Efficient three-component reactions of α-thiocyanato ketones stereoselectively forming E-3-aroylidene-2-oxindole derivatives

A new three-component reaction of α-thiocyanato ketones under microwave irradiation for the stereoselective synthesis of 25 examples of E-3-aroylidene-2-oxindole derivatives has been described. The domino reaction simultaneously installs C–S and C–C bonds through continuous [3+2] cycloaddition/ring opening of in situ generated 1,3-oxathiolanes/S_N2-type reaction sequence.     

On the mechanism of Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones: density functional theory survey

In this article, we have theoretically investigated the possible reaction mechanisms for Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones. The ωb97X-D method and C-PCM solvent model are used to describe the reaction processes. After the formation of allenylpalladium through C–O bond cleavage from propargylic carbonates, both decarboxylation and ligand exchange processes are explored. Then, depending on different conditions, we considered three possible types of reaction mechanisms, carbene insertion triggered by N₂ release, C–C coupling reactions without N₂ release, and C–C coupling reactions via the out-sphere attack of diazo compound. Our results indicate that it is favorable to undergo the carbene insertion into allenylpalladium after ligand exchange with diazo compound, which is partially agreement with the experimental suggestions. Although the decarboxylation is more difficult than ligand exchange, the reaction rate could be limited by Pd-catalyzed N₂ dissociation from diazo compound. Additionally, it should be essential to select DFT-D method to describe this reaction.     

l-Proline-catalyzed three-component domino reactions for the synthesis of highly functionalized pyrazolo[3,4-b]pyridines

A series of novel N,3-dimethyl-5-nitro-1-aryl-1H-pyrazolo[3,4-b]pyridin-6-amines was obtained in good yields from the domino reactions of N-methyl-1-(methylthio)-2-nitroprop-1-en-1-amine, aromatic aldehydes, and 3-methyl-1-aryl-1H-pyrazol-5-amines in ethanol in the presence of green catalyst, l-proline. This transformation involves the formation of two C–C and one C–N bonds leading to the creation of a six-membered ring in a one-pot operation.     

Construction of fluorinated pyrazole derivatives via a one-pot tandem C–H insertion/electrophilic fluorination reaction

A series of 4-fluoro-pyrazole derivatives were synthesized in moderate to good yields via a one-pot tandem procedure involving an Rh₂(OAc)₄-catalyzed C–H insertion and an electrophilic fluorination with N-fluorobenzenesulfonimide (NFSI).     

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.     

Cu(OAc)2 promoted Chan–Evans–Lam C–N cross coupling reactions on the N- and N′-nitrogen atoms of sulfonimidamides with aryl boronic acids

We report a highly efficient and mild protocol for Chan–Evans–Lam C–N cross coupling of sulfonimidamides and aryl boronic acids using Cu(OAc)₂ as mediator, triethylamine (TEA) as base and acetonitrile as solvent. The reaction proceeds at room temperature and provides high to excellent yields for a variety of boronic acids, allowing N-arylation of both N-protected (N-amine nitrogen) and N-deprotected (N′-imine nitrogen) sulfonimidamides.     

[RuCl2(p-cymene)2]2 catalyzed cross dehydrogenative coupling (CDC) toward xanthone and fluorenone analogs through intramolecular C–H bond functionalization reaction

A synthetic approach toward xanthone and fluorenone derivatives through ruthenium catalyzed intra-molecular C–H bond functionalization using an external oxidant has been developed. In the presence of [RuCl₂(p-cymene)₂]₂, a variety of substituted ortho-aryloxy/aryl benzaldehydes underwent cross dehydrogenative coupling to afford the corresponding analogs in moderate to good 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.     

Naryl-substituted anthranilamides with intramolecular hydrogen bonds

Hydrogen bonding interaction as one type of non-covalent force has proven itself to be highly efficient for constructing structurally unique artificial secondary structures. Here, the structure of N_aryl-substituted anthranilamide in solution is demonstrated by various NMR technique, the intramolecular hydrogen bonds between amide attached to arylamine of the same ring is proposed, which is supported by its crystal structure in the solid phase. The substituent on the nitrogen atom of arylamine plays an important role in forming the presence of intramolecular hydrogen bonds. The chemical shift of the N_aryl-H downfield changes obviously, due to the formation of intramolecular hydrogen bonds and the deshielding effect of oxygen, and the neighboring C–H is activated and shows downfield protonic signal too. The presence of intramolecular hydrogen bonds probably provides the explanation for the transformation from N_aryl-substituted anthranilamide to imine, which could be converted into 2-aryl quinazolinone finally.     

Mercury(II) complex of inverted N-methylated porphyrin: HgPh(2-NCH3NCTPP)

The reaction of PhHgOAc with 2-NCH₃NCTPPH (2) gave a mercury(II) complex of (phenylato)(2-N-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″)-mercury(II), [HgPh(2-NCH₃NCTPP); 7]; the coordination sphere around Hg(1) in 7 was a four-coordinate derivative with a seesaw geometry and dipole–dipole (DD) interaction governed the longitudinal relaxation rate for Hg(1)–Ph–H_2,6 protons of 7 in CDCl₃ (0.01 M) at 599.95 MHz.     

Dimeric and polymeric silver(I) saccharinato complexes of two bis(pyridine) ligands: Synthesis,structural, spectroscopic,fluorescent and thermal properties

The reaction of silver(I) with 1,2-bis[1-(pyridin-2-yl)ethylidene]hydrazine (bpeh) and N,N-bis(pyridin-2-ylmethyl)amine (bpma) in the presence of Na(sac) (sac = saccharinate) yielded [Ag₂(sac)₂(bpeh)] (1) and [Ag(sac)(bpma)]_n (2) with conformational chirality. Both complexes have been characterized by elemental analysis, IR, thermal analysis and X-ray single crystal diffraction. Complex 1 displays a binuclear composition, in which each silver(I) ion is bound to one monodentate sac ligand and one of the bidentate pyridylimino groups of the bpeh ligand in a distorted trigonal coordination geometry. Complex 2 is a one-dimensional helical polymer, in which silver(I) centers are bridged by tridentate bpma ligands, and each silver(I) ion is coordinated in a distorted tetrahedral geometry by one monodentate sac ligand, a bidentate pyridylamine group of one bpma ligand, and a py group of another bpma ligand. Weak intermolecular C–H?O hydrogen bonds and C–H?π interactions lead to assembly of 1 and 2 into three-dimensional supramolecular frameworks. Spectral and thermal analysis data for 1 and 2 are in agreement with the crystal structures. In addition, both complexes in the solid state display intraligand π–π∗ fluorescence.     

An expedient approach to substituted triazolo[1,5-a][1,4]benzodiazepines via Cu-catalyzed tandem Ullmann C–N coupling/azide-alkyne cycloaddition

An approach to the synthesis of triazolo[1,5-a][1,4]benzodiazepines comprising copper catalyzed tandem Ullmann C–N coupling followed by azide-alkyne cycloaddition has been described. The reaction of o-azidobenzylbromide and N-propargylated aniline derivatives in the presence of CuI and base leads to the formation of triazolo[1,5-a][1,4]benzodiazepines. The reaction has been successfully generalized by synthesizing a number of triazolo[1,5-a][1,4]benzodiazepine derivatives in good to excellent yields.     

Regioselective ortho-acetoxylation/methoxylation of N-(2-benzoylphenyl)benzamides via substrate directed C-H activation

A highly regioselective ortho-acetoxylation of N-(2-benzoylphenyl)benzamides has been achieved using a catalytic amount of Pd(OAc)₂ (10 mol %) and a stoichiometric amount of PhI(OAc)₂ in a mixture of acetic anhydride and acetic acid via C-H activation to produce the corresponding 2-acetoxybenzamides in good yields. ortho-Methoxylation has been accomplished using methanol under similar conditions.     

Sequential one-pot method for oxy-Michael addition,Heck coupling,and degradation followed by condensation: facile synthesis of 2-benzoxepin-3(1H)-ones

A sequential one-pot intermolecular oxy-Michael addition, intermolecular Heck coupling, and intramolecular degradation (retro-oxy-Michael addition) followed by condensation method has been developed for the synthesis of interesting 2-benzoxepin-3(1H)-ones. Significantly, the 2-benzoxepin-3(1H)-ones form the core quantum of biologically vital natural products. The initial oxy-Michael addition and Heck coupling steps involve a straight forward construction of C–O and C–C bonds, whereas, the final condensation step follows a novel mechanistic path via intramolecular degradation, double bond isomerization, and intramolecular condensation. Notably, a remarkable solvent effect has been observed in-order to promote the final intramolecular condensation.     

Application of N,3-diaryl-3-oxo-propanethioamide in synthesis: an efficient and mild domino approach to highly substituted fused chromenones

A convenient and rapid synthesis of hitherto unknown 3-aroyl-4-aryl-2-phenylamino-4H-benzo[g]chromene-5,10-diones in high yield from β-aroyl-thioacetanilide, aromatic aldehyde, and 2-hydroxy-1,4-naphthoquinone via InCl₃ catalyzed one-pot three-component tandem Knoevenagel condensation–Michael addition–intramolecular cyclization–elimination reaction sequence is disclosed for the first time. This domino protocol has been used to obtain highly substituted pyrano[3,2-c]chromen-5(4H)-ones and 7,7-dimethyl-7,8-dihydro-4H-chromen-5(6H)-ones from N,3-diaryl-3-oxo-propanethioamide, aromatic aldehyde, and 4-hydroxycoumarine or dimedone under mild reaction conditions. A plausible reaction mechanism is proposed. The 4H-pyrano[3,2-c]chromen-5-one and 7,7-dimethyl-7,8-dihydro-4H-chromen-5(6H)-one derivatives possessing 3-(2-chlorobenzoyl)-2-phenylamino-substituents further cyclized under basic conditions to yield penta-cyclic 7,13-diaryl-5,14-dioxa-13-aza-benzo[a]naphthacen-6,8(7H,13H)-dione and tetra-cyclic 6,12-diaryl-3,3-dimethyl-3,4-dihydro-2H-chromeno[2,3-b]quinolin-1,11(6H,12H)-dione, respectively.     

Unexpected cleavage of the Cpy–Cpy bond in the reaction of 2,2′-bipyridine N,N′-diimines with acetylenes

An unusual cleavage of the C_py–C_py bond in the reaction of 2,2′-bipyridine N,N′-diimine and its C-methyl substituted derivatives with acetylenes is described. The effect of the solvent on the yield of 7,7′-bipyrazolo[1,5-a]pyridine-2,2′,3,3′-tetracarboxylates and the products of cleavage of the C_py–C_py bond has been studied. The mechanism of the cleavage reaction is discussed on the basis of DFT calculations.     

Reactivity of M(en)Cl2 (M = Pd/Pt,en = 1,2-diaminoethane) with N,N′-bis(salicylidene)-p-phenylenediamine: Binding with hexafluorobenzene

Schiff base N,N′-bis(salicylidene)-p-phenylenediamine (LH₂) complexed with Pt(en)Cl₂ and Pd(en)Cl₂ provided [Pt(en)L]₂ · 4PF₆ (1) and Pd(Salen) (2) (Salen = N,N′-bis(salicylidene)-ethylenediamine), respectively, which were characterized by their elemental analysis, spectroscopic data and X-ray data. A solid complex obtained by the reaction of hexafluorobenzene (hfb) with the representative complex 1 has been isolated and characterized as 3 (1 · hfb) using UV–Vis, NMR (¹H, ¹³C and ¹⁹F) data. A solid complex of hfb with a reported Zn-cyclophane 4 has also been prepared and characterized 5 (4 · hfb) for comparison with complex 3. The association of hfb with 1 and 4 has also been monitored using UV–Vis and luminescence data.     

Isolation and synthesis of N-acyladenine and adenosine alkaloids from a southern Australian marine sponge, Phoriospongia sp.

Chemical fractionation of the southern Australian marine sponge Phoriospongia sp. (CMB-03107) yielded phorioadenine A (1) as a nematocidal agent and the first reported example of a 6-N-acyladenine natural product. The structure of 1 was confirmed by spectroscopic analysis and the chemical synthesis of racemic (1a) and enantiomeric (1b) analogues. HPLC–ESIMS analysis of the crude sponge extract with comparisons to the synthetic 6-N-acyladenosine 2a provided evidence that the biosynthetically related adenosine, phorioadenosine A (2), was present as a trace co-metabolite. The rare starfish metabolite asterubine (3) was also isolated as a co-metabolite, and its structure confirmed by spectroscopic analysis and chemical synthesis. Biological investigations confirmed that natural products 1–3 and synthetic analogues 1a–e and 2a were not cytotoxic to multiple mammalian cancer cell lines, or Gram-positive or -negative bacteria. Nematocidal activity (inhibition of larval development of Haemonchus contortus) detected in the Phoriospongia sp. extract was attributed to 1 (LD₉₉ 31 μg/mL), with preliminary structure–activity relationship investigations confirming the importance of the N-acyl side chain.     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.