Rh(III)-catalyzed C–H alkylation of 2-arylbenzothiazoles with α-diazo esters

Rh(III)-Catalyzed C7-Alkylation of Isatogens with Malonic Acid Diazoesters

Rh(III)-catalyzed C7-alkylation of isatogens (indolin-3-one N-oxides) with malonic acid diazoesters has been developed. This strategy utilizes oxygen anion on the N-oxide group of isatogens as a directing group and successfully achieves the synthesis of a series of C7-alkylated isatogens with moderate to good yields (48-86% yields). Moreover, the N-oxides of isatogens can not only serve as the simple directing group for C7-H bond cleavage but also be deoxidized for easy removal.

Aromatic C-H Methylation and Other Functionalizations via the Rh(III)-Catalyzed Migratory Insertion of Bis(phenylsulfonyl)carbene and Subsequent Transformations

The Rh(III)-catalyzed migratory insertion of bis(phenylsulfonyl)carbene into aromatic C-H bonds has been developed. A variety of bis(phenylsulfonyl)methyl derivatives were prepared with good yields under mild conditions. The methylated products were readily obtained after reductive desulfonylation. Furthermore, the diverse transformations of bis(phenylsulfonyl)methyl to trideuteriomethyl, aldehyde, and other functional groups were demonstrated.

Catalytic synthesis of functionalized amidines via cobalt-carbene radical coupling with isocyanides and amines

An atom- and step-economic multi-component cobalt-catalyzed synthesis of amidines has been reported by using amines, isocyanides, and diazo compounds as carbene sources.

Recent Advances in the Synthesis and Applications of 2-Arylbenzothiazoles

This review firstly covers the applications of 2-arylbenzothiazoles as amyloid imaging agents, antitumor agents, and organic luminescent materials. Then we review the recent advances in the synthesis of 2-arylbenzothiazole derivatives. On the one hand, we introduce the approaches for construction of the 2-arylbenzothiazole core, including the following categories: (i) classic condensation of 2-aminothiophenols, (ii) direct arylation of benzothiazoles, (iii) intramolecular cyclization of thiobenzanilides, and (iv) tandem cyclization of anilines/ nitroarenes­ with elemental sulfur or sulfides. On the other hand, the transition-metal-catalyzed direct C–H functionalizations of 2-aryl­benzothiazoles are also involved in this review.

1 Introduction

2 Applications of 2-Arylbenzothiazoles

3 Construction of the 2-Arylbenzothiazole Core

4 Synthesis 2-Arylbenzothiazoles via Direct C–H Functionalization

5 Conclusion

[2 + 1 + 1] Assembly of spiro β-lactams by Rh(ii)-catalyzed reaction of diazocarbonyl compounds with azirines/isoxazoles

A domino synthesis of dispiro-fused N-vinyl β-lactams from diazo-Meldrum's acid and 2H-azirines or 5-alkoxyisoxazoles via the "2-azabuta-1,3-diene formation/Staudinger ketene-imine cycloaddition" sequence is described. The Rh2(Piv)4-catalyzed formation of the 2-azabuta-1,3-diene intermediates in the first stage of the reaction sequence proceeds via addition of the rhodium carbenoid to the azirines/isoxazoles and provides the first example of the generation of iminium-type ylides from diazo-Meldrum's acid. This methodology was extended to monospiro-β-lactams, which were synthesized in two steps using acyclic α-diazocarbonyl compounds in the stage of the formation of 2-azabuta-1,3-dienes. The method allows for the rapid assemblage of the carbon part of the azetidin-2-one system from diazo compounds only and affords spiro- and dispiro-β-lactams in moderate yields. A bromine atom in the 2-bromoalkenyl moiety of the synthesized β-lactams can be easily substituted by hydrogen under catalytic hydrogenation conditions or by 2-pyridyl-substituent via the Stille cross-coupling reaction.

Rhodium(iii)-catalyzed CF3-carbenoid C–H functionalization of 6-arylpurines

An expedient route to access a new family of fluorine-containing purine derivatives via chelation-controlled rhodium(iii)-catalyzed carbenoid C–H functionalization has been developed.

Rh(iii)-Catalyzed synthesis of pyrazolo[1,2-a]cinnolines from pyrazolidinones and diazo compounds

Pyrazolo[1,2-a]cinnolines were achieved via a rhodium(iii)-catalyzed redox-neutral annulation procedure, exhibiting good regioselectivity and high functional group tolerability.

Rh(III)-Catalyzed C-H Activation/Intramolecular Cyclization: Access to N-Acyl-2,3-dihydro-1H-carbazol-4(9H)-ones from Cyclic 2-Diazo-1,3-diketones and N-Arylamides

A Rh(III)-catalyzed C-H activation/cyclization cascade reaction is described. The reaction involves cyclic 2-diazo-1,3-diketones and N-arylamides, and it proceeds via an intermolecular C-C bond formation and subsequent intramolecular C-N bond formation. A variety of N-acyl-2,3-dihydro-1H-carbazol-4(9H)-ones were obtained under mild conditions in good to excellent yields (65-90%). Key features of this strategy include high-efficiency, operational simplicity, scalability, and broad functional-group tolerance. In addition, H2O and N2 are the only byproducts. Carbazole derivatives with free NH groups can be easily obtained through N-deprotection reactions.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

Rh(III)-catalyzed oxidative ortho-C–H alkylation of 2,4-diarylquinazoline with potassium alkyltrifluoroborates

Alkyltrifluoroborates were used for Rh(III)-catalyzed ortho-alkylation of 2,4-disubstituted quinazoline via C–H bond activation. The reaction proceeded well with a broad substrate scope, providing a direct way to access high functional quinazoline core structure derivatives in yields up to 95%.

Rh(iii)-catalyzed sequential C–H activation and annulation: access to N-fused heterocycles from arylazoles and α-diazocarbonyl compounds

Valuable N-fused heterocycles were successfully obtained via Rh(iii)-catalyzed sequential C–H activation and annulation.

Synthesis of isoquinolines via Rh-catalyzed C–H activation/C–N cyclization with diazodiesters or diazoketoesters as a C2 source

Synthesis of isoquinolines based on efficient C–C and C–N bond formation through Rh(iii)-catalyzed C–H functionalization and subsequent intramolecular cyclization is reported. Diazodiesters serving as a C₂ source in the newly formed heterocycles are first demonstrated.

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.

Ir(iii)-catalyzed synthesis of isoquinolines from benzimidates and α-diazocarbonyl compounds

We report herein a tandem Ir(iii)-catalyzed C–H activation and annulation reactions for the synthesis of isoquinolines. This novel method affords an alternative strategy for the construction of diverse and useful isoquinoline derivatives.

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.