Highly selective acetoxylation of sulfonamides via using phenyliodine(III) diacetate

A highly efficient acetoxylation reaction of N-aryl-arylsulfonamides has been developed, presumably proceeding via the selective functionalization of N-aryl C–H bonds. A stoichiometric amount of PhI(OAc)₂ was generally employed as the oxidation reagent, and various para-acetoxylated sulfonamide derivatives had been generated in excellent yields. This chemistry endowed an economic synthesis of valuable acetoxylated sulfonamides through direct C–O bond formation processes.     

Density-functional study for the NOx (x = 1, 2) dissociation mechanism on the Cu(1 1 1) surface

Spin-polarized density functional theory calculation is employed to study the adsorption and dissociation of NO₂ molecule on Cu(1 1 1) surface. It is shown that the most favorable adsorption structure is the NO₂ (T,T-O-,O′-nitrito) configuration which has an adsorption energy of −1.49 eV. The barriers for step-wise NO₂ dissociation reaction, NO_2(g) → N_(a) + 2O_(a), are 1.05 (for O–N–O bond activation), and 2.08 eV (for N–O bond activation), respectively, and the entire process is 0.6 eV exothermic. The energetics of single N–O dissociation with and without the presence of N atom or O atom on the surface are also calculated. The results indicate that in the presence of O atom on Cu(1 1 1) surface would raise the N–O dissociation barrier, whereas in the presence of N atom decrease it. The interaction nature between adsorbates and substrate is analyzed by the local density of states (LDOS) calculation.     

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.     

Synthesis and structural characterization of [Bse]Ni(PPh3)(NO), a nickel complex with a bent nitrosyl ligand

The nickel nitrosyl compound [Bse^Me]Ni(PPh₃)(NO) has been synthesized by the reaction of Ni(PPh₃)₂(NO)Br with potassium bis(2-seleno-1-methylimidazolyl)hydroborate, [Bse^Me]K. X-ray diffraction studies demonstrate that (i) the B–H group of the [Bse^Me] ligand interacts with the nickel center and (ii) the nitrosyl ligand is bent, with Ni–N–O bond angles of 149.1(3)° and 153.1(3)° for the two crystallographically independent molecules. The bent nature of the nitrosyl ligand in [Bse^Me]Ni(PPh₃)(NO) is in marked contrast to the linearity observed for the tris(2-seleno-1-mesitylimidazolyl)hydroborato counterpart [Tse^Mes]NiNO (180.0°). Density functional theory geometry optimization calculations demonstrate that the Ni?H–B interaction is not responsible for causing the nitrosyl ligand to bend, but rather the difference between [Tse^Mes]NiNO and [Bse^Me]Ni(PPh₃)(NO) is due to the [Tse^Mes] ligand allowing the former molecule to adopt a structure with C₃ symmetry. In contrast, the steric and electronic asymmetry of [Se₂P] donor array of the [Bse^Me] and PPh₃ ligand combination prevents [Bse^Me]Ni(PPh₃)(NO) from having C₃ symmetry and the nitrosyl ligand bends to stabilize the occupied M–N σ^∗ antibonding orbital.     

One-pot three-component reaction for the synthesis of biologically important spiro[benzo[f]quinoline-3,3′-indoline] derivatives

A previously unknown class of highly substituted benzoquinoline–spirooxindole are easily prepared by a novel application of a mild and efficient catalyst SbCl₃ for carbon–carbon and carbon–nitrogen bond formation reaction involving isatin, alkyne (dialkyl but-2-ynedioate) with aromatic amine (2-naphthylamine) in a one-pot three-component reaction. This protocol of one-pot synthesis afforded a library of dialkyl 2′-oxo-4H-spiro[benzo[f]quinoline-3,3′-indoline]-1,2-dicarboxylate derivatives, a potential bioactive compound in very good to excellent yields.     

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.     

β-Tetra-brominated meso-tetraphenylporphyrin: A conformational study and application to the Mn-porphyrin catalyzed epoxidation of olefins with tetrabutylammonium oxone

X-ray crystallographic studies have shown that the free base β-tetra-brominated meso-tetraphenylporphyrin (H₂TPPBr₄) has a slightly ruffled structure with the dihedral angles of 70.1–79.2° between the phenyl groups and the porphyrin mean plane. The N(pyrrole)–N(pyrrolenine) distance is very similar to that of the standard planar porphyrins. The decreased N–H bond length of H₂TPPBr₄ with respect to that of meso-tetraphenylporphyrin (H₂TPP) seems to be due to the weaker intramolecular hydrogen bond of the former relative to the latter caused by the electron-withdrawing effects of the β-bromine substituents. The large red shifts of the Soret and Q(0,0) bands of H₂TPPBr₄ in comparison with those of H₂TPP, in spite of the nearly planar porphyrin core of the compound, also may be explained on the basis of the electron-withdrawing effects of the bromine atoms. Oxidation of styrene, the para-substituted derivatives and cyclooctene with tetrabutylammonium oxone in the presence of catalytic amounts of β-tetra-brominated meso-tetraphenylporphyrinatomanganese(III) acetate immediately gives the epoxide as the sole product. Terminal double bonds and unconjugated ones are less reactive than the conjugated double bonds and show lower selectivities. Catalytic activity of the electron-deficient Mn(H₂TPPBr₄)OAc dramatically depends on the Co-catalytic activity of the nitrogen donors as the axial base. The best axial bases are the nitrogenous donors with mixed σ- and π-donor ability to the metal centre.     

Neighbouring group participation in the reaction of 7-oxo-ent-kaur-16-ene derivatives with diacetoxyiodobenzene. Synthesis of gibberellin analogues

The reaction of different 7-oxo-ent-kaur-16-ene derivatives with diacetoxyiodobenzene has been evaluated for the preparation of gibberellin analogues. Thus, the reaction of 7-oxo-ent-kaur-16-en-18-oic acid methyl ester (3) with this reagent afforded 4-epi-GA₁₂ dimethyl ester (6). This reaction constitutes a good procedure for the preparation of this type of compounds. In some cases, alternative reactions that led to the introduction in the substrate of a conjugated 5,6-double bond or to the formation of a ketal at the 6-position were also produced. The formation of these compounds, or of gibberellin analogues, depends on the neighbouring group participation of the different C-18 and C-19 substituents at C-4.     

Tandem versus single C-C bond forming reaction under palladium-copper catalysis: regioselective synthesis of α-pyrones fused with thiophene

We herein report a highly convenient protocol for rapid construction of α-pyrone fused with thiophene. This includes one-pot and regioselective synthesis of 4,5-disubstituted and 5-substituted thieno[2,3-c]pyran-7-ones, 6,7-disubstituted and 6-substituted thieno[3,2-c]pyran-4-ones. The synthesis of thieno[2,3-c]pyran-7-ones involves palladium mediated cross coupling of 3-iodothiophene-2-carboxylic acid with terminal alkynes in a simple synthetic operation. The coupling-cyclization reaction was initially studied in the presence of Pd(PPh₃)₂Cl₂ and CuI in a variety of solvents. 5-Substituted 4-alkynylthieno[2,3-c]pyran-7-ones were isolated in good yields when the reaction was performed in DMF. Similarly, 6-substituted 7-alkynylthieno[3,2-c]pyran-4-ones were synthesized via palladium-catalyzed cross coupling of 2-bromothiophene-3-carboxylic acid with terminal alkynes. A tandem C-C bond forming reaction in the presence of palladium catalyst rationalizes the formation of coupled product in this apparently three-component reaction. The cyclization step of this coupling-cyclization-coupling process occurs in a regioselective fashion to furnish products containing six-membered ring only. This sequential C-C bond forming reaction however, can be restricted to the formation of single C-C bond by using 10% Pd/C-Et₃N-CuI-PPh₃ as catalyst system in the cross coupling reaction. 5-Substituted thieno[2,3-c]pyran-7-ones were obtained in good yields when the coupling reaction was performed under this condition. Some of the compounds synthesized were tested in vitro for their anticancer activities.     

C-N bond formation followed by N-Cl bond breaking. One more and unexpected case of the formation of a hydroxamic group via heterolytic bond cleavage

An unexpected and previously unknown reaction sequence in the interactions of the acyl halides with nitrosobenzenes, which involves carbon-nitrogen bond formation followed by heterolytic nitrogen-chlorine bond cleavage giving the corresponding unsubstituted N-phenylalkylhydroxamic acids (or N-phenylarylhydroxamic acids) and chlorine as the products has been observed. The kinetic and other evidence obtained suggest that the carbon-nitrogen bond formation is the consequence of a nucleophilic interaction of an N-phenylchlorohydroxylamine intermediate, formed in the first reaction step, with the acyl halide in the second step of the complex sequence, which leads to an N-acyl-N-chlorophenylhydroxylamine cation intermediate. The key reaction step involves the interaction of an N-acyl-N-chlorophenylhydroxylamine cation intermediate with chloride ion, which leads to the N-Cl heterolytic bond cleavage and the final formation of the hydroxamic group and a molecule of chlorine.     

Synthesis and characterization of coordination polymers of a carboxylato cyclophane with metal [Zn(II) and Cd(II)]-2,2′-bipyridines

N,N′,N′′,N′′′-Tetrakis(3-carboxy-propionyl)-1,6,20,25-tetraaza-[6.1.6.1] paracyclophane, H₄cp has been complexed with metal (Zn(II) and Cd(II)) 2,2′-bipyridyls. The resulting complexes of the composition [{Zn(2,2′-bpy)}₂(cp)]_n·4H₂O 1 and [{Cd(2,2′-bpy)}₂(cp)]_n·5H₂O 2 (2,2′-bpy = 2,2′-bipyridine) have been characterized using spectroscopic (IR, solid state UV–Vis), elemental analysis and single-crystal X-ray diffraction measurements. In these complexes the cyclophane coordinates in different modes, and in complex 2, Cd(II) is hepta-coordinated. However, under harsh reaction conditions (using excess nitric acid and a longer reaction time) debranching of the cyclophane is observed in the reaction of Zn(2,2′-bpy)(NO₃)₂ with H₄cp, and a complex of the composition [Zn(2,2′-bpy)(Suc)]_n3 (suc = succinate) is isolated. Using non-covalent interactions, complexes 1 and 2 provide 3D supramolecular structures, whereas an infinite 1D chain structure is observed for complex 3. The thermal and photoluminescence properties of the complexes have also been studied.     

Acid/base-regulated reversible electron transfer disproportionation of N–N linked bicarbazole and biacridine derivatives

Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N–N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N–N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt₃, which recovers TBA through back electron transfer and N–N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N–N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials.     

Synthesis of substituted tetrahydron-1H-carbazol-1-one and analogs via PhI(OCOCF3)2-mediated oxidative C–C bond formation

A variety of tetrahydro-1H-carbazol-1-ones and analogs were conveniently synthesized from the reaction of the corresponding 2-(phenylamino)cyclohex-2-enone with hypervalent iodine reagent PhI(OCOCF₃)₂ (PIFA), through a direct intramolecular oxidative C(sp²)–C(sp²) bond formation. This approach realized the construction of the biologically important tetrahydro-1H-carbazol-1-one and tetrahydrocyclohepta[b]indol-6(5H)-one skeletons. The mechanism of the process was proposed and briefly discussed.     

Formation of benzo[c]thiophen-1-aminium iodide by the reaction of o-alkynylbenzothioamide with iodine

Reaction of o-alkynylbenzothioamide with molecular iodine was investigated. Unique benzo[c]thiophen-1-aminium iodide was obtained when the tertiary thioamide was used as a reactant. The reaction proceeded efficiently in less polar solvent, whereas the corresponding product was also obtained in a polar solvent. Single crystal X-ray analysis revealed that the benzo[c]thiophen-1-aminium structure possesses a resonance structure in N–C–S bond. Its stabilization shows a clear difference in the result from the reaction of amide analogue with iodine to give no stable compound.