An unexpected oxidative decarboxylation reaction of 2,3-dihydroxybenzoic acid in the synthesis of new dibenzyltetrahydroquinoxalinediones

Chemical and electrochemical oxidation of different catechols were carried out in the presence of N,N′-dibenzylethylenediamine (DBEDA) in a phosphate buffer/acetonitrile solution for the synthesis of different new dibenzyltetrahydroquinoxalinedione derivatives. The oxidation of catechol (1a), 2,3-dihydroxybenzoic acid (1e), and 3,4-dihydroxybenzoic acid (1d) led to the same product, probably due to the decarboxylation reaction of intermediates. An oxidative decarboxylation reaction of 3,4-dihydroxybenzoic acid (1d) has been reported before, while an unexpected oxidative decarboxylation reaction of 2,3-dihydroxybenzoic acid (1e) in the presence of DBEDA is reported for the first time.     

Synthesis and properties of tetraphenyltriafulvene

The reaction of the 1,2-diphenylcyclo propenium ion (5) with benzhydrylmagnesium bromide exclusively affords 1,2-diphenyl-3-benzhydrylcyclo propene (4), though the reaction of 5 with benzhydryllithium in the presence of lithium chloride yields no cyclopropene 4 but 1,3-diphenyl-3-benzhydryl-cyclopropene (6) via the intermediate formation of 1,2-diphenyl-3-chlorocyclopropene (7). The hydride abstraction from the cyclopropene 4 followed by deprotonation gives tetraphenyltriafulvene (2) as dark red crystals. The ¹³C NMR spectrum, as well as a bathochromic shift of the longest-wavelength absorption in the electronic spectrum with decrease in solvent polarity, indicates a considerable contribution of the dipolar structure at the ground state of 2. The cyclic voltammetry on 2 reveals that 2 can be readily oxidized to a stable cation radical and a less stable dication. The cation radical was also generated by chemical oxidation with silver tetrafluoroborate or antimony pentafluoride, and was investigated by ESR spectroscopy.     

The highly stereoselective decarboxylation of (+)-1-bromo-1-chloro-2,2,2-trifluoropropanoic acid to give (+)-1-bromo-1-chloro-2,2,2-trifluoroethane [(+)-halothane] with retention of configuration

The absolute configuration of the title acid 2 has been determined to be S by X-ray crystallography. Thus, decarboxylation of 2 produces (S)-(+)-halothane with 99% retention of configuration. This behavior is compared to other stereoselective decarboxylation reactions of α-haloacids from the literature that also gave high degrees of retention of configuration when in the form of their quaternary ammonium salts, which contain one proton. The proton of the ammonium salt is necessary in order to protonate the anionic intermediate formed from decarboxylation. In the absence of this relatively acidic proton, we had previously found that using triethylene glycol (TEG) as both the solvent and proton source for the decarboxylation reaction of acid 2 caused poor stereoselectivity. This was in contrast to 1,2,2,2-tetrafluoro-1-methoxypropionic acid 6, which showed a high degree of retention of configuration in TEG. In order to rationalize this differing behavior, we report DFT studies at PCM-B3LYP/6-31++G⁷ level of theory (the results were additionally confirmed with 6-311++G⁷ and aug-cc-pVDZ basis sets). The energy barrier to inversion of configuration of the anionic reaction intermediate 11 of acid 2 is 10.23 kcal/mol. However, we find that the anionic intermediate 10 from acid 6 would rather undergo β-elimination instead of inversion of configuration. Thus the planar transition state required for inversion of configuration is never reached, regardless of the rate of proton transfer to the anion.     

A general method for one-step synthesis of monofluoroiodane(III) reagents using silver difluoride

Herein we report a new general method for one-step synthesis of four kinds of fluoroiodane(III) reagents by treating the corresponding aryl iodides with silver difluoride (AgF₂). This is the first method applicable for the synthesis of all four fluoroiodane(III) reagents including p-iodotoluene difluoride (1), fluoro-benziodoxole (2), fluoro-benziodoxolone (3), and fluoro-N-acetylbenziodazole (4). AgF₂ was firstly employed in the direct oxidative fluorination of iodobenzene and thus has shown its outstanding oxidation and fluorine-transfer ability. The use of AgF₂ has improved the synthesis of fluoroiodane(III) reagents by shortening the reaction steps, avoiding the use of hazardous reagents, and simplifying the experimental operations. It was worth noting that we have developed the first one-step direct synthetic method for 3, while 3 can only be synthesized through Cl→F ligand exchange reaction previously.     

N-tert-Butylbenzenesulfenamide-catalyzed oxidation of alcohols to the corresponding carbonyl compounds with N-chlorosuccinimide

N-tert-Butylbenzenesulfenamide (1)-catalyzed oxidation of various primary and secondary alcohols to the corresponding aldehydes and ketones was efficiently carried out by using N-chlorosuccinimide (NCS) in the coexistence of potassium carbonate and molecular sieves 4 Å at easy-to-control temperatures ranging from 0°C to room temperature. The present catalytic oxidation was performed without giving any damage to the functional groups in alcohols, and was particularly effective in the oxidation of alcohols that formed labile aldehydes because of its mild reaction conditions. Further, selective oxidation of primary hydroxy groups took place in 1-catalyzed oxidation of several diols. Mechanistic investigation suggested that the chlorination of the sulfenamide 1 by NCS led to the formation of a key species, N-tert-butylbenzenesulfinimidoyl chloride (2), which in turn oxidized alcohols in the presence of potassium carbonate to afford carbonyl products by accompanying regeneration of the catalyst 1.     

Stereochemistry and reactivity of F- and H-vinyldiazocarbonyl compounds and their phosphazines: synthesis of pyrazoles and pyridazines

3-(Trifluoromethyl)-substituted (F) 2-vinyl-2-diazocarbonyl compounds, having cis-relationship of functional groups (AlkO₂C, CN₂), do not undergo 1,5-electrocyclization, but readily take part in the tandem Staudinger-diaza-Wittig reactions to produce trifluoromethyl-substituted pyridazines, whereas their non-fluorinated analogs (H), with trans-configuration, easily cyclize to pyrazoles, but remain intact under Staudinger-diaza-Wittig reaction conditions. The difference in the reactivity of H- and F-vinyldiazoketones, vinyldiazoacetates, and derived phosphazines is apparently caused by the different stereochemical arrangements of the AlkO₂C and CN₂ groups.     

The interaction between polymerization initiators and inhibitors in solutions—II. The reaction between benzoyl peroxide and p-benzoquinone in concentrated solutions; Some observations on the induced decomposition of the peroxide

The reaction between benzoyl peroxide and p-benzoquinone in concentrated solutions in a wide variety of solvents has been investigated by isolation and identification of the reaction products. Despite the high efficiency of p-benzoquinone as a trap for benzoyloxy radicals, partial decarboxylation to phenyl radicals usually occurs. Complete suppression of decarboxylation is achieved only when p-benzoquinone is present at such a high concentration that it is effectively the solvent for the reaction.The benzoyloxy- and phenyl semiquinones show marked differences in reactivity, the former tend to combine to form dibenzoyloxy dibenzoquinone while disproportionation is favoured by the latter to form quinhydrone of monophenylbenzoquinone.At lower quinone ratio, the peroxide undergoes induced decomposition by phenyl radicals both in “reactive” and “unreactive” solvents. The induced decomposition involves the formation of radical intermediates which undergo disproportionation, but not intramolecular rearrangement, to form p-phenylbenzoyloxy radicals. The latter can be captured, before undergoing decarboxylation, by the benzoyloxysemiquinones formed in the reaction.A correlation between the electron donating property of a radical and its capability to induce the decomposition of the peroxide was developed.     

Rhodium complexes of PCNHCP: Oxidative addition of dichloromethane and catalytic hydrosilylation of alkynes affording (E)-alkenylsilanes

New rhodium complexes of PC^NHCP have been synthesized by using the silver transfer reagent, [Ag₃(PC^NHCP)₂Cl]Cl₂ (2). In the reaction between 2 and [Rh(COD)Cl]₂ in dichloromethane, the presumably formed nucleophilic Rh^I(PC^NHCP)Cl intermediate (A), undergoes a C–Cl bond activation of CH₂Cl₂ giving cis,mer-Rh^III(PC^NHCP)(CH₂Cl)Cl₂ (3) as the final product. Attempts to isolate A affords the oxidative degradation product of mer-Rh^III(PC^NHCP)Cl₃ complex (4). In contrast, the rhodium(I) center in Rh(PC^NHCP)(CO)Cl (5) is stabilized by the π-back bonding of CO ligand; a robust complex is, therefore, obtained. The solid-state structures of 2 and 3 were determined by X-ray diffraction. Complexes 3–5 are catalyst precursors for efficient, chemoselective hydrosilylation of alkynes. For the reaction between phenylacetylene and dimethylphenylsilane, a rapid hydrosilylation occurs, producing isomers of alkenylsilanes; then a slow isomerization pathway converts (Z)-alkenylsilane to its (E)-isomer. For 3, under catalytic condition, a facile reductive elimination of dichloromethane giving A is anticipated. The similarity in reactivity and selectivity between 3, 4 and 5 suggests the involvement of A as the active species in a common catalytic cycle.     

Solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes under high-speed vibration milling

The solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes (RCHO) 2a-e under high-speed vibration milling (HSVM) conditions have been investigated. Fulleropyrrolidines 4a-e (C₆₀(CH₂N(CH₃)CHR), R=H (4a), C₆H₅ (4b), p-NO₂-C₆H₄ (4c), p-CH₃O-C₆H₄ (4d), p-(CH₃)₂N-C₆H₄ (4e)) were obtained in moderate yields from reactions of C₆₀ with aldehydes 2a-e and N-methylglycine (Prato reaction). In all these solvent-free reactions, 4a was found to be formed besides 4b-e, indicating that fullerenes can react with N-substituted glycines in the absence of aldehyde to give fulleropyrrolidines. For this novel reaction, a possible reaction mechanism involving an electron transfer process has been proposed. Intrigued by this observation, the dependence of the yield on the reagent ratio for the reaction of C₆₀ with paraformaldehyde and/or N-methylglycine was examined to search the optimal conditions. The reaction of C₇₀ with paraformaldehyde and/or N-methylglycine under HSVM conditions was also studied and was found to give the positional isomers of [70]fulleropyrrolidines.     

A green,simple, catalyst-free,and efficient method for electro-organic synthesis of new benzofuran derivatives

In this work, the electrochemical oxidation of catechols 1a and 1b was studied in the presence of pyrazolidine-3,5-dione (3a), as a nucleophile, in a mixture of ethanol and a phosphate buffer solution (0.1 M, pH 7), as a green medium, using the cyclic voltammetry and controlled-potential coulometry techniques. The results obtained indicated that the oxidized forms of these catechols (2a and 2b) participated in the Michael addition reactions with pyrazolidine-3,5-dione (3a), and converted, via an ECEC mechanism, to their corresponding benzofurans (7a and 7b). In this work, some new benzofuran derivatives were synthesized with good yields and high purities using a facile, one-pot, and environmentally friendly electrochemical method in the absence of any chemical catalyst, toxic solvent, and hard conditions.     

A new finding in selective Baeyer-Villiger oxidation of α-fluorinated ketones; a new and practical route for the synthesis of α-fluorinated esters

α-Fluorinated esters were effectively prepared by the Baeyer-Villiger oxidation of α-fluorinated ketones with m-chloroperbenzoic acid (m-CPBA) under mild conditions. The yield of the esters was influenced by the choice of solvent, base, and substituent on the aryl group of the ketones. 4-Methoxyphenyl substituted fluoroketones were oxidized almost quantitatively with m-CPBA within 10 min to 12 h at room temperature using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a cosolvent with CH₂Cl₂ (1:1, v/v) and aqueous buffer (KH₂PO₄-NaOH, pH 7.6) as an additive base. The oxidation reaction rates of α-fluorinated ketones were higher than those of the corresponding non-fluorinated ketones. The fluorine atom at α-position of fluoromethyl aryl ketones enhanced the reactivity in the Baeyer-Villiger oxidation.     

A theoretical investigation into chiral phosphoric acid-catalyzed asymmetric Friedel-Crafts reactions of nitroolefins and 4,7-dihydroindoles: reactivity and enantioselectivity

This article mainly focused on high level Density Functional Theory (DFT) studies on the chiral phosphoric acid-catalyzed Friedel-Crafts reactions between 4,7-dihydroindoles and nitroolefins. Firstly, the reactivities of 4,7-dihydroindole and indole in the chiral phosphoric acid-catalyzed Friedel-Crafts reactions with nitroolefin have been compared. The higher reactivity of 4,7-dihydroindole could be attributed to its higher HOMO energy as well as its more suitable trajectory to attack the nitroolefin in the transition state. Secondly, the origin of the enantioselectivity of the chiral phosphoric acid-catalyzed Friedel-Crafts reaction of 4,7-dihydroindole with nitroolefin has been studied using complete models on PBE1PBE/[6-311+G(d,p), 6-31G(d,p)] level. When (S)-1b was used as the catalyst, the enantioselectivity of the reaction is entirely controlled by the steric effect between the catalyst and the substrate. Whereas for catalyst (S)-1c the enantioselectivity is determined by the solvent effect.     

Further studies of tetrakis(N,N′-dialkylbenzamidinato)diruthenium(III) chloro and alkynyl compounds: molecular engineering of metallayne monomers

Three diruthenium(III) compounds Ru₂(L)₄Cl₂, where L is mMeODMBA (N,N′-dimethyl-3-methoxybenzamidinate, 1a), DiMeODMBA (N,N′-dimethyl-3,5-dimethoxy benzamidinate, 1b), or DEBA (N,N′-diethylbenzamidinate, 1c), were prepared from the reactions between Ru₂(OAc)₄Cl and respective HL under reflux conditions. Metathesis reactions between 1 and LiC₂Y resulted in bis-alkynyl derivatives Ru₂(L)₄(C₂Y)₂ [Y=Ph (2), SiMe₃ (3), SiⁱPr₃ (4) and C₂SiMe₃ (5)]. The parent compounds 1 are paramagnetic (S=1), while bis-alkynyl derivatives 2-5 are diamagnetic and display well-solved ¹H- and ¹³C-NMR spectra. Molecular structures of compounds 1b, 1c, 2c, 3c and 4b were established through single crystal X-ray diffraction studies, which revealed RuRu bond lengths of ca. 2.32 Å for parent compounds 1 and 2.45 Å for bis-alkynyl derivatives. Cyclic voltammograms of all compounds feature three one-electron couples: an oxidation and two reductions, while the reversibility of observed couples depends on the nature of axial ligands.     

The structure and synthesis of alliodorin

A new phenolic terpene aldehyde, alliodorin (1a), has been isolated from Cordia alliodora and shown to be a derivative of geranylhydroquinone. Alliodorin diacetate was synthesized by geranylation of hydroquinone followed by acetylation and finally by oxidation with selenium dioxide, thus confirming the assigned structure. Several other compounds from the oxidation reaction were isolated and characterized.     

Substitution reactions in ionic liquids. A kinetic study

The rate of the substitution reaction of (R)-3-chloro-3,7-dimethyloctane (1) with either methanol or benzyl alcohol in mixtures containing the ionic liquid [Bmim][N(CF₃SO₂)₂] was monitored using ³⁵Cl NMR spectroscopy. The enantiomeric excess of the product, (S)-3-methoxy-3,7-dimethyloctane (2a), was analyzed using chiral gas chromatography. This product showed a decreasing enantiomeric excess with increasing concentration of ionic liquid. The rate of reaction of substrate 1 in each case varied with the concentration of the ionic liquid. Polarity measurements of the solvent mixtures were undertaken by standard methods, which are compared both to each other and to the observed rates. Solvent reorganization and selective solvation are also each proposed as contributing to the difference in the observed rates of reaction.     

Synthesis,crystal structures and spectra of Hg(II)-1,2-bis(diphenylphosphino)ethane monoxide complexes: Monomer and polymer formation

The reaction of mercury(II) halides with 1,2-bis(diphenylphosphino)ethane monoxide (dppeO) in 1:1 molar ratio yielded P,O-coordinated polymers having the empirical formula [HgX₂(dppeO)]_n [X = Cl (1), Br (2), I (3)]. In contrast, the reaction between the same reactants in a 1:2 molar ratio yielded the P, P-coordinated monomeric complexes, HgX₂(dppeO)₂[X = Cl (4), Br (5), I (6)]. The structures of 2, 3, 4 and 5 have been characterized crystallographically. The results indicate that the geometry around the mercury atom in each of these molecules is tetrahedral with considerable distortion. The ³¹P NMR spectra of the 1:1 complexes indicate the dissociation of the Hg–O bond in solution.     

Conformational effects in compounds with 6-membered rings—X : Synthesis of cis- and trans-3,5-di-t-butylthian and sulphonium salt formation from thians

Convenient stereospecific syntheses of cis- and trans-3,5-di-t-butylthian (1 and 2) have been developed. The reaction between anancomeric thians with unhindered S atoms and methyl iodide has been investigated and a range of kinetic (from 6.5 up to 11:1) and thermodynamic (from 1.25 up to 2.8:1) stereoselectivities, with equatorial $\text{S}\text{+}$-Me always favoured, have been observed. It is concluded that the observed stereoselectivities are best explained by steric hindrance at the axial site on sulphur and that twist conformers do not contribute significantly to the reactivity of most thians in such reactions. The contrast between relative kinetic and thermodynamic stereoselectivities shown in the reaction between methyl iodide and either N-methylpiperidines or thians is explained by different directions of approach to these 6-membered rings during axial attack.Acid anhydrides have been isolated from the oxidation of β-diketones by ozone and by chromic acid.     

Copper-sulfide cluster assembled architecture via in situ reaction

A new copper-thiolate cluster assembled framework [Cu₂(μ₄-SCH₃)Cl]_n (1), has been solvothermally synthesized through in situ reaction viz., in situ ligand generation and metal reduction. Compound 1 represents the first 3D framework based on Atlas-sphere functionalized by single μ₂-Cl⁻ groups. DOS calculation reveals the interaction of electronic structures. It is found that the HOMO is mainly distributed on Cl, Cu and S bonding orbitals, while the LUMO is dominated by Cu-Cl antibonding orbitals.     

Metal(salen)-catalyzed oxidation of limonene in supercritical CO2

Summary The Mn(Salen)Cl and Ni(Salen)-catalyzed oxidation of limonene has been carried out. The catalytic cycle involved PhIO via a rebound mechanism. In all cases the use of organic solvents resulted in reasonable selectivities of oxidized products. The use of supercritical carbon dioxide (SCCO₂) led at least to comparable results in terms of conversions, but showed different selectivities. In ordinary solvents epoxidation appears to predominate over allylic oxidation. This tendency, in SCCO₂, appears only after 4 h of reaction. Shorter reaction times (2 h) appear to lead to opposite selectivity. These results showed the advantages of using SCCO₂ as solvent in these reactions. SCCO₂ is much more compatible with green technology than are organic solvents.     

Six-membered cyclometallated derivatives of platinum(II) derived from 2-benzylpyridines. Crystal and molecular structure of [Pt(L)(Ph3P)Cl] (HL = 2-(1-methylbenzyl)pyridine)

The reaction of K₂[PtCl₄] with 2-(1-methylbenzyl)pyridine, HL, and 2-benzylpyridine, HL', affords the cyclometallated species [{Pt(L)Cl}₂] (1) and [{Pt(L')Cl}₂] (2), respectively. The chloride bridge in complex 1 can be split by neutral or anionic species to give the monomeric, [Pt(L)(Ph₃P)Cl], as two isomers, trans-P-Pt-C (3) and trans-P-Pt-N, (4), [Pt(L)(py)Cl] (5), [Pt(L)(CO)Cl] (6), [Pt(L)(CNCH₂SO₂C₆H₄CH₃-4)Cl] (7), [Pt(L)(acac)] (Hacac = 2,4-pentanedione) (8), [Pt(L)(dppm)][BF₄] (dppm = bis(diphenyl-phosphino)methane) (9), [Pt(L)(dppe)][BF₄] (dppe = bis(diphenylphosphino)ethane) (10) and [Pt(L)(dipy)][BF₄](dipy = 2,2'-dipyridine) (11). Similarly, compound 2, by reaction with Ph₃P, affords [Pt(L')(Ph₃P)Cl], as two isomers, trans-P-Pt-C (12) and trans-P-Pt-N (13). Reaction of compounds 1 or 4 with AgBF₄ in acetonitrile affords [Pt(L)(CH₃CN)₂IBF₄] (14) or [Pt(L)(Ph₃P)-(CH₃CN)][BF₄] (15). From these, [Pt(L)(Ph₃P)₂][BF₄] (16), [Pt(L)(Ph₃P)(CO)][BF₄] (17) and [Pt(L)(Ph₃P)(py)][BF₄] (18), can be obtained by displacement of the coordinated acetonitrile. The new complexes were characterized by IR, ¹H and ³¹P NMR and FAB-MS spectroscopic techniques. The NMR spectra at room temperature of most of the species derived from HL give evidence for the presence in solution of two diastereomers a and b. The structure of one diastereomer of complex 4 has been solved by single crystal X-ray diffraction, 4b. The platinum atom is in an almost square planar geometry with a P-Pt-N trans arrangement: Pt-N = 2.095(3), Pt-C = 1.998(4), Pt-P = 2.226(1) and Pt-Cl = 2.400(1) Å. The six-membered cyclometallated ring is in a boat conformation, with the CH₃ group in an equatorial position, i.e pointing away from the metal. Attempts to obtain [{Pt(L″)Cl}₂] (HL″ = 2-(dimethylbenzyl)pyridine), afforded an insoluble product heavily contaminated by platinum metal; treatment of this crude material with Ph₃P gave [Pt(L″)(Ph₃P)Cl] (19).