Furopyridines. XI. 13C NMR Spectra of 2- or 3-Substituted Furo[2,3-b]-, Furo[3,2-b]-, Furo[2,3-c]- and Furo[3,2-c]pyridine

The ¹³C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.     

A new approach for the synthesis of some pyrazolo[5,1‐c]triazines and pyrazolo[1,5‐a]pyrimidines containing naphtofuran moiety

Naphtho[2,1‐b]furan‐2‐yl)(8‐phenylpyrazolo[5,1‐c][1,2,4]triazin‐3‐yl)methanone, ([1,2,4]triazolo[3,4‐c][1,2,4]triazin‐6‐yl)(naphtho[2,1‐b]furan‐2‐yl)methanone, benzo[4,5]imidazo[2,1‐c][1,2,4]triazin‐3‐yl‐naphtho[2,1‐b]furan‐2‐yl‐methanone, 5‐(naphtho[2,1‐b]furan‐2‐yl)pyrazolo[1,5‐a]pyrimidine, 7‐(naphtho[2,1‐b]furan‐2‐yl)‐[1,2,4]triazolo[4,3‐a]pyrimidine, 2‐naphtho[2,1‐b]furan‐2‐yl‐benzo[4,5]imidazo[1,2‐a]pyrimidine, pyridine, and pyrazole derivatives are synthesized from sodium salt of 5‐hydroxy‐1‐naphtho[2,1‐b]furan‐2‐ylpropenone and various reagents. The newly synthesized compounds were elucidated by elemental analysis, spectral data, chemical transformation, and alternative synthetic route whenever possible. J. Heterocyclic Chem., (2012).     

Synthesis and photochemical reactivity towards the Paternó–Büchi reaction of benzo[b]furan derivatives: their use in the preparation of 3-benzofurylmethanol derivatives

4-Amino-2,7-dimethylbenzo[b]furan and 4-chlorobenzo[b]furan have been synthesized. The irradiation of 4-amino-2,7-dimethylbenzo[b]furan in the presence of benzaldehyde gave the corresponding endo adduct. The adduct can be hydrolysed to the corresponding 3-benzofurylmethanol derivative. The irradiation of the same compound in the presence of benzophenone gave the corresponding adduct. 4-Chlorobenzo[b]furan did not react with benzaldehyde while, in the presence of benzophenone, gave the corresponding adduct. The hydrolysis of this adduct gave the corresponding 3-benzofurylmethanol derivative.     

Friedel-Crafts alkylation of benzo[b]furan with activated cyclopropanes catalyzed by a calcium(II) complex

The synthesis of γ-benzo[b]furanyl malonates was achieved through the addition of benzo[b]furan to activated cyclopropanes. These Friedel-Crafts reactions were catalyzed by calcium bis(trifluoromethanesulfonimide), Ca(NTf₂)₂ with tetrabutylammonium hexafluorophosphine as a co-catalyst. The additions proceeded with complete regioselectivity and in good to excellent yield. Optimization of the reaction conditions and investigation into the scope of the methodology with regards to substitution on the cyclopropane are reported.     

Tellurium in organic synthesis: X. Synthesis of 3-halogenobenzo [b] tellurophene derivatives

Several substituted 3-halogenobenzo[b] tellurophenes have been synthesized by treating phenylacetylenes with TeO₂ in acetic acid in the presence of a lithium halide. A mechanism is postulated involving an electrophilic attack by a solubilized tellurium species on the acetylenic bond with introduction of a halogen atom followed by cyclization to the benzo[b]tellurophene system. The benzo[b]tellurophenes can be easily chlorinated with Cl₂ gas to yield benzo[b]tellurophene 1,1-dichloride derivatives, but attempted lithiation is the 3-position was unsuccessful and resulted in a ring rupture. When refluxed in trifluoroacetic acid 3-chlorobenzo[b]tellurophene was converted into 3-oxo-2,3-dihydrobenzo[b]tellurophene.     

New octahedral bis(diphenylphosphino)methanide derivatives and heterometallic species from mixed ligand isocyanide-dppm iron(II) complexes

The cationic [FeL(dppm)(CNPh)₃]ⁿ⁺ (1a: L = I, n = 1; 1b: L = CNPh, n = 2) are readily deprotonated by KOH to give [FeL(dppm-H)(CNPh)₃]ⁿ⁻¹ (2a and 2b). 2a reacts with [thtAuPPh₃]PF₆ to give mer-[FeI((PPh₂)₂C(H)(AuPPh₃))-(CNPh)₃]PF₆ (3). The new heterotrimetallic species [FeL((PPh₂)₂C(AuPPh₃)₂)-(CNPh)₃]ⁿ⁺ (4a and 4b) have been obtained from 1a and 1b by treatment with ClAuPPh₃ in the presence of KOH.     

New Synthetic Approach to Naphtho[1,2‐b]furan and 4′‐Oxo‐Substituted Spiro[cyclopropane‐1,1′(4′H)‐naphthalene] Derivatives

A one‐step synthesis of ethyl 2,3‐dihydronaphtho[1,2‐b]furan‐2‐carboxylate and/or ethyl 4′‐oxospiro[cyclopropane‐1,1′(4′H)‐naphthalene]‐2′‐carboxylate derivatives 2 and 3 , respectively, from substituted naphthalen‐1‐ols and ethyl 2,3‐dibromopropanoate is described (Scheme 1). Compounds 2 were easily aromatized (Scheme 2). In the same way, 3,4‐dibromobutan‐2‐one afforded the corresponding 1‐(2,3‐dihydronaphtho[1,2‐b]furan‐2‐yl)ethanone and/or spiro derivatives 8 and 9 , respectively (Scheme 6). A mechanism for the formation of the dihydronaphtho[1,2‐b]furan ring and of the spiro compounds 3 is proposed (Schemes 3 and 4). The structures of spiro compounds 3a and 3f were established by X‐ray structural analysis. The reactivity of compound 3a was also briefly examined (Scheme 9).     

1H NMR spectra of the 2-trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene

The ¹H NMR spectra of the 2-trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene were recorded at 200MHz in two solvents, chloroform and acetone. A long-range coupling constant, 5J(HF), between the fluorine nuclei of the trifluoroacetyl group and H-3, of a value higher than 1 Hz, was measured. From the comparison of the ¹H chemical shifts of, and the solvent effects on, the trifluoroacetyl compounds and those of the corresponding 2-acetyl derivatives, and on the basis of an empirical interpretation of the ⁵J(HF) coupling constant, a predominant Z conformation was tentatively assigned to these derivatives.     

Preparation of novel pyridine-fused tris-heterocycles; pyrido[4,3-e]pyrrolo-/pyrido[4,3-e]furano[2,3-c]pyridazines and pyrido[3,4-b]pyrrolo[3,2-d]pyrrole

Three novel pyrido-fused tris-heterocycles have been prepared based on a Suzuki coupling and subsequent cyclisation approach. Pyrido[4,3-e]pyrrolo[2,3-c]pyridazine (3b, 77%) and pyrido[4,3-e]furano[2,3-c]pyridazine (5b, 76%) were obtained by intramolecular diazocoupling. Successful diazocoupling of furan (5b) is thus reported for the first time by NOBF₄ generation of the diazonium intermediate. N-TIPS-pyrido[3,4-b]pyrrolo[3,2-d]pyrrole (TIPS-4b) was synthesised by thermal cyclisation of pyridyl nitrene in considerably higher yield (71%) than previously experienced from similar cyclisations, due to TIPS-activation.     

Constrained geometry complexes of titanium (IV) and zirconium (IV) involving cyclopentadienyl fused to thiophene ring

Constrained geometry complexes (CGCs) of titanium (IV) and zirconium (IV) containing isomeric cyclopentadienyls fused to thiophene fragment, i.e., 4,5-dimethylcyclopenta[b]thienyl and 5,6-dimethylcyclopenta[b]thienyl, have been prepared and unambiguously characterized. The molecular structure of the titanium complex [η⁵-(5,6-dimethylcyclopenta[b]thienyl)SiMe₂(N^tBu)-η¹]TiCl₂ was established by X-ray crystal structure analysis. Preliminary studies showed that the studied CGCs/MAO are active olefin polymerization catalysts.     

Synthesis of Novel N-Acylhydrazones and Their C-N/N-N Bond Conformational Characterization by NMR Spectroscopy

In this article, a synthesis of N’-(benzylidene)-2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetohydrazides and their structural interpretation by NMR experiments is described in an attempt to explain the duplication of some peaks in their ¹H- and ¹³C-NMR spectra. Twenty new 6-methyl-1H-pyrazolo[3,4-b]quinoline substituted N-acylhydrazones 6(a–t) were synthesized from 2-chloro-6-methylquinoline-3-carbaldehyde (1) in four steps. 2-Chloro-6-methylquinoline-3-carbaldehyde (1) afforded 6-methyl-1H-pyrazolo[3,4-b]quinoline (2), which upon N-alkylation yielded 2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetate (3). The hydrazinolysis of 3 followed by the condensation of resulting 2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetohydrazide (4) with aromatic aldehydes gave N-acylhydrazones 6(a–t). Structures of the synthesized compounds were established by readily available techniques such as FT-IR, NMR and mass spectral studies. The stereochemical behavior of 6(a–t) was studied in dimethyl sulfoxide-d₆ solvent by means of ¹H NMR and ¹³C NMR techniques at room temperature. NMR spectra revealed the presence of N’-(benzylidene)-2-(6-methyl-1H-pyrazolo[3,4-b]quinolin-1-yl)acetohydrazides as a mixture of two conformers, i.e., E_(C=N)(N-N) synperiplanar and E_(C=N)(N-N) antiperiplanar at room temperature in DMSO-d₆. The ratio of both conformers was also calculated and E_{(C=N) (N-N)} syn-periplanar conformer was established to be in higher percentage in equilibrium with the E_{(C=N) (N-N)} anti-periplanar form.     

Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

N-mesityl-N′-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N′-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl₃ · xH₂O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ²-2)₂Ru(μ-Cl)₂Ru(κ²-2)₂]²⁺ [3a]²⁺. The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-μ-bromo bridged derivative [(κ²-2)₂Ru(μ-Br)₂Ru(κ²-2)₂]²⁺ [3b]²⁺ was obtained from RuCl₃ · xH₂O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]²⁺ reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]⁺. Reaction of [3a]²⁺ with the sodium salt of l-proline resulted in a diastereomeric mixture of complexes [5]⁺. The free N-heterocyclic carbene 2 reacts with [FeCl₂(PPh₃)₂] to give after anion exchange with NaBPh₄ cis/cis/trans coordinated [Fe(κ²-2)₂(MeCN)₂](BPh₄)₂ [6](BPh₄)₂. The molecular structures of [3b](PF₆)₂, [4]PF₆ and [6](BPh₄)₂ · H₂O are reported.     

Theoretical study of H2 elimination from [B n H n + 1]− monoanions (n = 6–9, 11)

Transition states of elementary reactions of H₂ molecule elimination from [B _n H _{n + 1}]^? anions (n = 6–9, 11) in which nucleophilic/electrophilic vacancies form at boron atoms have been localized by the density functional theory method (in the B3LYP/6-311++G** approximation). For a series of [B _n H _{n + 1}]^? anions (n = 6–12), the activation barriers to H2 elimination have been compared to consider the possibility of substitution for exopolyhedral hydrogen atoms by the mechanism with the first rate-limiting stage of formation of [B _n H _{n ? 1}]^? (n = 6–12) intermediates with a vacant “bare” vertex of the boron cluster. For the [B _n H _n ]^2?, [B _n H _{n + 1}]^?, and [B _n H _{n ? 1}]^? anions (n = 6–12), the electronic chemical potential μ and Pearson hardness η have been evaluated since these characteristics make it possible to assess the propensity of different reagents to react with each other in terms of the empirical HSAB principle (soft with soft and hard with hard). The application of this principle is exemplified by the interaction of the [B₁₀H₉]^? and [B₁₂H₁₁]^? anions with acetonitrile CH₃CN, furan C₄H₄O, and 18-crown-6.     

Tautomeric crown-containing chemosensors for alkali-earth metal cations

Crown-containing arylimines of 5-hydroxy- and 5-hydroxy-6-nitro-2,3-diphenylbenzo[b]furan-4-carbaldehydes were synthesized and their structure, spectral, luminescent, and complexing properties were studied by means of ¹H and ¹³C NMR, IR, UV, and mass-spectrometry. In solution, these compounds exist as equilibrium mixtures of benzenoid and quinoid tautomers. The relative concentration of the quinoid form increases in the order of solvents: toluene, acetonitrile, 2-propanol, chloroform. The presence in the benzo[b]furan moiety of a strong withdrawing 6-NO₂ group favors stabilization of the quinoid tautomer. This finding is in accord with the results of the DFT B3LYP/6-311++g(d,p) calculations. Complexation of 5-hydroxy-6-nitro-2,3-diphenyl-1-benzofuran-4-carbaldehyde crown-containing imines with alkali and alkali-earth metal ions shifts the tautomeric equilibrium to the quinoid forms and is accompanied by blue shifts of the emission spectra. The Schiff bases obtained represent a new type of fluorescent tautomeric chemosensor for Mg²⁺, Ca²⁺ (benzo-15-crown-5 derivative), and Ba²⁺ (benzo-18-crown-6 derivative) displaying diagnostic changes in both absorption and emission spectra.     

Synthesis of 4-methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridine

4-Methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridine ( 3 ) was synthetized from 2-acetylfuro[3,2-f]benzo[b]furan ( 4 ) or from 2-acetyl-5,6-dihydrofuro[3,2-f]benzo[b]furan ( 10 ). The key step involves a rearrangement-cyclization of azides 6 and 12 to form 4-methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridin-1(2H) one ( 7 ) and 8,9-dihydro-4-methylfuro[3′,2′:5,6]benzofuro[3,2c]pyridin-1(2H)-one ( 13 ). Introduction of an aminoalkyl chain on carbon 1 was effected by substitution of 1-chloro-4-methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridine ( 8 ).     

Bis(trifluoromethyltellurato(0))metallates(I) of copper, silver and gold, [M(TeCF3)2] (M = Cu, Ag, Au)

Ligand exchange reactions of [NMe₄]TeCF₃ and CuBr, Ag[BF₄] and AuCl have been studied in molar ratios of 2:1. While evidence is found for [Cu(TeCF₃)₂]⁻ moieties by ¹⁹F-NMR spectroscopic and mass spectrometric means, [NMe₄][Ag(TeCF₃)₂] and [NMe₄][Au(TeCF₃)₂] were isolated. After cation exchange, the latter compounds were fully characterised as the [PNP] salts ([PNP] = bis(triphenylphosphoranylidene)ammonium). The single crystal structure of [PNP][Au(TeCF₃)₂] has been elucidated by XRD measurements (P2₁/a; a = 1765.6(1), b = 1126.0(1), c = 2055.2(1) pm; β = 111.98(1)°; Z = 4).     

13C NMR spectra of benzo[b]thiophene and 1-(X-benzo[b]thienyl)ethyl acetate derivatives

Carbon-13 chemical shift assignments are reported for benzo[b]thiophene and 1-(X-benzo[b]thienyl)ethyl acetate derivatives, where X=? CH(OAc)CH₃ substituted at positions 2-7. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift was observed at C-3, arising from the peri interaction of H-3 and the 4-ethyl acetate substituent. Carbon-13 relaxation times (T₁) and nuclear Overhauser enhancements (η) have been measured for benzo[b]thiophene and its derivatives, and the contributions of dipolar, T^DD₁, and spin rotation, T^SR₁, relaxation have been determined. Intramolecular dipole–dipole interactions are found to provide by far the most important spin-lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Nonprotonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T₁, and can form the basis for spectral assignments, as in 1-phenylethyl acetate. Long-range ¹³C? ¹H coupling constants were observed both between ring carbons and between ring carbons with ring side-chain hydrogens. These results have been used for the structure determination of the title compounds.     

The reaction between [Pt(cod)Cl(PMe2Ph)]BF4 and aryltrimethyltin compounds

The complex [Pt(cod)Cl(PMe₂Ph)]BF₄ reacts in dichloromethane with SnArMe₃ compounds having Ar = 2-thienyl, 2-benzol [b]thienyl, or 2-benzo[b]furyl to give air-stable cationic aryl complexes [Pt(cod)Ar(PMe₂Ph)]BF₄. No reaction takes place when Ar  Ph. The cod ligand in the new complexes can be readily replaced by ligands such as PMe₂Ph, dppe, or 4-dimethylaminopyridine. The¹H and³¹P-{¹H} NMR parameters of the various complexes are reported.     

Selenium heterocycles. XXXIII. Synthesis of thieno[3,4-b]furan,seleno[3,4-b]furan,thieno[3,4-b]indole and seleno[3,4-b]indole. four novel heterocycles

Starting from the readily available 2-methyl-3-benzoylfuran, 1-phenylthieno[3,4-b]furan and 1-phenyl-seleno[3,4-b]furan were prepared. Also, starting from phenyl 3-methylindol-2-yl ketone and aryl 2-methyl-indole-3-yl ketones a series of substituted thieno[3,4-b]indoles and substituted seleno[3,4-b]indoles were prepared.     

A novel efficient protocol for preparation of 3-formyl-2-arylbenzo[b]furan derivatives

An efficient method for preparation of 3-formyl-2-arylbenzo[b]furan derivatives 4 from 3-chloro-2-(2-methoxyaryl)-1-arylprop-2-en-1-one 2 was developed, and the desired product was obtained in good to excellent yields. By converting 2-(2-methoxyphenyl)-3-oxo-3-phenylpropanal 1 to 2, the regioselectivity problem occurring in the reaction when using 1 as the starting material was successfully avoided. Furthermore, a one-pot procedure for the successive demethylation, cyclization, and hydrolysis was evolved, although the intermediate 3-(dibromomethyl)-2-phenylbenzo[b]furan 3a could be isolated. A plausible mechanism was proposed based on some in situ investigations.