Competitive Gold‐Promoted Meyer–Schuster and oxy‐Cope Rearrangements of 3‐Acyloxy‐1,5‐enynes: Selective Catalysis for the Synthesis of (+)‐(S)‐γ‐Ionone and (−)‐(2S,6 R)‐cis‐γ‐Irone

We report a simple, highly stereoselective synthesis of (+)‐(S)‐γ‐ionone and (‐)‐(2S,6R)‐cis‐γ‐irone, two characteristic and precious odorants; the latter compound is a constituent of the essential oil obtained from iris rhizomes. Of general interest in this approach are the photoisomerization of an endo trisubstituted cyclohexene double bond to an exo vinyl group and the installation of the enone side chain through a [(NHC)Au^I]‐catalyzed Meyer–Schuster‐like rearrangement. This required a careful investigation of the mechanism of the gold‐catalyzed reaction and a judicious selection of reaction conditions. In fact, it was found that the Meyer–Schuster reaction may compete with the oxy‐Cope rearrangement. Gold‐based catalytic systems can promote either reaction selectively. In the present system, the mononuclear gold complex [Au(IPr)Cl], in combination with the silver salt AgSbF₆ in 100:1 butan‐2‐one/H₂O, proved to efficiently promote the Meyer–Schuster rearrangement of propargylic benzoates, whereas the digold catalyst [{Au(IPr)}₂(μ‐OH)][BF₄] in anhydrous dichloromethane selectively promoted the oxy‐Cope rearrangement of propargylic alcohols.     

Structure and coordination properties of facilitated olefin transport membranes consisting of crosslinked poly(vinyl alcohol) and silver hexafluoroantimonate

The high selectivity of solid‐state crosslinked poly(vinyl alcohol) (CPVA) membranes containing silver hexafluoroantimonate (AgSbF₆), with respect to olefin/paraffin mixtures, was previously reported. The structure and coordination properties of CPVA/AgSbF₆ complexes were investigated in this study with wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), and theoretical ab initio calculations, and they were compared with those of poly(vinyl alcohol) (PVA)/AgSbF₆ complexes. Contrary to expectations, the measurements of the intersegmental d‐spacings and glass‐transition temperatures indicated that the chain mobility in the PVA/AgSbF₆ membranes was lower than that in the CPVA/AgSbF₆ membranes. The different extents of transient crosslinking in the two systems were attributed mostly to their different coordination structures; silver ions in PVA/AgSbF₆ were coordinated with hydroxyl oxygens located near the polymer main chains, whereas those in CPVA/AgSbF₆ were coordinated with aldehyde oxygens located far from the main chains. According to WAXS spectra, AgSbF₆ was completely dissolved in both PVA and CPVA, and this disrupted the crystallinity of the polymers. However, our DSC study showed that the silver ions dissolved in both polymer matrices recrystallized into silver oxide at elevated temperatures. The binding energy of Ag3d_5/2, as determined from XPS spectra, shifted to lower values with the addition of increasing amounts of the polymer matrix, indicating the increasing coordination of silver ions with polymer chains. The presence of various oxygen species with and without coordination to silver ions was confirmed from O1s XPS spectra of CPVA membranes containing silver ions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 621–628, 2004     

A General Diversified Synthesis of Carbazoles and the First Synthesis of Karapinchamine A

[IPrAuCl]/AgSbF₆‐catalyzed cyclization of the readily available 4‐benzoxyl‐1‐(indol‐2‐yl)‐2‐alkynols occurred smoothly in 1,2‐dichloroethane (DCE) in the presence of 4 Å MS to form a series of differently polysubstituted 2‐oxygenated carbazole derivatives efficiently. Based on mechanistic study, a possible mechanism involving 1,3‐migration of a benzoate group to form the allene, Au⁺‐mediated cyclization–elimination to form a gold–carbene intermediate, and subsequent highly selective 1,2‐migration has been proposed for the formation of carbazoles. Highly selective 1,2‐migration referring to the two substituents R³ and R⁴ (R⁴=H, alkyl, and aryl group) was observed: (1) In the presence of both H and alkyl groups, 1,2‐hydrogen migration is exclusive; (2) in the presence of a methyl group (R³), propyl, isopropyl, 4‐methylphenyl, and 4‐chlorophenyl groups (R⁴) migrate exclusively. Finally, the first total synthesis of the recently isolated naturally occurring carbazole alkaloid karapinchamine A in 5.2 g scale has been realized in 6 steps from commercially available chemicals without need for any protection–deprotection.     

Synthesis and Study of Cationic,Two‐Coordinate Triphenylphosphine– Gold–π Complexes

Cationic, two‐coordinate triphenylphosphine–gold(I)–π complexes of the form [(PPh₃)Au(π ligand)]⁺ SbF₆^? (π ligand=4‐methylstyrene, 1? SbF₆), 2‐methyl‐2‐butene ( 3? SbF₆), 3‐hexyne ( 6? SbF₆), 1,3‐cyclohexadiene ( 7? SbF₆), 3‐methyl‐1,2‐butadiene ( 8? SbF₆), and 1,7‐diphenyl‐3,4‐heptadiene ( 10? SbF₆) were generated in situ from reaction of [(PPh₃)AuCl], AgSbF₆, and π ligand at ?78 °C and were characterized by low‐temperature, multinuclear NMR spectroscopy without isolation. The π ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (ΔG^≠≈9 kcal mol^?1 in the case of 6? SbF₆) and competitive displacement by weak σ donors, such as trifluoromethane sulfonate. Triphenylphosphine–gold(I)–π complexes were thermally unstable and decomposed above ?20 °C to form the bis(triphenylphosphine) gold cation [(PPh₃)₂Au]⁺SbF₆^? ( 2? SbF₆).     

1,1′‐[(Ethane‐1,2‐diyldioxy)di‐o‐phenylene]bis(indoline‐2,3‐dione) (L) and a novel [Ag2L2]2+ metallocycle based on coordination‐driven Ag—O and Ag—π bonds

1,1′‐[(Ethane‐1,2‐diyldioxy)di‐o‐phenylene]bis(indoline‐2,3‐dione), C₃₂H₂₄N₂O₆, L or (I), adopts a trans conformation with the two terminal indoline‐2,3‐dione groups located on opposite sides of the central ether bridge, as required by a centre of inversion located at the mid‐point of the ethane C—C bond. However, in the discrete binuclear Ag^I metallocycle complex salt bis{μ‐1,1′‐[(ethane‐1,2‐diyldioxy)di‐o‐phenylene]bis(indoline‐2,3‐dione)}disilver(I) bis(hexafluoridoantimonate), [Ag₂(C₃₂H₂₄N₂O₆)₂][SbF₆]₂, (II), synthesized by combination of L with AgSbF₆, L adopts a gauche conformation to bind Ag^Ivia the two indolinedione O atoms and two C atoms from the phenoxy ring. One dione O atom from the opposite side of the ether bridge completes the irregular coordination environment of each Ag^I atom. The complex is on a centre of inversion located between the Ag^I atoms. In the solid state, these binuclear [Ag₂L₂]²⁺ metallocycles stack together via intermolecular π–π interactions to generate a one‐dimensional chain motif, with the [SbF₆]⁻ counter‐ions, which are disordered, located between the chains.     

Isomerization,Ring Expansion,and Ring Contraction of 1,3‐Diphosphete Complexes

Reactions between the 1,3‐diphosphete complex [Cp′′′Co(η⁴‐P₂C₂tBu₂)] ( 1 ) and Ag[Al{OC(CF₃)₃}₄] (Ag[pftb]) were carried out under different conditions. In CH₂Cl₂, the unprecedented 1,2‐diphosphete isomerization product [Ag₂{Cp′′′Co(μ,η⁴:η¹:η¹‐1,2‐P₂C₂tBu₂)}₂{Cp′′′Co(μ,η⁴:η¹‐1,2‐P₂C₂tBu₂)}₂]⋅2[pftb] ( 2 ) could be isolated. In diffusion experiments of 1 in n‐hexane with Ag[pftb] in CH₂Cl₂, the triphosphacobaltocenium complex [Cp′′′Co(η⁵‐P₃C₂tBu₂)][pftb] ( 4 ) and the phosphirenylium complex [Cp′′′Co(η³‐PC₂tBu₂)][pftb] ( 5 ) were obtained, showing a ring expansion and a ring contraction, respectively, under mild conditions. Moreover, addition of pyridine to the Ag complex 2 led to the new 1,2‐diphosphete complex [Cp′′′Co(η⁴‐1,2‐P₂C₂tBu₂)] ( 3 ). Compound 3 is also formed by thermolysis of 1 , making it a promising method for this type of isomerization. 1,2‐Diphosphete complexes like 3 are thermodynamically more stable but also synthetically more elusive than their 1,3‐isomer counterparts.     

N‐Heterocyclic Carbene–Phosphinidene Complexes of the Coinage Metals

Coinage metal complexes of the N‐heterocyclic carbene–phosphinidene adduct IPr ? PPh (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me₂S)AuCl], which afforded the monometallic complexes [(IPr ? PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr ? PPh)(MCl)₂] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr ? PPh)(CuOTf)₂] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr ? PPh)(MCl)₂] (M=Cu, Au) with Na(BAr^F) or AgSbF₆ afforded the tetranuclear complexes [(IPr ? PPh)₂M₄Cl₂]X₂ (X=BAr^F or SbF₆), which contain unusual eight‐membered M₄Cl₂P₂ rings with short cuprophilic or aurophilic contacts along the chlorine‐bridged M???M axes. Complete chloride abstraction from [(IPr ? PPh)(AuCl)₂] was achieved with two equivalents of AgSbF₆ in the presence of tetrahydrothiophene (THT) to form [(IPr ? PPh){Au(THT)}₂][SbF₆]₂. The cationic tetra‐ and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions.     

Luminescent Di‐ and Polynuclear Organometallic Gold(I)–Metal (Au2, {Au2Ag}n and {Au2Cu}n) Compounds Containing Bidentate Phosphanes as Active Antimicrobial Agents

The reaction of new dinuclear gold(I) organometallic complexes containing mesityl ligands and bridging bidentate phosphanes [Au₂(mes)₂(μ‐LL)] (LL=dppe: 1,2‐bis(diphenylphosphano)ethane 1 a , and water‐soluble dppy: 1,2‐bis(di‐3‐pyridylphosphano)ethane 1 b ) with Ag⁺ and Cu⁺ lead to the formation of a family of heterometallic clusters with mesityl bridging ligands of the general formula [Au₂M(μ‐mes)₂(μ‐LL)][A] (M=Ag, A=ClO₄^?, LL=dppe 2 a , dppy 2 b ; M=Ag, A=SO₃CF₃^?, LL=dppe 3 a , dppy 3 b ; M=Cu, A=PF₆^?, LL=dppe 4 a , dppy 4 b ). The new compounds were characterized by different spectroscopic techniques and mass spectrometry The crystal structures of [Au₂(mes)₂(μ‐dppy)] ( 1 b ) and [Au₂Ag(μ‐mes)₂(μ‐dppe)][SO₃CF₃] ( 3 a ) were determined by a single‐crystal X‐ray diffraction study. 3 a in solid state is not a cyclic trinuclear Au₂Ag derivative but it gives an open polymeric structure instead, with the {Au₂(μ‐dppe)} fragments “linked” by {Ag(μ‐mes)₂} units. The very short distances of 2.7559(6) Å (Au? Ag) and 2.9229(8) Å (Au? Au) are indicative of gold–silver (metallophilic) and aurophilic interactions. A systematic study of their luminescence properties revealed that all compounds are brightly luminescent in solid state, at room temperature (RT) and at 77 K, or in frozen DMSO solutions with lifetimes in the microsecond range and probably due to the self‐aggregation of [Au₂M(μ‐mes)₂(μ‐LL)]⁺ units (M=Ag or Cu; LL=dppe or dppy) into an extended chain structure, through Au? Au and/or Au? M metallophilic interactions, as that observed for 3 a . In solid state the heterometallic Au₂M complexes with dppe ( 2 a – 4 a ) show a shift of emission maxima (from ca. 430 to the range of 520‐540 nm) as compared to the parent dinuclear organometallic product 1 a while the complexes with dppy ( 2 b–4 b ) display a more moderate shift (505 for 1 b to a max of 563 nm for 4 b ). More importantly, compound [Au₂Ag(μ‐mes)₂(μ‐dppy)]ClO₄ ( 2 b ) resulted luminescent in diluted DMSO solution at room temperature. Previously reported compound [Au₂Cl₂(μ‐LL)] (LL dppy 5 b ) was also studied for comparative purposes. The antimicrobial activity of 1–5 and Ag[A] (A=ClO₄^?, SO₃CF₃^?) against Gram‐positive and Gram‐negative bacteria and yeast was evaluated. Most tested compounds displayed moderate to high antibacterial activity while heteronuclear Au₂M derivatives with dppe ( 2 a – 4 a ) were the more active (minimum inhibitory concentration 10 to 1 μg mL^?1). Compounds containing silver were ten times more active to Gram‐negative bacteria than the parent dinuclear compound 1 a or silver salts. Au₂Ag compounds with dppy ( 2 b , 3 b ) were also potent against fungi.     

Rhodium(III)‐Catalyzed Enantioselective Coupling of Indoles and 7‐Azabenzonorbornadienes by C−H Activation/Desymmetrization

Chiral rhodium(III) cyclopentadienyl catalysts (Cp^XRh^III) play significant roles in asymmetric arene C?H activation. Rh/Ir‐catalyzed couplings of arenes and strained rings have been well‐studied, but they have been limited to racemic systems. Reported in this work is the Cp^xRh^III/AgSbF₆‐catalyzed enantioselective desymmetrizative C?C coupling of N‐pyrimidylindoles and 7‐azabenzonorbornadienes with high efficiency and enantioselectivity. The role of AgSbF₆ has been established by mechanistic studies. AgSbF₆ enhances the catalytic activity by suppressing the C3?H activation of the indoles, activation which would otherwise lead to catalytically inactive species.     

Controllable Coordination Self‐Assembly Based on Flexible Tripodal Ligands: From Finite Metallocages to Infinite Polycatenanes Step by Step

This article describes the developments in coordination self‐assembly based on flexible tripodal ligands with different metal species. Various finite metallocages such as M₃L₂, M₆L₈, M₆L₄, M₄L₄ and different catenanes based on discrete metallocages constructed from flexible tripodal ligands with suitable metal species are presented here. Many M₃L₂ metallocages based on ligands L¹–L¹² and different two‐coordinated metal species have been prepared, in which various Ag(I) salts and other metal species that have been protected by suitable groups, such as Zn(OAc)₂, ZnBr₂, and PdBr₂, have been used as effective acceptors. All of the M₆L₈‐type metallocages are constructed from ligands L² or L¹²–L²⁰ and different four‐coordinated metal species, such as various palladium(II) salts or NiCl₂, and have similar topological structures. Only a few discrete M₆L₄‐type metallocages, based on ligands L²¹–L²⁴, have been reported, using different strategies such as protecting groups and steric hindrance. All of the M₄L₄‐type cages have similar topological structures and are constructed from ligands L²⁵–L²⁹ with multiple donor sites. More intriguing interlocking ensembles constructed from discrete metallocages are also described here in detail, namely, three [2]catenanes based on ligands L³⁰–L³² and four polycatenanes based on ligands L³³–L³⁴.     

Ring‐opening polymerization of cyclic ethers initiated by benzazaphosphole‐W(CO)5/silver hexafluoroantimonate

Attempts to prepare mixed M(0)/Ag⁺ complexes with µ‐bridging P ligands by reaction of benzazaphosphole M(CO)₅ complexes 1a–e (M?W, Mo, Cr) with AgSbF₆ in THF lead to rapid ring‐opening polymerization of this ether at room temperature and, as shown for 1a /AgSbF₆, even at low temperature. Oxetane and epoxides (styrene oxide and cyclohexene oxide) polymerize even more vigorously in the presence of this initiator and require dilution with toluene to control the strongly exothermic reaction. Related P(III)W(CO)₅/AgSbF₆ systems with Ph₃P, (EtO)₃P or 2,4,6‐triphenyl‐phosphinine ligands also initiate the THF polymerization, but less efficiently. Efforts to isolate the initiator complex in other solvents failed because of its high sensitivity to nucleophiles and provided 2a ,characterized by crystal structure analysis as the addition product of methanol at 1a , although 1a itself is stable towards MeOH. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 664–670     

Platinum and Palladium Complexes Bearing New (1R,2R)‐(–)‐1,2‐Diaminocyclohexane (DACH)‐Based Nitrogen Ligands: Evaluation of the Complexes Against L1210 Leukemia

The reaction of (1R,2R)‐(–)‐1,2‐diaminocyclohexane ( 1 ) [DACH] with the aldehyde (1R)‐(–)‐myrtenal ( 2 ) in MeOH afforded the bidentate diimine ligand, (1R,2R)‐(–)‐N¹,N²‐bis{(1R)‐(–)myrtenylidene}‐1,2‐diaminocyclohexane ( 3 ) in a high yield. Reduction of 3 using LiAlH₄ led to the formation of the desired ligand ( 4 ) (1R,2R)‐(–)‐N¹,N²‐bis{(1R)‐(–)myrtenyl}‐1,2‐diaminocyclohexane. Treatment of compound 4 with K₂PtCl₄ or K₂PdCl₄ yielded the corresponding platinum(II) and palladium(II) complexes, Pt‐5 and Pd‐6 , respectively. The reaction of compound 3 with K₂PtCl₄ gave the diimine complex Pt‐7 . The cytotoxic activity of the complexes Pt‐5 , Pd‐6 and Pt‐7 was tested and compared to the approved drugs, cisplatin ( Cis ‐Pt ) and oxaliplatin ( Ox‐Pt ). The complexes ( Pt‐5 , Pd‐6 and Pt‐7 ) inhibit L1210 cell line proliferation with an IC₅₀ of 0.6, 4.2, and 0.7 μL, respectively as evidenced by measuring thymidine incorporation.     

Silver-silver(I) system in superacid mixtures HF+SbF5

An electrochemical study of silver in superacid medium HF+SbF₅ shows that Ag is not oxidized and that the couple Ag/Ag(I) may be used as a reference electrode in mixtures of HF and SbF₅ containing 30% of SbF₅ (by weight). From potentiometric measurements with a silver electrode, it is shown that AgSbF₆ is slightly soluble and the solubility product is determined (log(K_s/mol²l^?2)=1.1). Evidence for the strong acidity of SbF₅ is demonstrated and it is shown that there are no polymers (such as Sb₂F₁₁^?) in the concentration range 0–3 M of SbF₅.     

Diversification of ortho‐Fused Cycloocta‐2,5‐dien‐1‐one Cores and Eight‐ to Six‐Ring Conversion by σ Bond C−C Cleavage

Sequential treatment of 2‐C₆H₄Br(CHO) with LiC≡CR¹ (R¹=SiMe₃, tBu), nBuLi, CuBr?SMe₂ and HC≡CCHClR² [R²=Ph, 4‐CF₃Ph, 3‐CNPh, 4‐(MeO₂C)Ph] at ?50 °C leads to formation of an intermediate carbanion (Z)‐1,2‐C₆H₄{C_A(=O)C≡C_BR¹}{CH=CH(CH^?)R²} ( 4 ). Low temperatures (?50 °C) favour attack at C_B leading to kinetic formation of 6,8‐bicycles containing non‐classical C‐carbanion enolates ( 5 ). Higher temperatures (?10 °C to ambient) and electron‐deficient R² favour retro σ‐bond C?C cleavage regenerating 4 , which subsequently closes on C_A providing 6,6‐bicyclic alkoxides ( 6 ). Computational modelling (CBS‐QB3) indicated that both pathways are viable and of similar energies. Reaction of 6 with H⁺ gave 1,2‐dihydronaphthalen‐1‐ols, or under dehydrating conditions, 2‐aryl‐1‐alkynylnaphthlenes. Enolates 5 react in situ with: H₂O, D₂O, I₂, allylbromide, S₂Me₂, CO₂ and lead to the expected C ‐E derivatives (E=H, D, I, allyl, SMe, CO₂H) in 49–64 % yield directly from intermediate 5 . The parents (E=H; R¹=SiMe₃, tBu; R²=Ph) are versatile starting materials for NaBH₄ and Grignard C=O additions, desilylation (when R¹=SiMe) and oxime formation. The latter allows formation of 6,9‐bicyclics via Beckmann rearrangement. The 6,8‐ring iodides are suitable Suzuki precursors for Pd‐catalysed C?C coupling (81–87 %), whereas the carboxylic acids readily form amides under T3P® conditions (71–95 %).     

Silver(I) Complexes with a Bulky Anthracene‐Based Dicarboxylic Ligand: Syntheses,Crystal Structures,and Luminescent Properties

To explore the influence of anthracene skeleton with a larger conjugated π‐system on the structures and properties of its complexes, two Ag^I–carboxylate complexes based on anthracene‐9,10‐dicarboxylate (L) were synthesized and characterized: [{[Ag(L)][Ag(dmpy)₂]}_∞] ( 1 ) and [{[Ag₂(L)(bipy)₂]}_∞] ( 2 ) (dmpy = 2,6‐dimethylpyridine and bipy = 4,4′‐bipyridine). Complex 1 has an interesting framework consisting of anionic chains {[Ag(L)]^–}_∞ and the mononuclear cationic units [Ag(dmpy)₂]⁺, which is further assembled to form networks along the different crystallographic directions by the intermolecular C–H ··· Ag hydrogen‐bonding interactions. Complex 2 takes a ladder‐like chain structure by incorporating 4,4′‐bipyridine (bipy) as a bridging co‐ligand, which is further interlinked to generate a planar network through interchain Ag–Ag bonding contacts. The steric bulk of anthracene ring in L may play an important role in the formation of 1 and 2 . Moreover, the luminescent properties of the 1 and 2 were investigated in detail.     

A two‐dimensional undulating AgI coordination polymer constructed of Ag—C and Ag—O bonds: poly[[[μ3‐(5,6‐η):κO2:κO2‐(±)‐(1S,2S,3R,4R)‐3‐carboxy‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2‐carboxylato]silver(I)] monohydrate]

The title coordination polymer, {[Ag(C₈H₇O₅)]·H₂O}_n, is built from Ag⁺ cations and singly protonated dehydronorcantharidin (SP‐DNC) anions, with a distorted trigonal‐planar geometry at the metal centre. The coordination number of Ag^I is three (with one Ag—π bond and two Ag—O bonds, one from each of three different SP‐DNC ligands), if only formal Ag–ligand bonds are considered, but can be regarded as five if longer weak Ag...O interactions are also included. The two‐dimensional corrugated‐sheet coordination polymer forms a non‐interpenetrating framework with (4.8²) topology. Disordered water molecules are sandwiched between the sheets.     

Hexagonal Double Perovskite Cs2AgCrCl6

The quaternary halide Cs₂AgCrCl₆ was prepared in the form of dark purple crystals by reaction of CsCl, AgCl, and CrCl₃, at 700 °C. It crystallizes in the trigonal Ba₂NiTeO₆‐type structure [space group R3 m, Z = 6, a = 7.2692(4) Å, c = 36.443(2) Å] belonging to the family of perovskite polytypes containing sequences of hexagonal close‐packed layers. Groups of three face‐sharing octahedra, which are occupied in the sequence Ag–Cr–Ag, are connected through corner‐sharing by Cr‐centered octahedra. The UV/Vis/NIR diffuse reflectance spectrum shows absorptions arising from d–d transitions typical of octahedral Cr³⁺ complexes, as confirmed by electronic structure calculations. The compound melts at 506 °C. Magnetic measurements revealed simple paramagnetic behavior consistent with the presence of isolated Cr³⁺ ions.     

Simultaneous determination of three chloroacetic acids,three herbicides,and 12 anions in water by ion chromatography

An ion chromatography method was developed for the simultaneous detection of three soluble herbicides (glyphosate, bentazone and picloram), three chlorine disinfection byproducts (monochloroacetic acid, dichloroacetic acid and trichloroacetic acid) and 12 anions in water (Cl^–, Br^–, SO₄^2–, CO₃^2–, ClO₃^–, ClO₄^–, BrO₃^–, PO₄^3–, NO₂^–, NO₃^–, CH₃COO^– and COO^–). High linearity (r² > 0.996) was observed for all target analytes for each respective concentration range. The limit of detection and limit of quantitation were between 0.21–0.85 and 0.06–25.46 μg/L, respectively. However, the interference effect of Cl^–, NO₃^–, SO₄^2– and CO₃^2– on some target analytes must be considered during the analysis. Sample pre‐treatment by a hydrogen column (H‐column) required to reduce the negative effect of CO₃^2–. Additionally, sample pre‐treatment by a sliver–hydrogen column (Ag–H‐column) is required when Cl^– > 100 mg/L and SO₄^2– < 50 mg/L, and pre‐treatment by both a barium column (Ba‐column) and an H‐column is required when Cl^– > 100 mg/L and SO₄^2– > 50 mg/L. When Cl^– > 100 mg/L, SO₄^2– > 50 mg/L and CO₃^2– > 20 mg/L, the sample pre‐treatment by either an Ag–H–Ba‐column or an Ag–H‐column and Ba‐column is required to minimize interference.     

Further Explorations into the Synthesis of Dehydro‐Hedione®

Dehydrohedione (DHH) 1 may be obtained in 20% overall yield by a Reformatsky reaction with enone methyl ether 3b , followed by acidic workup of the crude reaction mixture. Alternatively, epoxidation (3‐chloroperbenzoic acid, CH₂Cl₂, 84% yield) of the tertiary allyl alcohol derivative 4 affords a 1 : 2 mixture of 8a and 8b . The latter epoxy ester 8b may also be obtained stereoselectively either from 4 (^tBuO₂H, [Mo(CO)₆], 1,2‐dichloroethane, 70°, 62% yield; or ^tBuO₂H, [VO(acac)₂], decane, 20°, 92% yield), or from 5 (AcOMe, LiN(SiMe₃)₂, THF, ?78°, 84–87%). BF₃?Et₂O‐Catalyzed cascade rearrangement and OH elimination of 8a afford selectively DHH 1 in 88% yield. The cis disposition of the side chains of the weakly odoriferous hedione‐like analogues 2b and 2c was maintained by means of either an epoxy or a cyclopropane moiety.     

Vapor-phase Beckmann rearrangement of oxime molecules over H-Faujasite zeolite.

The Beckmann rearrangement (BR) plays an important role in a variety of industries. The mechanism of this reaction rearrangement of oximes with different molecular sizes, specifically, the oximes of formaldehyde (H₂C?NOH), Z‐acetaldehyde (CH₃HC?NOH), E‐acetaldehyde (CH₃HC?NOH) and acetone (CH₃)₂C?NOH, catalyzed by the Faujasite zeolite is investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6‐31G (d,p) basis set. To enhance the energetic properties, single point calculations are undertaken at MP2/6‐311G(d,p). The rearrangement step, using the bare cluster model, is the rate determining step of the entire reaction of these oxime molecules of which the energy barrier is between 50–70 kcal mol^?1. The more accurate embedded cluster model, in which the effect of the zeolitic framework is included, yields as the rate determining step, the formaldehyde oxime reaction rearrangement with an energy barrier of 50.4 kcal mol^?1. With the inclusion of the methyl substitution at the carbon‐end of formaldehyde oxime, the rate determining step of the reaction becomes the 1,2 H‐shift step for Z‐acetaldehyde oxime (30.5 kcal mol^?1) and acetone oxime (31.2 kcal mol^?1), while, in the E‐acetaldehyde oxime, the rate determining step is either the 1,2 H‐shift (26.2 kcal mol^?1) or the rearrangement step (26.6 kcal mol^?1). These results signify the important role that the effect of the zeolite framework plays in lowering the activation energy by stabilizing all of the ionic species in the process. It should, however, be noted that the sizeable turnover of a reaction catalyzed by the Brønsted acid site might be delayed by the quantitatively high desorption energy of the product and readsorption of the reactant at the active center.