Iridium(III)-Catalyzed Regioselective Carbenoid Insertion C-H Alkylation by α-Diazotized Meldrum's Acid

Rh(III)- or Ru(II)-Catalyzed C-H Annulation with Vinylene Carbonate and an Unexpected Aerobic Oxidation/Deprotection Cascade to Yield Cinnolin-4(1H)-ones

Transition metal-catalyzed C-H annulation reactions have been extensively utilized for the synthesis of cinnolines, especially the N-protected ones; however, none of them can yield cinnolin-4(1H)-ones, a significant class of bioactive skeletons. Herein, we disclose one-pot access to cinnolin-4(1H)-ones through Rh(III)- or Ru(II)-catalyzed C-H activation/annulation of N-aryl cyclic hydrazides with vinylene carbonate, followed by an O2/K2CO3-promoted aerobic oxidation/deprotection cascade. The π-conjugation of the directing groups plays a crucial role in facilitating this transformation. Notably, seven-membered enolic Rh species IMC is characterized via electrospray ionization mass spectroscopy for the first time, which, along with systematic control experiments, provides compelling evidence for the mechanistic pathway encompassing alkenyl insertion, β-oxygen elimination, protonation, and dehydration.

Iridium(III)-Catalyzed C-H Cyclization of Sulfoximines with Diazo Meldrum's Acids for the Synthesis of Cyclic Sulfoximines

Iridium(III)-catalyzed C-H cyclization of sulfoximines with diazo Meldrum's acid provided cyclic sulfoximines with a carbonyl group in good to excellent yields. These compounds were easily converted into unsubstituted and arylated sulfoximines. Moreover, the vinyl triflates obtained from the cyclic sulfoximines underwent palladium(II)-catalyzed cross-coupling reactions with a variety of aryl, arylalkynyl, and heteroatom (N and S) nucleophiles, affording a wide range of monosubstituted sulfoximines in high yields.

Free Amine-Directed Ru(II)-Catalyzed Redox-Neutral [4 + 2] C-H Activation/Annulation of Benzylamines with Sulfoxonium Ylides

An external oxidant free Ru(II)-catalyzed C-H functionalization/annulation of primary benzylamines with sulfoxonium ylides has been developed for the synthesis of isoquinolines. The reaction utilizes free amine as a directing group, which is generally considered to be a poor directing group. This work presents the first example of Ru-catalyzed C-H functionalization of benzylamines under redox-neutral conditions. The detection of the amine-directed ruthenacyclic intermediate using high-resolution mass spectrometry corroborated the involvement of free amine as a directing group.

Rh(III)-Catalyzed ortho C-H functionalization of aromatic amides with bis(phenylsulfonyl)diazomethane and α-diazosulfones

A Rh(III)-catalyzed migratory insertion of bis(phenylsulfonyl) carbene and α-sulfonyl carbenes into ortho C-H bonds of aryl amides has been developed. The products were obtained with moderate to excellent yields under mild reaction conditions. A reaction mechanism was proposed based on the control experiments and previous studies. Diverse desulfonylation transformations of the products were achieved.

Water-Mediated ortho-Carboxymethylation of Aryl Ketones under Ir(III)-Catalytic Conditions: Step Economy Total Synthesis of Cytosporones A-C

An expeditious Ir(III)-catalyzed carboxymethylation of aryl ketone with diazotized Meldrum's acid has been developed in aqueous medium. Flavanone and chromanone were also found to be facile substrates with the developed catalytic system. Mechanistic studies revealed the active catalytic species and the role of water in the reaction process as hydroxy and proton sources. Employing the developed method, total synthesis of cytosporone A was achieved in two steps and that of cytosporones B-C was achieved in three steps starting from resorcinol.

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.

Rhodium-catalysed direct formylmethylation using vinylene carbonate and sequential dehydrogenative esterification

A rhodium-catalysed direct formylmethylation adopting vinylene carbonate as an ethynol equivalent is reported. The developed catalytic system is further utilised for the oxidant-free production of esters with the liberation of hydrogen gas. Some control experiments are conducted to elucidate the reaction mechanism.

Tandem Carbenoid C-H Functionalization/Conia-ene Cyclization of N-Propargyl Indoles Generates Pyrroloindoles under Cooperative Rh(II)/Zn(II) Catalysis

The decomposition of diazodicarbonyl compounds in the presence of various metal catalysts has become a reliable method for the functionalization of indoles via carbenoid intermediates. Exploiting the nucleophilic reactivity of the in situ generated malonic ester product formed, we herein report a tandem C-H functionalization/Conia-ene cyclization of N-alkyne tethered indoles. This double functionalization of diazodicarbonyls generates a range of pyrrolo[1,2-a]-, pyrido[1,2-a]-, and azepino[1,2-a]indole products with good synthetic efficiency.

[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.

Water-mediated C–H activation of arenes with secure carbene precursors: the reaction and its application

A water-mediated C–H activation using sulfoxonium ylides is reported, providing a general, green and step-economic approach to construct a C–C bond and varieties of useful N-heterocycle scaffolds.

Ir(iii)-Catalyzed [4 + 2] cyclization of azobenzene and diazotized Meldrum's acid for the synthesis of cinnolin-3(2H)-one

The first report on Ir(iii)-catalyzed C–H alkylation/cyclization of azobenzene with diazotized Meldrum's acid was developed for the synthesis of cinnoline-3(2H)-one-4-carboxylic acid and its ester derivative under mild conditions.

Catalyst-controlled selective mono-/dialkylation of 2-aryl-4(3H)-quinazolinones

Catalyst-controlled selective mono-/dialkylation of 2-aryl-4(3H)-quinazolinones with α-diazotized Meldrum's acid has been achieved successfully via a metal carbene migratory insertion process.

Construction of pyrazolone analogues via rhodium-catalyzed C–H activation from pyrazolones and non-activated free allyl alcohols

Highly efficient rhodium(iii) catalysis was developed for obtaining structurally divergent pyrazolone analogues from pyrazolones and non-activated free allyl alcohols.

Rh-Catalyzed C–H bond alkylation of indoles with α,α-difluorovinyl tosylate via indolyl group migration

An unprecedented C–H alkylation of indoles was achieved with α,α-difluorovinyl tosylate through an indolyl group shift process enabled by fluorine substituents.

Divergent synthesis of α-aryl ketones/esters via rhodium-catalyzed selective deesterification and decarbonylation of diazo compounds

A rhodium-catalyzed selective deesterification, decarbonylation and dual C–H activation of diazo compounds is presented.

Cp*Ir(iii)-catalyzed C–H/N–H functionalization of sulfoximines for the synthesis of 1,2-benzothiazines at room temperature

The first Cp*Ir(iii)-catalyzed C–H/N–H bond functionalization of sulfoximines with α-diazocarbonyl compounds has been developed for the synthesis of 1,2-benzothiazines under redox-neutral conditions at room temperature.

Iron(ii)-catalyzed C-2 cyanomethylation of indoles and pyrroles via direct oxidative cross-dehydrogenative coupling with acetonitrile derivatives

A novel and efficient approach for the C(sp²)–H/C(sp³)–H oxidative coupling of indoles and pyrroles with acetonitrile derivatives was reported by using the Fe(ii) complex.

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.

One-pot synthesis of 2,3-difunctionalized indoles via Rh(iii)-catalyzed carbenoid insertion C–H activation/cyclization

A new and versatile Rh(iii)-catalyzed carbenoid insertion C–H activation/cyclization for one-pot synthesis of 2,3-difunctionalized indoles has been developed.

An Ir(iii)-catalyzed aryl C–H bond carbenoid functionalization cascade: access to 1,3-dihydroindol-2-ones

An Ir(iii)-catalyzed relay aryl C–H bond carbenoid insertion cascade of N-aryl-2-pyridinamines with diazo Meldrum's acid has been developed.