Rhodium-catalyzed tunable oxidative cyclization toward the selective synthesis of α-pyrones and furans

The Rh^III-catalyzed tunable oxidative cyclization of readily availableN-tosylacrylamides and diazo compounds toward the selective synthesis of fully substituted furans and α-pyrones is presented.

Mechanism of the rhodium(iii)-catalyzed alkenylation reaction of N-phenoxyacetamide with styrene or N-tosylhydrazone: a computational study

A systematic density functional theory study has been conducted to examine the mechanisms involved in the rhodium(iii)-catalyzed alkenylation ofN-phenoxyacetamide with two different substrates (i.e., styrene andN-tosylhydrazone).

Mild metal-catalyzed C–H activation: examples and concepts

C–H Activation reactions that proceed under mild conditions are more attractive for applications in complex molecule synthesis. Mild C–H transformations reported since 2011 are reviewed and the different concepts and strategies that have enabled their mildness are discussed.

Rh(iii)-catalyzed redox-neutral annulation of azo and diazo compounds: one-step access to cinnolines

Cinnolines were synthesized in one step from azo and diazo compounds via a Rh(iii)-catalyzed redox-neutral C–H activation and C–N bond formation strategy.

Rh(iii)-catalyzed C–H activation/cyclization of oximes with alkenes for regioselective synthesis of isoquinolines

A Rh(iii)-catalyzed C–H activation/cyclization of oximes and alkenes for facile and regioselective access to isoquinolines has been developed.

Rhodium-catalyzed C–H activation of 3-(indolin-1-yl)-3-oxopropanenitriles with diazo compounds and tandem cyclization leading to hydrogenated azepino[3,2,1-hi]indoles

Rh(iii)-Catalyzed C–H activation of 3-(indolin-1-yl)-3-oxopropanenitriles with diazo compounds and tandem cyclization leading to seven-membered ring scaffolds has been developed.

Fe-Catalyzed Reductive Coupling of Unactivated Alkenes with β-Nitroalkenes

An Fe-catalyzed reductive coupling of unactivated alkenes with β-nitroalkenes has been developed. The reaction proceeds through a radical pathway, with β-nitroalkenes serving as the vinylating reagents and the nitro group being cleaved in the process. Therefore, this method provides a viable synthetic approach to valuable secondary- and tertiary-alkylated styrene derivatives. Furthermore, control experiments were conducted and a plausible mechanism is proposed.

All-Carbon [3+3] Oxidative Annulations of 1,3-Enynes by Rhodium(III)-Catalyzed C-H Functionalization and 1,4-Migration

1,3-Enynes containing allylic hydrogens cis to the alkyne function as three-carbon components in rhodium(III)-catalyzed, all-carbon [3+3] oxidative annulations to produce spirodialins. The proposed mechanism of these reactions involves the alkenyl-to-allyl 1,4-rhodium(III) migration.

Mechanistic Understanding of the Divergent Reactivity of Cyclopropenes in Rh(III)-Catalyzed C-H Activation/Cycloaddition Reactions of N-Phenoxyacetamide and N-Pivaloxybenzamide

Density functional theory calculations were conducted to develop a mechanistic understanding of the Rh(III)-catalyzed C-H activation/cycloaddition reactions of N-phenoxyacetamide and N-pivaloxybenzamide with cyclopropenes, and insights into the substrate-dependent chemoselectivity were provided. The results showed that the divergence originated from the different reactivity of the seven-membered rhodacycles from the insertion of cyclopropene into the Rh-C bond. In reactions of N-pivaloxybenzamide, such an intermediate undergoes the pivalate migration to form a cyclic Rh(V)-nitrenoid intermediate in a reaction that is easier than the opening of the three-membered ring by β-carbon elimination, leading finally to a tricyclic product with retention of the cyclopropane moiety by facile reductive elimination. While similar Rh(V)-nitrenoid species could also be possibly formed in Cp*Rh(III)-catalyzed reactions of N-phenoxyacetamide, the β-carbon elimination occurs more easily from the corresponding seven-membered rhodacycle intermediate and the subsequent O-N bond cleavage gives rise to an unexpected dearomatized (E)-6-alkenylcyclohexa-2,4-dienone intermediate. The E/Z isomerization of this intermediate is required for the final cyclization to 2H-chromene, and interesting metal-ligand cooperative catalysis with Rh(III) carboxylate was disclosed in the C═C double bond rotation process.

Pd(II)-catalyzed C-H functionalizations directed by distal weakly coordinating functional groups

Ortho-C(sp(2))-H olefination and acetoxylation of broadly useful synthetic building blocks phenylacetyl Weinreb amides, esters, and ketones are developed without installing an additional directing group. The interplay between the distal weak coordination and the ligand-acceleration is crucial for these reactions to proceed under mild conditions. The tolerance of longer distance between the target C-H bonds and the directing functional groups also allows for the functionalizations of more distal C-H bonds in hydrocinnamoyl ketones, Weinreb amides, and biphenyl Weinreb amides. Mechanistically, the coordination of these carbonyl groups and the bisdentate amino acid ligand with Pd(II) centers provides further evidence for our early hypothesis that the carbonyl groups of the potassium carboxylate are responsible for the directed C-H activation of carboxylic acids.

Synthesis of quinolinones with palladium-catalyzed oxidative annulation between acrylamides and arynes

An unprecedented palladium-catalyzed oxidative annulation of acrylamides with benzyne precursors has been successfully developed. By using this mild "N-H activation/Heck reaction" method, a wide variety of quinolinones were conveniently prepared in one step with high efficiency.

Rhodium-catalyzed C-H functionalization-based approach to eight-membered lactams

A Rh(iii) catalyzed formal [4 + 2 + 2] cyclization of N-pivaloyloxybenzamides 1 with 1,6-allene-enes 2 by C-H functionalization is reported. The reactions occur at room temperature and are compatible with air and moisture with a tolerance of many synthetically useful functional groups. The follow-up modifications of the products have been demonstrated. After careful mechanistic studies and DFT calculation, a reaction mechanism was proposed.

Rhodium-catalyzed C-H activation of phenacyl ammonium salts assisted by an oxidizing C-N bond: a combination of experimental and theoretical studies

Rh(III)-catalyzed C-H activation assisted by an oxidizing directing group has evolved to a mild and redox-economic strategy for the construction of heterocycles. Despite the success, these coupling systems are currently limited to cleavage of an oxidizing N-O or N-N bond. Cleavage of an oxidizing C-N bond, which allows for complementary carbocycle synthesis, is unprecedented. In this article, α-ammonium acetophenones with an oxidizing C-N bond have been designed as substrates for Rh(III)-catalyzed C-H activation under redox-neutral conditions. The coupling with α-diazo esters afforded benzocyclopentanones, and the coupling with unactivated alkenes such as styrenes and aliphatic olefins gave ortho-olefinated acetophenoes. In both systems the reactions proceeded with a broad scope, high efficiency, and functional group tolerance. Moreover, efficient one-pot coupling of diazo esters has been realized starting from α-bromoacetophenones and triethylamine. The reaction mechanism for the coupling with diazo esters has been studied by a combination of experimental and theoretical methods. In particular, three distinct mechanistic pathways have been scrutinized by DFT studies, which revealed that the C-H activation occurs via a C-bound enolate-assisted concerted metalation-deprotonation mechanism and is rate-limiting. In subsequent C-C formation steps, the lowest energy pathway involves two rhodium carbene species as key intermediates.

Regioselective synthesis of multisubstituted isoquinolones and pyridones via Rh(iii)-catalyzed annulation reactions

A mild and efficient Rh(iii)-catalyzed regioselective synthesis of isoquinolones and pyridones from N-methoxybenzamide or N-methoxymethacrylamide and diazo compounds has been developed, through tandem C–H activation, cyclization, and condensation.

One-pot cascade synthesis of N-methoxyisoquinolinediones via Rh(iii)-catalyzed carbenoid insertion C–H activation/cyclization

A mild and efficient method for one-pot synthesis of N-methoxyisoquinolinediones via Rh(iii)-catalyzed carbenoid insertion C–H activation/cyclization has been developed.

Transition metal-catalyzed C–H functionalization of N-oxyenamine internal oxidants

The N-oxyenamine internal oxidant gives more chance to investigate the C–H bond activation under mild reaction conditions.

C–H bond functionalization based on metal carbene migratory insertion

C–H bond activation has been merged with carbene coupling to furnish a series of novel synthetic methodologies.

Direct C–H alkylation and indole formation of anilines with diazo compounds under rhodium catalysis

The rhodium(iii)-catalyzed direct functionalization of aniline C–H bonds with α-diazo compounds for the preparation of ortho-alkylated anilines and highly substituted indoles is described.

Cp*Rh(iii) and Cp*Ir(iii)-catalysed redox-neutral C–H arylation with quinone diazides: quick and facile synthesis of arylated phenols

Cp*Rh(iii)- and Cp*Ir(iii)-catalysed direct C–H arylation with quinone diazides provides a facile and redox-neutral access to arylated phenols.

Rh(iii)-catalyzed C–H activation/cyclization of benzamides and diazo compounds to form isocoumarins and α-pyrones

Rhodium-catalyzed intermolecular cyclization of benzamides and diazo compounds via C–H activation has been achieved to construct C–C/C–O bonds for the first time.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

Rh(iii)-catalyzed and alcohol-involved carbenoid C–H insertion into N-phenoxyacetamides using α-diazomalonates

Here a new, mild and efficient Rh(iii)-catalyzed and alcohol-involved carbenoid insertion (ortho-alkylation) intoN-phenoxyacetamides using α-diazomalonates has been developed.