A diastereoselective synthesis of functionalized bis-spirorhodanine-linked cyclopentanes via C(sp3)–H activation

A diastereoselective synthesis of bis-spirorhodanine-linked cyclopentane derivatives via the [2 + 2+1] cycloaddition reaction between alkyl (Z)-2-(3-alkyl-4-oxo-2-thioxothiazolidin-5-ylidene)acetates (alkylidenerhodanines) and azomethine ylides, prepared in situ from iodine mediated reaction of 2-methylquinoline and pyridine in the presence of base, has been developed. The structure of a typical product was confirmed by X-ray crystallography.     

Rhodium(III) catalyzed synthesis of isoquinolone fused azabicycles through C–H activation of N-pivaloyloxy benzamides

Herein we describe an efficient one pot strategy toward highly functionalized isoquinolone fused azabicycles having great synthetic potential via C–H activation of N-pivaloyloxy benzamides under very mild conditions. The reaction is accomplished at room temperature within one hour in good to excellent yields and is found to be compatible with a range of diazabicyclic olefins and benzamides. The present strategy offers an easy route for the synthesis of biologically relevant compounds which possess multiple points for divergent synthesis. N–N bond cleavage of synthesized compounds may enable their significant role as effective precursors for the preparation of diaminocyclopentane fused isoquinolones.     

Synthesis of substituted β-carbolines via gold(III)-catalyzed cycloisomerization of N-propargylamides

Indole-substituted N-propargylamides undergo a gold(III)-catalyzed cyclization to give oxazoles or β-carbolinones, depending on the substitution pattern at the amide nitrogen. Secondary amides furnished oxazoles via a 5-exo-dig cyclization, while tertiary indole-2-carboxamides cycloisomerized to give 2,9-dihydro-β-carbolin-1-ones upon treatment with catalytic amounts of gold(III) chloride. An optimized procedure was developed to prepare several new N-benzyl-β-carbolinones as well as the corresponding β-carbolines, which are of interest as core structures found in various natural products such as the harman, ervolanine, and lavendamycin class of alkaloids.     

Rh(III)-catalyzed C–H acylmethylation of 2H-indazoles with sulfoxonium ylides

An efficient Cp*Rh(III)-catalyzed direct acylmethylation of 2H-indazoles with sulfoxonium ylides has been realized under air atmosphere via chelation-assisted strategy. This protocol enables a regioselective access to a variety of ortho-acylmethylated 2-phenylindazole derivatives in moderate to good yield, which has the advantages of broad substrate scope, good functional group tolerance, and operational convenience. The H/D exchange experiment reveals that a reversible cleavage of C–H bond might not be the rate-limiting step in this transformation.     

Orthoamides by selective borohydride reduction of N,N′,N″-triacyl- and N,N′,N″-tri(alkoxycarbonyl)-guanidines

N,N′,N″-Triacylguanidines and N,N′,N″-tri(alkoxycarbonyl)guanidines were prepared and reduced with borohydride salts in a mixture of tetrahydrofuran and acetic acid to give triacyl and tri(alkoxycarbonyl) orthoamides in yields of 40–85%. However, similar reduction of N,N′,N″-tri(t-butoxycarbonyl)guanidine did not give orthoamide but the aminal di(t-butyl) methylenedicarbamate.     

Mechanism of rhodium(III)-catalyzed formal C(sp3)H activation/spiroannulation of α-arylidene pyrazolones with alkynes: A computational study

DFT calculations were performed to investigate the rhodium-catalyzed formal C(sp³)-H activation/ spiroannulation of α-arylidene pyrazolones with alkynes. The calculations indicate that the spiroannulation through the proposed C-C reductive elimination is kinetically unfeasible. Instead, the C-C coupling from the eight-membered rhodacycle was proposed to account for the experimental results     

Rhodium(III)-catalyzed C–H functionalization of C-alkenyl azoles with sulfoxonium ylides for the synthesis of bridgehead N-fused [5,6]-bicyclic heterocycles

The synthesis of bridgehead N-fused [5,6]-bicyclic heterocycles via rhodium(III)-catalyzed C–H functionalization of C-alkenyl azoles with sulfoxonium ylides is disclosed. Reactions proceeded in good to high yields for a range of aryl, heteroaryl and alkyl sulfoxonium ylides. In addition, 2-alkenyl imidazoles with different substitution patterns as well as C-alkenyl triazoles were effective inputs. The reaction could also be performed under straightforward bench top conditions.     

Elemental iodine mediated synthesis of thiadiazole-based dithiafulvalene donors via C(sp2)–S formation

A series of thiadiazole-based dithiafulvalene (DTF) derivatives has been synthesized in moderate yields via iodine-mediated oxidative vinylic C(sp²)–H sulfenylation with mercapto-thiadiazoles. The formation of C(sp²)–S bond was confirmed and characterized by NMR and single crystal X-ray diffraction studies. This new protocol is simple and effective for preparation DTF containing thiadiazole group.     

Synthesis of 2-(N-arylimino-κN-methyl)pyrrolide-κN complexes of nickel

2-(N-aryliminomethyl)pyrrole precursors (2,6-R₂-C₆H₃-NCH-2-C₄H₃NH) (R = Me, IH; R = ⁱPr, IIH) were prepared and transformed into their corresponding sodium salts (Na⁺I⁻ and Na⁺II⁻) by treatment with NaH. Both salts readily react with [NiBr₂(DME)] (DME = 1,2-dimethoxyethane) to give the respective bis{2-(N-arylimino-κN-methyl)pyrrolide-κN}nickel(II) complexes (1, 2) in almost quantitative yields. The oxidative addition of IH to [Ni(COD)₂] (COD = 1,5-cyclooctadiene) results in the formation of 3, which is a mono(iminomethylpyrrolide)-η³-(cyclic-allyl)-type organonickel(II) complex. The crystal structure of compound 1 has been established by X-ray diffraction studies.     

Microwave-promoted total synthesis of N-(α-hydroxybenzyl)formamides using DMSO/H2O under neutral conditions

A total synthesis route toward N-(α-hydroxybenzyl)formamides by microwave-assisted reaction of dichloroaziridines and aqueous dimethyl sulfoxide is described. The corresponding products were obtained in excellent yields with reduced reaction times. The obtained formamides were characterized by various techniques such as Infra red (IR), Nuclear Magnetic Resonance (NMR) and mass spectroscopy data.     

Rhodium(III)-Catalyzed C−H/N−H Functionalization with Hydrogen Evolution

A rhodium(III)-catalyzed C−H/N−H bond functionalization of benzimidates with α-chloroaldehydes to afford isoquinolin-3-ol derivatives is reported. No external oxidants are needed in this process, and interestingly, evolution of hydrogen gas is observed.     

Site-selective C–H nitration of N-aryl-7-azaindoles under palladium(II) catalysis

The site-selective C–H nitration reaction of 7-azaindoles with t-butyl nitrite under palladium catalysis is described. This protocol provides an efficient method for the construction of ortho-nitrated N-aryl-7-azaindoles with excellent site-selectivity and functional group compatibility. The formed 7-azaindole derivatives can be readily transformed into 7-azaindoles containing an aniline functional group under palladium-catalyzed hydrogenation conditions.     

Synthesis of tetrahydroindolones and tetrahydrocarbazolones via palladium catalyzed C–H activation

The treatment of bromo homoallyl pyrrolyl/indolyl ketone derivatives with Pd(OAc)₂ in the presence of PPh₃ and Cs₂CO₃ in DMF resulted in the formation of tetrahydroindolones and tetrahydrocarbazolones in moderate to good isolated yields.     

Au(III)-catalyzed tandem amination-hydration of alkynes: synthesis of α-(N-2-pyridonyl)ketones

A new Au(III)-catalyzed tandem amination-hydration reaction has been discovered, leading to the formation of α-(N-2-pyridonyl)ketones and heterocyclic analogues in good to excellent yields (14 examples, 48-90%). This reaction demonstrates the unusual use of a heterocyclic sp(2) nitrogen nucleophile in a gold-catalyzed 6-endo-dig cyclization. The tandem process allows rapid access to α-(N-2-pyridonyl)ketones, making them a convenient building block for the synthesis of more complex N-alkyl pyridone targets.     

Ru-catalyzed direct C–H amidation of 2-arylbenzo[d]thiazoles with sulfonyl azides

Ru-catalyzed direct C–H amidation of 2-arylbenzo[d]thiazoles was developed using sulfonyl azides as the amino source under no external oxidants and free-base conditions to release N₂ gas as the single byproduct. The present protocol shows good functional group tolerance and high regioselectivity, providing various structurally versatile amidated 2-arylbenzothiazoles with potential biological and therapeutic activities in moderate to good yields.     

Palladium-Catalyzed C−H Bond Arylation of Cyclometalated Difluorinated 2-Arylisoquinolinyl Iridium(III) Complexes

The utility of C−H bond functionalization of metalated ligands for the elaboration of aryl-functionalized difluorinated-1-arylisoquinolinyl Ir(III) complexes has been explored. Bis[(3,5-difluorophenyl)isoquinolinyl](2,2,6,6-tetramethyl-3,5-heptanedionato) iridium(III) undergoes Pd-catalyzed C−H bond arylation with aryl bromides. The reaction regioselectively occurred at the C−H bond flanked by the two fluorine atoms of the difluoroaryl unit, and on both cyclometalated ligands. This post-functionalization gives a straightforward access to modified complexes in only one manipulation and allows to introduce thermally sensitive functional groups, such as trifluoromethyl, nitrile, benzoyl, or ester. The X-ray crystallography, photophysical, and electrochemical properties of the diarylated complexes were investigated. Whatever the nature of the incorporated substituted aryl groups is, all obtained complexes emit red phosphorescence (622–632 nm) with similar lifetimes (1.9–2 μs).     

Direct synthesis of benzoxazinones via Cp*Co(III)-catalyzed C–H activation and annulation of sulfoxonium ylides with dioxazolones

A highly novel and direct synthesis of benzoxazinones was developed via Cp*Co(III)-catalyzed C–H activation and [3 + 3] annulation between sulfoxonium ylides and dioxazolones. The reaction is conducted under base-free conditions and tolerates various functional groups. Starting from diverse readily available sulfoxonium ylides and dioxazolones, a variety of benzoxazinones could be synthesized in one step in 32%-75% yields.     

Oxidative C(Sp)–H activation and C–N cleavage of N-methyl amines under transition-metal-free condition for synthesis of methylene-bridged bis-1,3-diketones

A transition-metal-free oxidative methylenation reaction was developed. Methylene-bridged bis-1,3-dicarbonyl compounds were synthesized by oxidative C(Sp³)–H activation and C–N cleavage of N-methyl amines. This novel reaction avoids the use of transition metal catalyst. Furthermore, the reaction are very mild and operational convenient.     

Synthesis of indoles through Rh(III)-catalyzed C–H cross-coupling with allyl carbonates

A practical Rh-catalyzed reaction was developed to achieve 2-alkyl-substituted indole synthesis. The reaction can tolerate a variety of synthetically important functional groups. The indole products can also be transformed into other important skeletons. Two bioactive compounds, that is indomethacin and pravadoline were prepared using the new method.     

Synthesis of CF3-substituted isoindolones via rhodium(iii)-catalyzed carbenoid C–H functionalization of aryl hydroxamates

An efficient method for the selective preparation of trifluoro-methyl-substituted isoindolones has been developed via Rh^III catalyzed C-H activation / [4 + 1]-annulation of aryl hydroxamates with functionalized acceptor/acceptor diazo compounds as cross-coupling partners.