Ring Contraction Products Research Articles

Preparation and characterization of Pt/HMFI–SBA-15 hybrid catalyst for tetralin transformation

A Pt catalyst supported on a hybrid material, HMFI–SBA-15, was prepared. Both, support and catalyst (Pt/HMFI–SBA-15) were characterized by nitrogen physisorption, small and wide (2 θ) angle XRD patterns, FT-IR, SEM and HRTEM. The acidic properties of the hybrid material were studied by cumene dealkylation and those of the catalyst were studied by FT-IR of adsorbed pyridine. The catalyst, Pt/HMFI–SBA-15, was tested for tetralin transformation at various reaction temperatures 498, 523, 548, 573, 585 and 598 K. Wide-angle XRD and FT-IR in the skeletal region indicate the presence of MFI zeolite fragments incorporated onto SBA-15. The characterization of the acid sites on the support by cumene dealkylation and FT-IR pyridine adsorption revealed the presence of Brönsted acid sites related to the HMFI zeolite fragments in the hybrid materials. For the catalyst, a homogeneous distribution of Pt clusters was found by HRTEM. In the transformation of tetralin, at all the reaction temperatures, the main products were trans + cis-decalins. However, at high reaction temperature ring contraction to spirodecane and dehydrogenation to naphthalene were observed. At 598 K, a maximum of 8% of ring contraction products was obtained.

Silylene-Mediated Ring Contraction of Homoallylic Ethers To Form Allylic Silanes

(-)-Isopulegol derivatives undergo a ring contraction under silylene-mediated conditions to provide cyclopentane products. Silylene transfer to other homoallylic ethers did not provide the ring contraction products. Allylic silane products were elaborated to determine the stereochemical course of the ring contraction reaction. A mechanism for the transformation is proposed.

Study of Ir/WO 3/ZrO 2–SiO 2 ring-opening catalysts: Part II. Reaction network, kinetic studies and structure–activity correlation

The present paper is the second part of a systematic study of the influence of W and Ir loading on the activity of Ir/WO 3/ZrO 2–SiO 2 catalysts for the ring-opening reaction of naphthenic molecules using methylcyclohexane (MCH) as a model compound. A series of Si-stabilized tungstated zirconias, WO x /ZrO 2–SiO 2, containing up to 3.5 atom W/nm 2, was prepared. Ir-based catalysts containing up to 1.2 wt% were obtained by impregnation of these solids. Characterization of the metal dispersion and catalyst acidity was described in a previous article. The objective of the present study was to determine the best metal/acid balance for optimal performance of Ir/WO x /ZrO 2–SiO 2 catalysts in the ring-opening reaction of MCH. Monofunctional (acid WO x /ZrO 2–SiO 2 or metal Ir/ZrO 2–SiO 2) and bifunctional (Ir/WO 3/ZrO 2–SiO 2) catalysts were examined. Based on the analysis of the yields and products distributions, a reaction network was proposed, and kinetic data (e.g., activation energies, initial rates) were calculated. Correlations between characterization results obtained earlier (e.g., acidity, dispersion) and catalytic performance are also reported. The monofunctional acid catalysts WO x /ZrO 2–SiO 2 showed a low selectivity for ring opening. The ring-contraction activity developed for W surface density above a threshold value of 1 atom W/nm 2. This was attributed to the appearance and the development of a relatively strong Brönsted acidity monitored by infrared measurements. MCH ring contraction and C5 naphthene ring opening occur according to a classic acid mechanism. For low conversions, the monofunctional metal catalysts Ir/ZrO 2–SiO 2 exhibited significant selectivity for ring opening that decreased with increasing conversion. Because of the lack of ring-contraction products, the observed activity was attributed to the direct ring opening of the MCH. Ring opening and cracking occur according to a dicarbene mechanism. The study of MCH conversion on Ir/WO x /ZrO 2–SiO 2 catalysts indicated that MCH ring contraction to alkylcyclopentanes occurs before ring opening. The best yields for ring opening were obtained with the 1.2% Ir/WO x /ZrO 2 (1.5 atom of W/nm 2). Further increases in W surface density led to a decrease in the indirect ring-opening yield, attributed to a decrease in Ir dispersion. For bifunctional metal/acid catalysts, analysis of the mechanism is less straightforward. The activation energy for C6 ring contraction and indirect C6 ring opening is a function of the metal/acid ratio. For high ratios, indirect ring opening occurs essentially over metallic sites. A decrease in the metal/acid ratio enhances the contribution of acid mechanism.

The effect of sulfur compound on the hydrogenation of tetralin over a Pd–Pt/HDAY catalyst

A composite metal catalyst with a Pd/Pt of 4:1 and an H-form dealuminated Y zeolite support for the hydrogenation of tetralin was investigated. The materials were characterized by XRD, NH3-TPD, N2 adsorption, TPR and FTIR. The activity for the hydrogenation of tetralin was investigated with a high-pressure fixed-bed continuous-flow reactor operating at 4.0 MPa. The thiotolerance was tested with feeds containing 200 ppm sulfur in the form of 4,6-dimethyldibenzothiophene and thiophene, respectively. It was found that thiophene was more effective for deactivating the catalyst than the former one. The diffusion barrier of the pores for the sulfur compound is likely the major reason for the different deactivation rate of catalysts. The products other than decalins were mainly decalin isomers and ring-opened products. Selectivity of cracking products for the feed with thiophene was lower than that for the other feed, while that of ring-opened and ring-contracted products with the two feeds was similar. © 2007 Elsevier B.V. All rights reserved.

Syntheses and Reactivity of meso-Unsubstituted Azuliporphyrins Derived from 6-tert-Butyl- and 6-Phenylazulene

A series of six azuliporphyrins with substituents on the seven-membered ring were prepared by two different "3 + 1" routes from 6-tert-butyl- and 6-phenylazulene. The substituted azulenes can be converted into dialdehydes under Vilsmeier-Haack conditions, and these react with tripyrranes in the presence of TFA in CH2Cl2 to give azuliporphyrins in excellent yields. Alternatively, tripyrrane analogues can be prepared by reacting the substituted azulenes with an acetoxymethylpyrrole in the presence of acetic acid, and following a deprotection step, these condensed with a pyrrole dialdehyde to give the related azuliporphyrins in 45-51% yield. Five of the azuliporphyrins were sufficiently soluble in CDCl3 to afford high-quality proton and carbon-13 NMR data. The internal CH and NH resonances were observed near 3 ppm, although the precise values were dependent upon substituent effects. The presence of a tert-butyl group on the azulene moiety slightly enhanced the diatropicity of the macrocycle compared to the phenyl-substituted azuliporphyrins. Polar solvents also increased the downfield shifts to the external protons by stabilizing the dipolar resonance contributors that are responsible for the carbaporphyrinoid aromatic character. A tert-butyl-substituted azuliporphyrin also gave X-ray quality crystals, and this allowed the first structural analysis of a free base azuliporphyrin to be conducted. The macrocycle is near planar, and the azulene unit was only tilted out of the plane by 7.4 degrees. An analysis of the bond lengths suggests that a 17 atom delocalization pathway significantly contributes to the aromatic properties of this system. Protonation of azuliporphyrins affords dications with enhanced diamagnetic ring currents where the internal CH shifts to ca. -3 ppm. Again, the chemical shifts are influenced by the substituents and the presence of an electron-donating tert-butyl group on the azulene subunit increases the macrocyclic diatropicity. Two of the substituted azuliporphyrins were reacted with nickel(II) acetate or palladium(II) acetate in DMF to give the corresponding organometallic derivatives, and these stable complexes were isolated in excellent yields. Addition of pyrrolidine to NMR solutions of 23-substituted azuliporphyrins 19 demonstrated that nucleophilic addition products were present in equilibrium with the parent porphyrinoids, but these adducts are less favored than for azuliporphyrins lacking the 23-substituents. Although nucleophilic attack of a peroxide anion is believed to be the first step in the conversion of azuliporphyrins to benzocarbaporphyrins with t-BuOOH and KOH, the tert-butyl or phenyl substituents in azuliporphyrins 19a and 19b did not inhibit this chemistry. Two benzocarbaporphyrin products were isolated and characterized in each case, and mechanisms are proposed to explain the origins of these oxidative ring contraction products.

Thallium(III)-Mediated Ring Contraction of cis-Octalins: An Approach for the Diastereoselective Construction of the nor-Bakkane Skeleton

A new approach for the diastereoselective synthesis of cis-hydrindanes bearing important structural features of the bakkane skeleton is described. The key step in such a sequence is a thallium trinitrate mediated oxidative rearrangement of cis-octalins. The ring-contraction products thus obtained were elaborated in a diastereoselective fashion into hydrindanes bearing a quaternary center.

Further Investigation on the Rearrangement Mechanism of Reactions of 1,5-Benzothiazepines with Ethoxycarbonylcarbene

The reactions of 2,3-dihydro-1, 5-benzothiazepines with ethoxycarbonylcarbene undergo complex rearrangements to produce ring-opening and ring contraction products. Previously it was presumed that the different products were formed via different mechanisms depending on the kind of substituents at the 2-position of 1, 5-benzothiazepines. However, on the basis of the further detailed investigation, it was found that all 1,5-benzothiazepines can undergo the same rearrangement to yield both ring-opening and ring contraction products.

Electrophilic Behavior of the π Delocalized Azepinium Ion: Friedel−Crafts Reactions with Benzenes and Five-Membered Aromatic Heterocycles

[reaction: see text] Although the reactivity of tropylium ion with aromatic substrates is low, the reaction of azepinium ion with aromatic substrates such as benzene, phenol, furan, and thiophene resulted in the formation of 2-aryl-2H-azepine as a major product. An exceptional result in the formation of ring-contracted product was observed in the reaction with pyrrole.

A Fast and Efficient Route to 5-Chloromethyl-1,4,7,10-Tetrathiacyclotridecane and its Behavior in a Chloroform Solution

Chlorination of [14]aneS4-ol (1,4,8,11-tetrathiacyclotetradecan-6-ol) by a one pot reaction in 3 min produces quantitatively the ring-contracted product [13]aneS4-CH2Cl (5-chloromethyl-1,4,7,10-tetrathiacyclotridecane). In a chloroform solution, [13]aneS4-CH2Cl is slowly converted to an isomer [14]aneS4-Cl (6-chloro-1,4,8,11-tetrathiacyclotetradecane) until an equilibrium takes place. These results are discussed and a reaction mechanism involving an episulfonium ion intermediate is proposed.

A novel boron trifluoride etherate mediated deep-seated rearrangement of an α,β-epoxyketone

Acid catalysed reaction of carvone epoxide 2 resulted in dimeric products 3 and 4, in contrast to the expected ring contraction product. Reaction of β-methylcarvone epoxides 8 and 11 with acids furnished 2-acetyl-4-isopropenylcyclopentanones 9 and 14 containing a stereodefined quaternary carbon atom. On the other hand, the reaction of epoxides 8 and 11 with boron trifluoride etherate lacks the stereoselectivity and in addition, anti-epoxide 8 furnished lactone 18 via an unusual deep seated rearrangement.

Facile Synthesis of 4‐Alkyl (and Aryl)‐2‐aryl‐6‐diazo‐4H‐thieno[3,2‐b]pyridine‐5,7‐diones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Facile synthesis of 4-alkyl (and aryl)-2-aryl-6-diazo-4h- thieno[3,2-b]pyridine-5,7-diones.

Treatment of 3-[3-alkyl (and aryl)amino-5-arylthieno-2-yl]-2-diazo-3-oxopropanoates 8 with TMSOTf (3 equiv) in the presence of Et(3)N (6 equiv) in CH(2)Cl(2) for 1 h at room temperature afforded 4-alkyl (and aryl)-2-aryl-6-diazo-4H-thieno[3,2-b]pyridine-5,7-diones 14 in excellent yields. On heating of 14 in the presence of a catalytic amount of Rh(2)(CF(3)CF(2)CF(2)CO(2))(4) in PhH for 4-10 h at reflux, corresponding ring contraction products, 4-alkyl (and aryl)-5,6-dihydro-4H-thieno[3,2-b]pyrrol-5-ones 16, were produced in good to excellent yields.

Rearrangement of 2-quinolyl- and 1-isoquinolylcarbenes to naphthylnitrenes.

2-quinolylcarbene 23 and 1-isoquinolylcarbene 33 are generated by flash vacuum thermolysis (FVT) of the corresponding triazolo[1,5-a]quinoline and triazolo[5,1-a]isoquinoline 19 and 29, as well as 2-(5-tetrazolyl)quinoline and 1-(5-tetrazolyl)isoquinoline 20 and 30, respectively. These carbenes rearrange to 1- and 2-naphthylnitrene 21 and 31, respectively, and the nitrenes are also generated by FVT of 1- and 2-naphthyl azides 18 and 28. The products of FVT of both the nitrene and carbene precursors are the 2- and 3-cyanoindenes 26 and 27 together with the nitrene dimers, viz. azonaphthalenes 25 and 35, and the H-abstraction products, aminonaphthalenes 24 and 34. All the azide, triazole, and tetrazole precursors yield 3-cyanoindene 26 as the principal ring contraction product under conditions of low FVT temperature (340-400 degrees C) and high pressure (1 Torr N(2) as carrier gas for the purpose of collisional deactivation). This ring contraction reaction is strongly subject to chemical activation, which caused extensive isomerization of 3-cyanoindene to 2-cyanoindene under conditions of low pressure (10(-3) Torr). 2-Cyanoindene is calculated to be ca. 1.7 kcal/mol below 3-cyanoindene in energy; accordingly, high-temperature FVT of these cyanoindenes always gives mixtures of the two compounds with the 2-cyano isomer dominating. Photolysis of trizolo[1,5-a]quinoline 19 and triazolo[5,1-a]isoquinoline 29 in Ar matrixes causes partial ring opening to the corresponding 2-diazomethylquinoline 19' and 1-diazomethylisoquinoline 29'. The photolysis of the former gives rise to a small amount of the cyclic ketenimine 22, the intermediate connecting 2-quinolylcarbene and 1-naphthylnitrene.

Barton–Kellogg olefination of conjugated dithioxo compounds

The first Barton–Kellogg olefination employing thioamides or thioureas as substrates is reported. Starting from the conjugated dithioxo compounds 1 and diazocompounds 2 we substituted the C˭S groups by ester substructures mono- (type 3) and obtained the disubstituted products 4. Using the same procedure, the tricyclic thiourea 5 was converted into a new ketene aminal 6. Intermediates such as primary cycloadducts or three-membered ring-contraction products could not be isolated for any reactions studied here.

Synthesis, characterisation and coordinating properties of the small ring S2Te-donor macrocycles [9]aneS2Te, [11]aneS2Te and [12]aneS2Te

The reaction of Na2Te with various α,ω-dichlorodithioether reagents in thf–NH3(l) at ca. −78 °C produces moderate yields of the [1+1] cyclisation products, [9]aneS2Te (1,4-dithia-7-telluracyclononane), [11]aneS2Te (1,4-dithia-8-telluracycloundecane) and [12]aneS2Te (1,5-dithia-9-telluracyclododecane), together with polymer. These new small ring macrocycles may be purified by flash column chromatography on silica (11-and 12-membered rings) or by recrystallisation from MeOH–thf (9-membered ring), affording yellow waxy solids. The products have been characterised by NMR (1H, 13C{1H} and 125Te{1H}) and IR spectroscopy, mass spectrometry and the crystal structures of [11]aneS2Te and [12]aneS2Te have been obtained. The more stable organo-Te(IV) derivatives [n]aneS2TeI2 (n = 11 or 12) and [n]aneS2TeMeI (n = 9, 11 or 12) are obtained in high yield as powdered solids by reaction with I2 or MeI and these have been characterised similarly. A crystal structure of [12]aneS2TeI2 has also been determined and is compared with the parent macrocycle. The synthesis of [9]aneS2Te is more sensitive to the precise reaction conditions than the others, and is accompanied by the formation of the ring-contraction products 1-thia-4-telluracyclohexane and 1,4-dithiane. These too have been characterised by NMR and IR spectroscopy and by mass spectrometry. The former has been unambiguously identified by X-ray crystallography and its Te(IV) methiodide derivative has been prepared for comparison. The ligating properties of the new dithiatellura-macrocycles have been investigated with a variety of transition metal species giving fac-[Mn(CO)3(L)]CF3SO3, cis-[MCl2(L)] (M = Pd or Pt), [Rh(Cp*)(L)](PF6)2, [Cu(L)]BF4 and [Ag(L)]CF3SO3. Where possible, the mode of coordination has been established by spectroscopic methods, ring-size effects established and the data compared with other complexes incorporating related cyclic and acyclic ligands.

Thallium Trinitrate Mediated Oxidation of 3‐Alkenols: Ring Contraction vs Cyclization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactions of Trifluoromethylsulfenyl Chloride and Trifluoromethylthiocopper with 2-(Trimethylsilyl)thiazole

The treatment of 2-(trimethylsilyl)thiazole with trifluoromethylsulfenyl chloride furnishes the expected 2-(trifluoromethylthio)thiazole in satisfactory yields along with the ring contraction product of the azirine-type. However, the reaction of 2-bromothiazol with trifluoromethylthiocopper gives poor yields of the above compound. The mechanism of formation and the mass spectral characterization of the products are presented in this article.

The Effect of Protecting Groups on Thallium(III)‐Promoted Ring Contraction of 3‐Alkenols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Biological consequences of free radical-damaged DNA bases 1,2

The principal oxidized cytosine bases, uracil glycol, 5-hydroxycytosine, and 5-hydroxyuracil, are readily bypassed, miscode, and are thus important premutagenic lesions. Similarly the principal oxidation product of guanine, 8-oxoguanine, miscodes with A and is a premutagenic lesion. Most of the thymine and adenine products that retain their ring structure primarily pair with their cognate bases and are not potent premutagenic lesions. Although thymine glycol pairs with its cognate base and is not mutagenic it significantly distorts the DNA molecule and is a lethal lesion. Ring fragmentation, ring contraction, and ring open products of both pyrimidines and purines block DNA polymerases and are potentially lethal lesions. Although these breakdown products have the potential to mispair during translesion synthesis, the mutational spectra of prokaryotic mutants defective in the pyrimidine-specific and/or purine-specific DNA glycosylases do not reflect that expected of the breakdown products. Taken together, the data suggest that the principal biological consequences of endogenously produced and unrepaired free radical-damaged DNA bases are mutations.

Optimization of ring-contraction of the meso enedione epoxide for chiral building block synthesis

The ring-contraction of the enedione epoxide obtained from the adduct of benzoquinone and cyclopentadiene is mainly affected by the amount of base used. Excellent yields (>80%) of the ring-contracted product were consistently obtained when the epoxide was treated with a 0.5 equiv. of ethanolic sodium hydroxide in ethanol. The versatility of the chiral building block accessible from the ring-contracted product has also been demonstrated by an alternative diastereocontrolled synthesis of (+)-tanikolide, a toxic and antifungal marine natural product isolated from Lyngbya majuscula.