natural products and bioactive molecules. Preliminary studies revealed that the products obtained in this reaction exhibit good in vitro bioactivities against two plant pathogens.

Stereoselective Enesulfinamide-Sulfinylimine Tautomerization of β,β-Disubstituted Enesulfinamides

In the presence of cesium fluoride and organosilicon reagent, β,β-disubstituted NH-enesulfinamides undergo stereoselective enesulfinamide-sulfinylimine tautomerization at room temperature, resulting in the formation of α-branched N-sulfinyl ketimines in good yields with high stereoselectivity. A variety of acyclic ketone surrogates α-substituted with two electronically and sterically similar groups (e.g., methyl and ethyl), which are typically challenging to access through conventional protocols involving stereoselective protonation of enolates and their equivalents, have been effectively synthesized.

Synthesis of easily-modified and useful dibenzo-[b,d]azepines by palladium(II)-catalyzed cyclization/addition with a green solvent

A novel strategy in which palladium(II)-catalyzed tandem cyclization is used to obtain N-heterocyclic architectures containing a seven-membered ring has been developed and used to synthesize a series of derivatives. The reaction uses an eco-friendly mixed solvent (water : EtOH = 2 : 1) instead of DMSO and maintains a high yield (91%). Its potential application value and reaction mechanism have also been explored.

Catalytic Asymmetric Synthesis of Atropisomers Bearing Multiple Chiral Elements: An Emerging Field

With the rapid development of asymmetric catalysis, the demand for the enantioselective synthesis of complex and diverse molecules with different chiral elements is increasing. Owing to the unique features of atropisomerism, the catalytic asymmetric synthesis of atropisomers has attracted a considerable interest from the chemical science community. In particular, introducing additional chiral elements, such as carbon centered chirality, heteroatomic chirality, planar chirality, and helical chirality, into atropisomers provides an opportunity to incorporate new properties into axially chiral compounds, thus expanding the potential applications of atropisomers. Thus, it is important to perform catalytic asymmetric transformations to synthesize atropisomers bearing multiple chiral elements. In spite of challenges in such transformations, in recent years, chemists have devised powerful strategies under asymmetric organocatalysis or metal catalysis, synthesizing a wide range of enantioenriched atropisomers bearing multiple chiral elements. Therefore, the catalytic asymmetric synthesis of atropisomers bearing multiple chiral elements has become an emerging field. This review summarizes the rapid progress in this field and indicates challenges, thereby promoting this field to a new horizon.

CPA-catalyzed asymmetric domino thia-Michael/aldol reactions for simultaneous chiral center and axial chirality formation

A highly enantio- and diastereoselective domino thia-Michael/aldol reaction applying 5H-dibenzo[a,c][7]annulen-5-one as a Michael acceptor, catalyzed by a chiral phosphoric acid (CPA), has been developed. The bridged biaryl adduct contains multiple stereogenic centers in the bridging linkage as well as a thermodynamically controlled stereogenic axis. The energy difference between the two atropodiastereomers is about 9.1 kcal mol-1, which accounts for the observed excellent diastereoselectivity (>20 : 1).

Catalytic asymmetric synthesis of medium-sized bridged biaryls

Despite the persistent presence of medium-sized (seven- to nine-membered) scaffolds in natural products and biologically active molecules, their asymmetric syntheses have always been considered a formidable task; therefore, they have remained underdeveloped when compared to the enantioselective synthesis of five- and six-membered ring scaffolds. One important class of such medium-sized ring frameworks includes seven- to nine-membered biaryl bridged carbo- and heterocycles. These medium-ring-sized biaryl frameworks possess more configurational stability than the related smaller ring structures and are common features of valuable natural products, bioactive compounds, chiral catalysts, and molecular motors. Due to these exciting properties and broad applications, over the last few years, the catalytic enantioselective synthesis of medium-sized bridged biaryls has seen an upsurge. This highlight article describes the development of organocatalysed and transition-metal catalysed transformations for procuring seven-, eight-, and nine-membered bridged biaryls bearing a chiral axis/one or more asymmetric carbon centres.