A novel synthesis of 5-substituted isoxazoles from propargylic amines and N-hydroxyphthalimide

A mild and efficient method for the synthesis of 5-substituted isoxazoles through cyclization of propargylic amines with N-hydroxyphthalimide (NHPI) under metal-free conditions was developed.     

A visible-light-promoted cross-dehydrogenative-coupling reaction of N-arylglycine esters with imidazo[1,2-a]pyridines

A mild and convenient visible-light-promoted cross-dehydrogenative-coupling reaction between N-arylglycine esters and imidazo[1,2-a]pyridines for the construction of CC bond was developed. A range of N-arylglycine esters and imidazo[1,2-a]pyridines were able to undergo the CDC reaction readily to afford α-heteroaryl substituted α-amino acid derivatives in good to excellent yields. A tentative mechanism for the photoredox reaction was also proposed. Importantly, the use of copper(II) salt as the sole catalyst in this visible-light-promoted transformation makes this reaction sustainable and practical.     

Palladium-catalyzed arylation/cyclization/desulfonation cascades toward 4-aryl quinolin-2(1H)-ones with diaryliodonium salts

Palladium-catalyzed cascades of arylation/cyclization/desulfonation of ortho-aminocinnamate esters by using diaryliodonium salts afforded a wide range of 4-aryl quinolin-2(1H)-ones. As such, the desired 4-aryl quinolin-2(1H)-ones with potential biological activity has been synthesized in the yields of 34–96%.     

Highly stereoselective synthesis of (Z)-3-methoxy-1-methyleneisoindoles via DMAP catalyzed cyclization of methyl 2-alkynylbenzimidates

A DMAP (4-dimethylaminopyridine) catalyzed cyclization of methyl 2-alkynylbenzimidates has been developed, which affords 3-methoxy-1-methyleneisoindoles with excellent Z-stereoselectivity under mild and transition-metal-free conditions. The (Z)-3-methoxy-1-methyleneisoindole products can be converted to corresponding 3-amino-1-methyleneisoindoles, 3-methoxy-isoindoles, 3-methyleneisoindolinones and isoindolinones with high efficiency.     

Geometry,stability and aromaticity of β-diketiminate-coordinated alkaline-earth compounds

Alkaline-earth (Ae) metals have attracted a wealth of interdependent research from synthetic chemists. In Ae-catalyzed organometallic reactions, β-diketiminate is a typical ligand used to stabilize Ae catalysts by forming six-membered rings comprising Ae metals. Herein, studies focusing on the configuration of β-diketiminate-coordinated Ae compounds observed that the CC and CN bonds are homogeneous and unchanged. Furthermore, energetic studies observed that the formation of the Ae-incorporated six-membered rings results in enhanced stability of >20 kcal/mol. The nucleus-independent chemical shifts, anisotropy of the induced current density, and molecular orbital analyses demonstrated the non-aromaticity of the β-diketiminate-coordinated Ae compounds. The improved stability of these compounds can be explained by the delocalization of the π electrons derived from the β-diketiminate moiety.     

An expeditious entry to rare tetrahydroimidazo[1,5-c]pyrrolo[1,2-a]pyrimidin-7(8H)-ones: A single-step gateway synthesis of glochidine congeners

A single-step gateway synthesis of glochidine and its congeners that possess the rare uncommon tetrahydroimidazo[1,5-c]pyrrolo[1,2-a]pyrimidine core was developed employing histamine and readily available γ-ketoesters. Key features of the developed reaction involve tandem three C–N bonds formation and concomitant annulation of two rings in one pot to access this unique and complex tricyclic structure. Exploration of the unknown bioactivity of these compounds revealed that they elicit antiproliferative activity comparable to the anticancer drug imatinib against 6 cancer cell lines.     

Gold-catalyzed cyclization of enediynes and arenediynes to 6H-benzo[c]chromen-6-one and dibenzo[c,h]chromen-6-one derivatives

The efficient synthesis of 6H-benzo[c]chromen-6-one and dibenzo[c,h]chromen-6-one derivatives is described. Thus, treatment of arenediynes 1 and enediynes 5 with 5?mol % Ph₃PAuCl and 10?mol % of AgSbF₆ in refluxing toluene gave dibenzo[c,h]chromen-6-ones 4 and 6H-benzo[c]chromen-6-ones 6, in good yields, respectively.     

Nd(OTf)3-catalyzed intramolecular-intermolecular cascade cyclization reaction: An access to phenanthro[9,10-b]furan derivatives

An intramolecular-intermolecular cascade cyclization reaction via multi metal-carbene intermediates has been developed. This reaction uses catalytic amount of Nd(OTf)₃, which actives both alkyne and aldehyde moieties. This protocol provides a novel strategy for the synthesis of phenanthro[9,10-b]furans.     

Chemoselective aerobic oxidation of 2-amino-N-benzylanilines into N-(2-aminophenyl)imines via a nitroxide-free copper catalysis

Chemoselective oxidative synthesis of N-(2-aminophenyl)imines from 2-amino-N-benzylanilines was accomplished through combined use of O₂(air) and copper salt. This transformation was performed at room temperature, and the mild oxidation was efficient and chemoselective without using nitroxyl radicals and ligands.     

Synthesis of ferrocene-based phosphine ligands via Cu-catalyzed reductive coupling of ferrocenyl ketone-derived tosylhydrazones and H-phosphorus oxides

Ferrocene-based phosphine oxides with various substituents at phosphorous atoms were synthesized by Cu-catalyzed reductive coupling of ferrocenyl ketone-derived tosylhydrazones and H-phosphorus oxides. Followed by the reduction of ferrocene-based phosphine oxides, 1-substituted ferrocene-based phosphine ligand 7 and 1,1′-disubstituted ferrocene-based phosphine ligand 9 were obtained. Josiphos type ligand 8 were produced after ortho-lithiation of 7 and trapping with chlorodiphenyl phosphine or chlorodicyclohexylphosphine.     

Copper-catalyzed aryldifluoromethylenation of N-arylacrylamides to synthesis of the diheterocyclic compounds linked by gem-difluoromethylene moiety

An efficient method of copper-catalyzed aryldifluoromethylenation of N-arylacrylamides is described to step-economic synthesis of the various biologically important biheterocyclic compounds linked by gem-difluoromethylene moiety through addition of benzo-1,3-azolic (oxa- or thia-)difluoromethyl radicals generated in situ to terminal of C–C double bond of N-arylacrylamides then cyclization cascade. This protocol has demonstrated to have broad substrate scope and excellent functional-group tolerance under mild reaction conditions.     

Water-controlled nitro-oximation of alkenes under catalyst-free conditions

A convenient and precise nitration and oximation of alkenes with tert-butyl nitrite has been reported, yielding α-nitro ketoximes in satisfactory yields with broad substrate generality and excellent stereoselectivity under mild conditions. Experiments indicate that tert-butyl nitrite serves as both NO and NO₂ sources and water plays a key role in this difunctionalization reaction.     

Stereoselective preparation of methylenecyclobutane-fused angular tetracyclic spiroindolines via photosensitized intramolecular [2+2] cycloaddition with allene

Irradiation of 3-(hexa-4,5-dienyl)indole derivatives in the presence of 3′,4′-dimethoxyacetophenone by a high-pressure mercury lamp through Pyrex glass gave the corresponding [2+2] cycloaddition products stereoselectively in high yields. The major product was a methylenecyclobutane-fused angular tetracyclic spiroindoline derivative produced by the [2+2] cycloaddition through a parallel orientation. The minor product was a hexahydromethanocarbazole derivative through a crossed orientation. Electron-withdrawing substituents, such as acyl or alkoxycarbonyl, on the indole nitrogen were suitable for this reaction.     

Copper(I)-promoted trifluoromethylthiolation of arenediazonium salts with AgSCF3

An efficient method for trifluoromethylthiolation of arenediazonium salts has been developed in mild conditions with a stable and convenient AgSCF₃. It provides a straightforward and convenient way for the synthesis of trifluoromethylthiolated compound from diazonium salts in moderate to good yields.     

Palladium-catalyzed annulation of 2-(aryldiazenyl) aniline with dimethyl sulfoxide to access N-aryl-1H-benzo[d]imidazol-1-amine

A palladium-catalyzed annulation of 2-(aryldiazenyl) aniline and dimethyl sulfoxide was developed to access N-aryl-1H-benzo[d]imidazol-1-amine in moderate to good yields. Activated by 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), DMSO served as a “CH” fragment during this procedure. It represents a facile pathway leading to benzimidazoles.     

Unexpected intramolecular nucleophilic cyclization of ureidoacetamide: A novel route towards the synthesis of 2,4,5-trisubsituted oxazoles

A variety of N, 2-diaryl-2-ureidoacetamide prepared from the condensation of N-aryl-α-aminoamide with potassium cyanate (KOCN) undergo efficient Hendrickson’s reagent-mediated nucleophilic cyclization to afford 2,5-diamine-4-aryloxazoles. The two-step synthesis provides seven target products in yields of 61–78% under mild conditions. This reaction involves an unusual pathway in which the electrophilic amide carbonyl carbon is activated by Hendrickson’s reagent and attacked by a nucleophilic ureido oxygen in a 5-exo-trig O-cycloisomerization.     

Acid-catalyzed highly diastereoselective and effective synthesis of 1,3-disubstituted tetrahydropyrano[3,4-b]indoles

We successfully explored for the first time that trifluoroacetic acid (TFA) can effectively catalyze the oxa-Pictet-Spengler reaction of secondary tryptophols and acetals to synthesize 1,3-disubstituted 1,3,4,9-tetrahydropyrano[3,4-b]indoles in high yield (up to >99%) and diastereoselectivity (>20:1). The secondary tryptophols were synthesized from indole-3-acetic acid. The one-pot synthesis of tetrahydropyrano[3,4-b]indoles was successfully developed from secondary tryptophols and in situ prepared acetals from aldehydes and trimethylorthoformate and thus the cost-efficiency of the protocol was effectively enhanced. Finally, the catalytic asymmetric synthesis of the 1,3-disubstituted tetrahydropyrano[3,4-b]indole was also demonstrated after enantioselective achievement of highly enantiopure secondary tryptophols.     

Efficient synthesis of 3-benzoyl Benzo[b]thiophenes and raloxifene via Mercury(II)-Catalyzed cyclization of 2-alkynylphenyl alkyl sulfoxides

The unique selective estrogen receptor modulator, Raloxifene (1), and antitubulin agent 2 were synthesized through the key intermediate, 4-methoxybenzyl 2-bromo-4-methoxyphenyl sulfoxide (6), respectively. It was found that compared with the o-sulfanyl aryl bromides, the sulfinyl group at ortho position accelerated the Sonogashira coupling reaction of aryl bromides. Thus, compound 6 was coupled with 3,4,5-trimethoxyphenyl acetylene, followed by mercury-catalyzed cyclization reaction afford compound 2 in 79% overall yield. Raloxifene (1) was prepared from compound 6 in four steps and 33% overall yield via coupling reaction with 1-trimethylsily-2-(4-tert-butyldimethylsiloxy)phenylethyne, mercury-catalyzed cyclization reaction, alkylation and demethylation.     

Stimuli-responsive fluorescent supramolecular polymer network based on a monofunctionalized leaning tower[6]arene

A fluorescent supramolecular polymer network with an excellent triple-stimuli responsive property based on metal–ligand coordination and host–guest interactions has been constructed from a terpyridine-monofunctionalized leaning tower[6]arene, a tetraphenylethylene AIEgen, and a bridging coordination ion (Zn²⁺). Addition of competitive binding agents, trifluoroacetic acid, and/or pillar[5]arene can break the metal coordination and/or host-guest inclusion complexation, and thermal heating can weaken the non-covalent interactions in the supramolecular polymer gel, all leading to the gel-to-sol transition.     

Copper-catalyzed cross-coupling of chloramine salts and arylboronic acids in water: A green and practical route to N-arylsulfonamides

A green and practical method for the synthesis of N-arylsulfonamides from chloramine salts and arylboronic acids is herein developed. The reaction proceeds readily in the presence of 5?mol% of CuI and 2.5?equiv. K₂CO₃ in water at room temperature, generating a variety of N-arylsulfonamides in moderate to good yields with good functional group tolerance.