Organoboron Initiated Rh-Catalyzed Asymmetric Cascade Reactions: A Subtle Switch in Regioselectivity Leading to Chiral 3-Benzazepine Derivatives

Synthesis of Tetrasubstituted Alkenes by Rhodium-Catalyzed Regioselective Cyano Transfer

We describe herein a novel, general, and robust approach to structurally diversified alkenyl nitriles through a Rh-catalyzed cyano transfer reaction between alkynyl-malononitrile derivatives and aryl/alkenyl boronic acids. This reaction exhibits high chemo- and regioselectivity and a broad substrate scope. The tetrasubstituted alkenyl dinitriles (34 examples, average 58% yield) are obtained through substrate tuning and ligand control.

Recent advances in Rh(I)-catalyzed enantioselective C-H functionalization

Chiral carbon-carbon (C-C) and carbon-heteroatom (C-X) bonds are pervasive and very essential in natural products, bioactive molecules, and functional materials, and their catalytic construction has emerged as one of the hottest research fields in synthetic organic chemistry. The last decade has witnessed vigorous progress in Rh(I)-catalyzed asymmetric C-H functionalization as a complement to Rh(II) and Rh(III) catalysis. This review aims to provide the most comprehensive and up-to-date summary covering the recent advances in Rh(I)-catalyzed C-H activation for asymmetric functionalization. In addition to the development of diverse reactions, chiral ligand design and mechanistic investigation (inner-sphere mechanism, outer-sphere mechanism, and 1,4-Rh migration) will also be highlighted.

Relay Zn(ii)- and Au(i)-catalyzed aziridination/cyclization/ring expansion sequence to form 3-benzazepine derivatives

The synthesis of 3H-benzo[d]azepine-2-carboxylates from 2-alkynylphenyl aldimines and α-diazo esters using Zn(ii) and Au(i) catalysts is described.

One-Pot Synthesis of 2,3-Disubstituted Indanone Derivatives in Water under Exogenous Ligand-Free and Mild Conditions

Diverse 2,3-substituted indanones are accessed in an efficient and robust protocol by a rhodium-catalyzed tandem carborhodium/cyclization and intramolecular proton shift pathway. The reaction is compatible with a broad range of functional internal acetylenes, especially for natural and functionalized alkynes derivatives, affording the desired indanones in good to excellent yields. Remarkably, this reaction features very mild and sustainable conditions using water as the sole solvent and without exogenous ligands. Control studies support that indanone is formed through the intramolecular proton transfer process from the key intermediate indenol.

Catalyst-controlled cycloisomerization/[4+3] cycloaddition sequence to construct 2,3-furan-fused dihydroazepines and 2,3-pyrrole-fused dihydrooxepines

A novel catalyst-controlled cycloisomerization/[4+3]cycloaddition sequence of readily available acyclic enyne-amides and crotonate-derived sulfur ylides is reported. This strategy enables the rapid and efficient construction of a series of bicyclic 2,3-furan-fused...

Pd/LA-catalyzed decarboxylation enabled exclusive [5 + 2] annulation toward N-aryl azepanes and DFT insights

A practical approach towards the synthesis of non-fused N-aryl azepane derivatives with diversity is described. DFT calculations revealed the origins of this unusual exclusive [5 + 2] rather than empirical [3 + 2] annulation process.

Copper-catalyzed tandem cis-carbometallation/cyclization of imine-ynamides with arylboronic acids

An efficient copper-catalyzed tandem regioselective cis-carbometallation/cyclization of imine-ynamides with arylboronic acids has been developed. This method leads to a facile and practical synthesis of valuable 2,3-disubstituted indolines in moderate to excellent yields and features a broad substrate scope and wide functional group tolerance. Other significant features of this protocol include the use of readily available starting materials, high flexibility, simple procedure and mild reaction conditions.

Construction of 1-Tetralols Bearing Two Contiguous Quaternary Chiral Centers through a Rhodium-Catalyzed Enantioselective Desymmetrization Cascade Reaction

A novel and efficient access to polyfunctionnalized chiral 1-tetralols, bearing two contiguous quaternary carbon stereocenters, has been developed from various and easily accessible alkynyl-1,3-diketones, through a cascade process including a regioselective alkyne insertion, a 1,4-Rh shift, and a nucleophilic addition step via the desymmetrization of the 1,3-diketone moiety thanks to an appropriate rhodium-chiral diene complex in the presence of arylboronic acids.

Catalytic enantioselective arylative cyclizations of alkynyl 1,3-diketones by 1,4-rhodium(i) migration

The enantioselective synthesis of densely functionalized polycarbocycles by the rhodium(i)-catalyzed reaction of arylboronic acids with 1,3-diketones is described. The key step in these desymmetrizing domino addition–cyclization reactions is an alkenyl-to-aryl 1,4-Rh(i) migration, which enables arylboronic acids to function effectively as 1,2-dimetalloarene surrogates.

The enantioselective synthesis of densely functionalized polycarbocycles by the rhodium(i)-catalyzed reaction of arylboronic acids with alkynyl 1,3-diketones is described. The key step in these reactions is an alkenyl-to-aryl 1,4-Rh(i) migration..

From Tetrahydrofurans to Tetrahydrobenzo[ d]oxepines via a Regioselective Control of Alkyne Insertion in Rhodium-Catalyzed Arylative Cyclization

The formation of chiral 5- and 7-membered tetrahydrofurans and tetrahydrobenzo[ d]oxepines is achieved via arylative cyclization of simple O-tethered alkyne-enoates in the presence of arylboronic acids and chiral dienes-rhodium catalyst under mild conditions. Access to such structures was achieved via a simple switch in the regioselectivity of the alkyne insertion thanks to a proper choice of the alkyne substituent.

Rhodium-catalyzed arylative cyclization of alkynyl malonates by 1,4-rhodium(i) migration

The synthesis of functionalized 1-tetralones by the rhodium(i)-catalyzed reaction of alkynyl malonates with arylboronic acids is described.

Access to chiral cyano-containing five-membered rings through enantioconvergent rhodium-catalyzed cascade cyclization of a diastereoisomeric E/Z mixture of 1,6-enynes

In contrast to the intermolecular rhodium-catalyzed asymmetric 1,4-addition of organometallic reagents to activated alkenes, the asymmetric arylative cyclization of a diastereoisomeric E/Z mixture of 1,6-enynes afforded only one major enantiomer.

Synthesis of Diversely Functionalized 2 H-Chromenes through Pd-Catalyzed Cascade Reactions of 1,1-Dibromoolefin Derivatives with Arylboronic Acids

In this work, an unprecedented synthesis of (2 H-chromen-2-ylidene)acetates and (2 H-chromen-2-ylidene)ethanones with controlled stereoselectivity via Pd-catalyzed cascade reactions of 3-(2-(2,2-dibromovinyl)phenoxy)acrylates or 3-(2-(2,2-dibromovinyl)phenoxy)enones with aryl boronic acids has been established. This protocol combines two C-C bond forming reactions (an intermolecular Suzuki coupling followed by an intramolecular Heck coupling) in one pot under the catalysis of the same catalyst. Compared with literature methods for the preparation of 2 H-chromene derivatives, it has advantages such as easily obtainable or commercially available substrates, diverse substitution pattern of products, simple procedure, and excellent stereoselectivity. Interestingly, this cascade reaction could distinguish the subtle difference of the electron-withdrawing capacity and the size of various functional groups and thus resulted in a different chemoselectivity. In addition, the utility of the (2 H-chromen-2-ylidene)acetate thus obtained was showcased by its facile transformation into the synthetically and photophysically significant 3 H-xanthen-3-one derivative.

Substitution-Controlled Selective Formation of Hexahydrobenz[ e]isoindoles and 3-Benzazepines via In(OTf)3-Catalyzed Tandem Annulations

A dramatic N-substituent controlled tandem annulation of 2-(2-(2-bromoethyl)phenyl)-1-sulfonylaziridines with 1,3-dicarbonyl compounds has been developed. When the N-substituent was a 4-methylbenzenesulfonyl group (Ts), sequential ring opening of aziridines, nucleophilic substitution, and lactamization took place to provide a series of hexahydrobenz[ e]isoindole compounds in good yields with good diastereoselectivities. By contrast, 3-benzazepine compounds were afforded in good yields via ring opening of aziridines and nucleophilic substitution when the N-substituent was the 4-nitrobenzenesulfonyl group (Ns).

Modular Access to Azepines by Directed Carbonylative C-C Bond Activation of Aminocyclopropanes

A modular Rh-catalyzed entry to azepines is outlined. Under a CO atmosphere, protecting group directed C–C bond activation of aminocyclopropanes provides rhodacyclopentanones. These intermediates are effective for intramolecular C–H metalation of either an N-aryl or N-vinyl unit en route to azepine ring systems. Thus, byproduct-free heterocyclizations are enabled by sequential C–C activation and C–H functionalization steps.