Synthesis of haloconduritols from an endo-cycloadduct of furan and vinylene carbonate

A method for preparing haloconduritols having a conduritol-A construction is described. A mixture of endo- and exo-cycloadduct derivatives prepared from the Diels-Alder reaction of furan and vinylene carbonate was converted into diacetate derivatives by hydrolysis (K₂CO₃/MeOH) followed by acetylation (Ac₂O/pyridine). Boron trihalide (BBr₃ or BCl₃)-assisted ring-opening of the endo-diacetate in CH₂Cl₂ at −78°C gave (1α,2α,3β,6β)-6-halogeno-4-cyclohexene-1,2,3-triol 1,2-diacetate from which the corresponding triacetate was prepared by acetylation (AcCl). trans-Esterification of the triacetate (MeOH/HCl) afforded (1α,2α,3β,6β)-6-halogeno-4-cyclohexene-1,2,3-triol (X=Br or Cl). BF₃-Assisted ring-opening of the endo-diacetate in CH₂Cl₂ gave (1α,2α,3β,6β)-6-chloro-4-cyclohexene-1,2,3-triol 1,2-diacetate by means of halogen exchange.     

Synthesis of furan from allenic sulfide derivatives

In this paper, we report the synthesis of furan derivatives from allenic sulfides. By the reaction with NaH, β-Hydroxyl allenic sulfides were found to generate furan products in excellent yields with the removal of phenylthio group. β-Aldehyde allenic sulfides were found to give similar furan products with one more substituent when treated with additional nucleophilic reagents. β-ketone allenic sulfides can also cyclize to give furan derivatives with the promotion of P₂O₅.     

Synthesis of 2,5-diethyl-3,4-bis(trifluoromethyl)furan and its derivatives

The addition reaction of propionaldehyde to hexafluoro-2-butyne ( 1 ) under γ-ray irradiation gave trans-6,6,6-trifluoro-4-trifluoromethyl-4-hexen-3-one ( 2 ) and 4,5-bis(trifluoromethyl)octa-3,6-dione ( 3 ). The latter compound was treated with sulfuric acid to give 2,5-diethyl-3,4-bis(trifluoromethyl)furan ( 4a ). Several reactions, such as bromination, dehydrobromination and oxidation, were carried out to prepare derivatives of 4a .     

A Convenient Route for the Synthesis of 4-Aryl- and 4-Aminopyrimidines

Summary. A series of ureidopropenenitriles were synthesised by Knoevenagel condensation of ArCOCH₂CN and HC(OEt)₃ in presence of ureas in a one pot reaction. These ureidopropenenitriles were cyclised to 4-aryl-5-cyano-3-substituted pyrimidines (in acid) or to 4-amino-5-benzoylpyrimidines (in base) in 60–70% yields. The amine pyrimidine derivatives were further converted to substituted uracils by hydrolysis with isopentyl nitrite in DMF. Alkylation of uracils furnished 1,3-dimethyluracil derivatives with DMS in alkali. All new compounds were characterised by spectral and analytical methods.     

A Convenient Route for the Synthesis of 4-Aryl- and 4-Aminopyrimidines

A series of ureidopropenenitriles were synthesised by Knoevenagel condensation of ArCOCH₂CN and HC(OEt)₃ in presence of ureas in a one pot reaction. These ureidopropenenitriles were cyclised to 4-aryl-5-cyano-3-substituted pyrimidines (in acid) or to 4-amino-5-benzoylpyrimidines (in base) in 60–70% yields. The amine pyrimidine derivatives were further converted to substituted uracils by hydrolysis with isopentyl nitrite in DMF. Alkylation of uracils furnished 1,3-dimethyluracil derivatives with DMS in alkali. All new compounds were characterised by spectral and analytical methods.     

DFT Studies on the addition reaction between germylene and furan

The mechanism of the addition reaction of germylene H₂Ge and furan has been investigated with B3LYP/6-311+G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. From the surface energy profile, it can be predicted that there are four reactions (1)–(4). Reactions (1) and (2) are similar, which are reactions between H₂Ge and C=C of isolated furan. Furthermore, H₂Ge can react with oxygen atom of furan to form a stable complex H₂Ge-Furan. Reactions (3) and (4) are similar, which are reactions between H₂Ge and C=C of the complex H₂Ge-Furan. All the reactions consist of two steps: the two reactants first form an intermediate (INT) through a barrier-free exothermic reaction; this intermediate then isomerizes to a product (P) via a transition state (TS). The article is published in the original.     

Dinuclear palladium(I) sandwich complexes of furan and toluene

The reaction of a dinuclear palladium complex [Pd₂(CH₃CN)₆][X]₂ (X = BF₄, PF₆) with excess furan afforded the sandwich-type bis-furan dinuclear palladium(I) complex [Pd₂(μ-furan)₂(CH₃CN)₂][X]₂. The substitutionally labile bridging furan ligands in the dipalladium sandwich complex can be readily replaced with toluene to give the bis-toluene dipalladium(I) sandwich complex [Pd₂(μ-toluene)₂(CH₃CN)₂][X]₂.     

Synthesis of spirocyclic azacycles from the cyclization of furan tethered N-acyliminium ions

The protic and Lewis acid promoted cyclization reactions of tethered furan-4,5-dihydroxypiperid-2-ones, furan-4,5-diacetoxypiperid-2-ones and furan-3,4-diacetoxypyrrolid-2-ones, via their corresponding N-acyliminium ion intermediates, have been studied. In the case of the furan-4,5-dihydroxypiperid-2-one 2a and its diacetate derivative 2b, macrocyclic products were formed from an initial intermolecular reaction between 2a or 2b, via the nucleophilic C5 furan carbon, and their corresponding N-acyliminium ion intermediates. When the furan C5 position of 2b was blocked by substitution with bromine then TFA or Sc(OTf)₃ catalysed cyclization reactions gave a spirotricyclic product (a 5-6-6-tricycle) in a highly diastereoselective manner. Cyclization of the analogous C5-Br-furan-pyrrolidone 29 with TFA resulted in a related spirotricyclic (a 5-6-5 tricycle) product. Attempts to prepare an analogous azepine system, a 5-7-5 tricycle, were not successful. Cyclization reactions of the C5-PhS-furan- or C5-phenylsulfonyl-pyrrolidone analogues of 29 with TFA were also not successful.     

Novel condensed heterocyclic derivatives of benzofuran based on 2,5-dihydroxy-3,4,6,7tetrachloro-2, 3-dihydrobenzo[b]furan

We have synthesized novel condensed heterocyclic derivatives of benzofuran by reaction of 2,5-dihydroxy3, 4, 6, 7-tetrachloro-2, 3-dihydrobenzo[b]furan (I) with 4-phenyl- and 4-methylthiosemicarbazides, diphenylthiocarbazone, and also via cyclization of 2, 5-dihydroxy-4, 6, 7-trichloro-3-(N, N-diethyldithio-carbarnoyl)-2, 3dihydrobenzo[b]furan (obtained in the reaction of benzofuran I with sodium NN-dithiocarbamate).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 463467, April 1996.     

In-bulk formation of a new tetrasubstituted furan from phenolic antioxidants and dibasic lead stearate

The reaction between octadecyl 3-(3,5-di-tert-4-hydroxyphenyl)propanoate and dibasic lead stearate, two compounds added in most PVC formulations, has been investigated in bulk. The structure of the resulting product, obtained after a one-pot synthesis, was characterized by HRMS and 2D NMR analyses. The product of empirical formula C₇₀H₁₁₆O₇ has been identified as an unknown highly substituted furan. The reaction mechanism between both products to produce this original furan has been established. The first step leads to a discoloured lead IV complex with bis-quinonemethide. The second step consist of a hydrolysis during the solvent extractions or under UV exposure leading to a tetrasubstituted furan.     

Transition metal-free cross-coupling of furan ring with haloacetylenes

On the example of menthofuran, a naturally abundant compound, it has been shown for the first time that the furan ring can be readily cross-coupled with acylhaloacetylenes in the solid Al₂O₃ powder at room temperature to afford the corresponding 2-ethynyl derivatives in up to 88% yield. The reaction represents a ring closing/ring opening process that includes reversible formation of the intermediate cycloadducts further producing acetylene derivatives with elimination of HHal.     

Formation of 1,2,5‐Oxadiazole,Isoxazole, Isothiazole, 1,2,3‐Triazole,and Pyrrole Rings from N‐(5,5‐Dimethyl‐3‐oxocyclohexenyl)‐S,S‐diphenylsulfilimine

Reactions of N‐(5,5‐dimethyl‐3‐oxocyclohexenyl)‐S,S‐diphenylsulfilimine, a kind of enaminone, with isopentyl nitrite, isocyanates, isothocyanates, benzenediazonium chloride, and 1,1,1‐trifluoro‐4‐ethoxy‐3‐buten‐2‐one gave 1,2,5‐oxadiazole, isoxazole, isothiazole, 1,2,3‐triazole, and pyrrole derivatives condensed with cyclohexane, respectively, in one pot.     

Rate coefficients for the gas-phase OH + furan (C4H4O) reaction between 273 and 353 K

Rate coefficients, k₁, for the gas-phase OH radical reaction with the heterocyclic ether C₄H₄O (1,4-epoxybuta-1,3-diene, furan) were measured over the temperature range 273–353 K at 760 Torr (syn. air). Experiments were performed using: (i) the photochemical smog chamber THALAMOS (thermally regulated atmospheric simulation chamber, IMT NE, Douai-France) equipped with Fourier Transform Infrared (FTIR) and Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) detection methods and (ii) a photochemical reactor coupled with FTIR spectroscopy (PCR, University of Crete, Greece). k₁(273–353 K) was measured using a relative rate (RR) method, in which the loss of furan was measured relative to the loss of reference compounds with well-established OH reaction rate coefficients. k₁(273–353 K) was found to be well represented by the Arrhenius expression (1.30 ± 0.12) × 10⁻¹¹ exp[(336 ± 20)/T] cm³ molecule⁻¹ s⁻¹, with k₁(296 K) measured to be (4.07 ± 0.32) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The k₁(296 K) and pre-exponential quoted error limits are 2σ and include estimated systematic errors in the reference rate coefficients. The observed negative temperature dependence is consistent with a reaction mechanism involving the OH radical association to a furan double bond. Quantum mechanical molecular calculations show that OH addition to the α-carbon (ΔH_r(296 K) = −121.5 kJ mol⁻¹) is thermochemically favored over the β-carbon (ΔH_r(296 K) = −52.9 kJ mol⁻¹) addition. The OH-furan adduct was found to be stable over the temperature range of the present measurements. Maleic anhydride (C₄H₂O₃) was identified as a minor reaction product, 3% lower-limit yield, demonstrating a non-ring-opening active reaction channel. The present results are critically compared with results from previous studies of the OH + furan reaction rate coefficient. The infrared spectrum of furan was measured as part of this study and its estimated climate metrics are reported.     

Theoretical investigation of unimolecular decomposition channels of furan4

Density functional theory and high-level ab initio calculations were carried out to investigate three unimolecular decomposition channels of furan. All equilibrium and transition state structures along the proposed decomposition channels are fully optimized by B3LYP/6-31G** and characterized at the same level of theory by vibrational and intrinsic reaction coordinate analyses. Relative energies of the optimized structures were evaluated at theoretical levels up to QCISD(T)/6-311++G**. The theoretical results suggest that the unimolecular decomposition channel of isoxazole, proposed in an experimental study and implied to be the main decomposition channel of furan, is responsible only for the formation of HC(TRIPLE BOND)CH and H₂O(DOUBLE BOND)C(DOUBLE BOND)O, minor products of furan thermal decomposition. A new decomposition mechanism, proposed in the present study, is shown to be more likely responsible for the formation of CH₃C(TRIPLE BOND)CH and CO, major products of furan thermal decomposition. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 240–249, 1998     

Organosilicon compounds of the furan series. VI. Nitrogen- and sulfur-containing organosilicon derivatives of furan

Five new furfurylaminoorganylsilanes and furfurylaminoalkyltriorganylsilanes are synthesized by reacting furfurylamine with organylchlorosilanes, chloroalkyltriorganylsilanes, and triorganylhydrosilanes. Furfuraldoxime readily reacts with triorganylchlorosilanes in the presence of triethylamine to give O-triorganylsilyl substituted oximes. It is shown for the first time that in the presence of H₂PtCl₆ aldoximes undergo dehydrocondensation with triorganylsilanes, accompanied by reduction processes. Reaction of hexamethyldisilazane with pyromucamide gives the trimethylsilylamide. Pyromuconitrile and magnesium 3-(methyldiethylsilyl)propyl chloride gives 1-furyl-4-(methyldiethylsilyl)butanone-1. Reaction of organylchlorosilanes with furfurylmercaptan and sodium furfurylmercaptide permits synthesis of the first representatives of the sulfur-containing organosilicon derivatives of furan.Part V, see [1].     

Sodium borohydride or potassium carbonate-mediated intramolecular Michael addition: a general method for the synthesis of fused dihydrofuran and furan derivatives

A simple and convenient method for the synthesis of fused dihydrofuran derivatives using NaBH₄-mediated reductive cyclization and fused furan derivatives by K₂CO₃-mediated intramolecular Michael addition followed by acid-catalyzed methanol elimination has been developed.     

Reactions of furan derivatives with aliphatic carbonyl compounds in acid medium

Sixteen new derivatives of the furan and of the 1,1-difurylmethane series were synthesized by the reactions of furan, 2-methylfuran, 2-(3′-acetoxypropyl)furan, 2-(3′-butyl)furan, 1-cyclopropyl-2-αfurylcyclopropane, and 1,1-difurylethane with saturated and α, β-unsaturated aliphatic carbonyl compounds in acid medium.     

1,3-Dipolar cycloadditions of heterocycles 1. Cycloadditions ofC-benzoyl-N-phenylnitrone to furan

A frontier orbital treatment of furan suggests its possible reactivity in 1,3-dipolar cycloadditions with dipoles posessing low lying LUMO's, such as nitrones, especially those with electronwithdrawing substituents. By the reaction ofC-benzoyl-N-phenylnitrone1a with an excess of furan at 60° the monocycloadduct2a, two biscycloadducts4 and5 and further reaction products of nitrone such as azoxybenzene8, diketoamide9a, benzoanilide10a, benzoic acid11a and phenyl glyoxylic acid12 were isolated. The cycloaddition ofC-(4-bromobenzoyl)-N-phenylnitrone1b with furan is also reported.Part CXXXVI in the series Furan Derivatives; Part CXXXV: Coll. Czech. Chem. Commun., in press.     

Conformational analysis of furan and thiophen carbonyl derivatives

The 220 MHz NMR spectra of furan and thiophen carbonyl compounds were measured, and further investigated by benzene solvent shifts, induced chemical shifts by the lanthanide shift reagent Eu(FOD)₃; and by the Nuclear Overhauser effect.Two planar isomers of the furan derivatives exist in the ratio of ca. 1:1·05 ～ 1:1·18 (cis/trans), while the cis form of thiophen derivatives is favoured. Semi-empirical calculations (CNDO/2) are reported and the influence of sulfur 3d-orbitals are discussed.     

Highly efficient chiral resolution and determination of absolute configuration of 2-alkanols by using a cyclopenta[b]furan derivative

The reaction of 3a-benzhydryl-3,3a,4,5-tetrahydro-2H-cyclopenta[b]furan and various 2-alkanols in the presence of a catalytic amount of pyridinium 4-tolunesulfonate in dichloromethane gave 3a-benzhydryl-6a-(1-methyl-aloxy)-hexahydrocyclopenta[b]furan in more than 90% chemical yields. The resulting diastereomeric mixture is easily separable on silica gel chromatography because of the large ΔR_f value (briefly 0.1). Absolute configuration of the 2-alkanols can be easily estimated by the chemical shifts of ¹H and ¹³C NMR of methyne group of the benzhydryl moiety.