Iodine and Brønsted acid catalyzed C–C bond cleavage of 1,3-diketones for the acylation of amines

Abstract

A metal-free N-acylation method of anilines with 1,3-diketones has been developed, by using iodine and p-toluene sulfonic acid as the co-catalysts. The reaction can proceed in 1,4-dioxane at elevated temperature to produce the corresponding amides with 48–89% yields. Further, the gram-scale experiment was carried out under the standard conditions and the possible mechanism was proposed.     

Copper and zinc co-catalyzed synthesis of imidazoles via the activation of sp C–H and N–H bonds

An efficient and facile approach to synthesize imidazoles from amidines and arylketone via oxidative coupling of sp³ C–H bond and N–H bond is reported. This strategy exhibits high performance in terms of regioselectivity with moderate to high yields by using easily available materials, and provides an alternative method to synthesize multi-substituted imidazole skeletons.     

Cp*Co(III) catalyzed annulation of N-Cbz hydrazones for the redox-neutral synthesis of isoquinolines via C–H/N–N bond activation

Abstract

A new cascade oxidative cyclization reaction of N-Cbz hydrazones with internal alkynes has been explored for the preparation of isoquinoline derivatives using Cp*Co^III-catalyst through C–H and N–N bond functionalization. N-Cbz hydrazones are rarely explored as directing group for redox-neutral [4?+?2] cyclization reaction through the cyclometallation and this catalyst system does not require any external oxidizing agent, as well as, silver or antimony salt. The current efficient approach has been utilized for the synthesis of different isoquinoline derivatives with good regioselectivity and yields.     

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.     

Pd(II)-catalyzed intramolecular C–H activation/C–C cross coupling for the synthesis of carbazoles from diaryl acetamides

Pd(II)-catalyzed intramolecular C–H activation/C–C cross coupling within N,N-diphenyl-acetamides allows the efficient formation of differently substituted carbazoles. In this cross-dehydrogenative coupling, many different functional groups are tolerated and the starting material N,N-diphenyl-acetamides can be easily prepared in one step from commercially available acetanilides and iodobenzenes.     

Trialkyl borate assisted amination of fluorinated 1,3-diketones for synthesis of N,N′-1,2-phenylen-bis(β-aminoenones) and their Ni(II), Cu(II) and Pd(II) complexes

An effecient synthetic method for fluorinated tridentate β-aminoenones and tetradentate bis(β-aminoenones) via amination of fluorinated 1,3-diketones with o-phenylenediamine in the presence of trialkyl borates was developed. Ni(II), Cu(II) and Pd(II) complexes with tetradentate bis(β-aminoenones) were obtained. Their gaschromatographic behaviour and main fragmentation paths in the electron ionization mass spectra were described.     

Total synthesis of podophyllotoxin and select analog designs via C–H activation

An account of our previously disclosed total synthesis of the aryltetralin lignan natural product podophyllotoxin, a building block used in the synthesis of the FDA-approved anticancer drug etoposide, is disclosed. A C–H activation disconnection was viewed as being amenable to the preparation of E-ring modified analogs but proved challenging to execute. Various insights into palladium-catalyzed C–H arylation reactions on complex scaffolds are reported ultimately leading to the implementation of this strategy and the synthesis of compounds inaccessible by semisynthetic means.     

Solvent-free rhodium(III)-catalyzed synthesis of 2-aminoanilides via C−H amidation of N-nitrosoanilines under ball-milling conditions

A solvent-free rhodium(III)-catalyzed C?H amidation of N-nitrosoanilines with 1,4,2-dioxazol-5-ones has been successfully developed under ball-milling conditions. This protocol provides an efficient and green access to a variety of 2-aminoanilide derivatives with low catalyst loading, remarkable functional group compatibility and excellent yields. In addition, the products allow convenient access to pharmaceutically valuable benzimidazole derivatives through a one-pot two-step synthesis.     

Rh(III)-Catalyzed Oxidative Annulation of 2-Arylquinoxalines with Cyclic 2-Diazo-1,3-diketones by C−H Bond Activation

Rh(III)-catalyzed C−H bond annulation of 2-arylquinoxalines with cyclic 2-diazo-1,3-diketones has been accomplished for the first time to synthesize a novel series of 2,3-dihydrodibenzo[a,c]phenazin-4(1H)-one frameworks by means of carbene insertion followed by condensation. The reaction proceeds through the C−H bond activation and functionalization of 2-arylquinoxalines using Rh(III)/AgSbF₆ complex to produce highly substituted 2,3-dihydrodibenzo[a,c]phenazin-4(1H)-one and benzo[5,6][1,2,4]thiadiazino[2,3-f]phenanthridin-5(6H)-one-10,10-dioxide derivatives in good to excellent yields.     

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 indoles from 1-alkylidene-2-arylhydrazines and alkynes via C–H and N–N bond cleavages

1-Alkylidene-2-arylhydrazines undergo annulative coupling with internal alkynes in the presence of a rhodium(III) catalyst and a copper(II) salt. The reaction proceeds through cleavage of the C–H and N–N bonds of hydrazines to afford 1,2,3-trisubstituted indole derivatives.     

Transition-metal-free site-selective C–F bond activation for synthesis of 8-aminoquinolines

An efficient and general selective method for the synthesis of 8-aminoquinoline derivatives has been disclosed through transition metal direct C–N coupling from fluoroquinolines and arylamines. Significantly, good chemo- and regio-selectivity was observed for polyfluoroquinolines in which only C–F bond on 8-substituted position was broken. Thus, this methodology proves its value as an inexpensive and efficient synthetic way to access quinolin-8amine derivatives in moderate to good yields.     

Stereoselective tribromomethylation of N-(tert-butanesulfinyl)imines with bromoform: practical synthesis of α-tribromomethyl amines

The unprecedented nucleophilic tribromomethylation of N-(tert-butanesulfinyl)imines with bromoform has been shown to be a highly stereoselective and practical method for the synthesis of enantiomerically pure α-tribromomethyl amines. THF has proven to be the best solvent in this addition reaction. By changing the reaction solvent from THF to DMF, 2,2-dibromoaziridines can also be synthesized directly from bromoform and N-(tert-butanesulfinyl)imines under similar reaction conditions.     

Recent strategic advances for the activation of benzylic C–H bonds for the formation of C–C bonds

Alkylarenes, obtained from abundant hydrocarbon feedstock sources, are an attractive starting material for the formation of complex molecular architectures. Conventional activation strategies of the relatively inert sp³-hybridized benzylic C–H bonds usually require relatively harsh conditions and are difficult to apply to the synthesis of fine chemicals. The present review describes recent strategic advances for the activation of benzylic C–H bonds for the catalytic formation of C–C bonds. In particular, two activation methods, i.e., strategies that generate benzylic radicals or benzyl anions, are discussed.     

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.     

Ni-mediated C–N activation of amides and derived catalytic transformations

Amide, as a ubiquitous functional group, is essential in various aspects of chemistry and biology. Although the history of studying amide is rich and fruitful, the synthetic application of amide is very limited due to the inertness of amide C–N bond. Recently,significant advances have been achieved towards the nickel-mediated C–N activation of amides. This approach allows a facile generation of acyl-nickel intermediates, and a number of unique transformations have been designed and realized based on the amide C–N bond activation. Focused on the catalytic transformation, this review summarizes and categorizes the recent advances on the synthetic applications of Ni-mediated C–N bond activation of amides.     

Selective C-N bond oxidation: demethylation of N-methyl group in N-arylmethyl-N-methyl-α-amino esters utilizing N-iodosuccinimide (NIS)

Demethylation of N-methyl group in N-methyl-N-arylmethyl-α-amino esters was accomplished by the oxidation of the amino group using the N-iodosuccinimide (NIS)/acetonitrile system followed by treatment with O-methylhydroxylamine hydrochloride. This combination of reagents could provide a complementary method to catalytic hydrogenolysis, which certainly cleaves N-arylmethyl groups, in organic synthesis.     

Catalytic borylation of o-xylene and heteroarenes via C–H activation

Iridium and rhodium complexes catalyze the borylation of xylene and different heteroarenes using pinacolborane via C–H activation. Various five-membered heterocycles such as thiophene, pyrrole, thionaphthene, and indole derivatives yield the borylated products in moderate to good yields. In general, the reactions proceed with high selectivity to give borylation ortho to the heteroatom.     

FTIR study of the sol–gel synthesis of cementitious gels: C–S–H and N–A–S–H

The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the blended material.

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.