Photochemistry of 4‐ and 5‐ phenyl substituted isoxazoles

5‐Phenylisoxazole ( 4 ) and 4‐phenylisoxazole ( 22 ) underwent phototransposition to 5‐phenyloxazole ( 5 ) and 4‐phenyloxazole ( 24 ) respectively. Labeling with deuterium or methyl confirmed that these phototranspositions occurred via the P₄ pathway which involves only interchange of the N2 and C3 ring position. Thus, 4‐deuterio‐5‐phenylisoxazole ( 4‐4d ), 4‐methyl‐5‐phenylisoxazole ( 10 ), and 5‐methyl‐4‐phenylisoxazole ( 23 ) phototransposed to 4‐deuterio‐5‐phenyloxazole ( 5‐4d ), 4‐methyl‐5‐phenyloxazole ( 11 ), and 5‐methyl‐4‐phenyloxazole ( 25 ) respectively. In addition to phototransposition, isoxazoles 4, 10 , and 23 also underwent photo‐ring cleavage to yield benzoylacetonitrile (9), α‐benzoylpropionitrile ( 15 ), and aceto‐α‐phenylacetonitrile ( 26 ) respectively. Irradiation of 5‐phenyl‐3‐(trifluoromethyl)isoxazole ( 16 ) in acetonitrile led to 5‐phenyl‐2‐(trifluoromethyl)oxazole ( 17 ), the P₄ phototransposition product. Irradiation of 16 in methanol led to a substantial decrease in the yield of 17 and to the formation of a mixture of (E) and (Z)‐2‐methoxy‐2‐(trifluoromethyl)‐3‐benzoylaziridines 18a and 18b .     

Abnormal reactions of 2‐methoxy‐4,9‐dimethyl‐1‐nitroacridine with selenous acid and selenium(IV) oxide. Synthesis of 1H‐selenopheno[2,3,4‐k,l]acridine‐1‐one: A new seleno‐containing ring system

Unusual course of the reaction was revealed on the oxidation of functionally substituted acridine containing the activated methyl groups by well‐known oxidants, such as selenous acid and selenium(IV) oxide. Treatment of 2‐methoxy‐4,9‐dimethyl‐1‐nitroacridine ( 5 ) with an excess of H₂SeO₃ in boiling ethanol gave a mixture of the normal reaction products, 2‐methoxy‐4‐methyl‐1‐nitro‐9‐formylacridine ( 11 ) (isolated yield 29%) and 2‐methoxy‐4‐methyl‐1‐nitroacridine‐9‐carboxylic acid ( 12 ) (36%), together with an abnormal product, 3‐methoxy‐5‐methyl‐1H‐selenopheno[2,3,4‐k,l]acridine‐1‐one ( 13 ) (21%), which is the first example of a new seleno‐containing ring system. With the use of SeO₂ the yield of selenolactone 13 was much lower. J. Heterocyclic Chem., 2011.     

Photochemistry of trifluromethyl substituted 1‐methylpyrazoles

Trifluromethyl substitution on the pyrazole ring was found to enhance photoreactivity via the P₄ pathway which involves interchange of the N2‐C3 ring atoms. Thus, 1‐methyl‐3‐(trifluromethyl)pyrazole (1) and 1‐methyl‐5‐(trifluromethyl)pyrazole (3) transposed with a P₄/P₆ or P₄/P₆+P₇ ratio of 2.1:1. 1‐methyl‐4‐(trifluromethyl)pyrazole (2) transposed regiospecifically by the P₄ transposition pathway. Compounds 2 and 3 were also observed to undergo photocleavage to yield enaminonitrile and enaminoisocyanide products.     

Asymmetric Synthesis of Spiropyrazolones by Rhodium‐Catalyzed C(sp2)−H Functionalization/Annulation Reactions

Rhodium‐catalyzed C(sp²)−H functionalization reactions of 4‐aryl‐5‐pyrazolones followed by [3+2] annulation reactions with alkynes provide rapid access to highly enantioenriched five‐membered‐ring 4‐spiro‐5‐pyrazolones. The use of a chiral SCpRh catalyst enabled the synthesis of a large range of spiropyrazolones with all‐carbon quaternary stereogenic centers in up to 99 % yield and 98 % ee from readily available substrates.     

Cocrystals of diastereoisomers of 1,4‐dihydro­pyridine derivatives

A mixture of the RR/SS and RS/SR diastereoisomeric pairs of methyl 4‐(2,4‐dichloro­phen­yl)‐2,7‐dimethyl‐5‐oxo‐1,4,5,6,7,8‐hexa­hydro­quinoline‐3‐carboxyl­ate, C₁₉H₁₉Cl₂NO₃, forms cocrystals in which there is one unique mol­ecule in the asymmetric unit, but the mol­ecule displays disorder in the region of the 7‐position of the quinoline ring system as a result of the random occurrence of the diastereoisomers at the same crystallographic site. A similar arrangement exists in the monohydrate cocrystals that form from a mixture of the RR/SS and RS/SR diastereoisomeric pairs of methyl 4‐(2,4‐dichloro­phen­yl)‐2‐methyl‐7‐phenyl‐5‐oxo‐1,4,5,6,7,8‐hexa­hydro­quinoline‐3‐carboxyl­ate monohydrate, C₂₄H₂₁Cl₂NO₃·H₂O. These compounds belong to a class of 1,4‐dihydro­pyridines whose members have calcium modulatory properties. The 1,4‐dihydro­pyridine rings have the usual shallow boat conformation. In each structure, the 2,4‐dichloro­phenyl ring is oriented such that the 2‐chloro substituent is in a synperi­planar orientation with respect to the 1,4‐dihydro­pyridine ring plane. In each crystal structure, the mol­ecules are linked into chains by N—H⋯O hydrogen‐bonding inter­actions.     

An Expeditious Synthesis of Methyl Jasmonate

We present an efficient three‐step, two‐pot synthesis of methyl jasmonate (trans‐ 1 ) based on Diels–Alder cycloaddition of cyclopent‐2‐enone ( 2 ) and chloroprene (= 2‐chlorobuta‐1,3‐diene; 3d ) in either CHCl₃ or CH₂Cl₂, catalyzed by SnCl₄ (0.2 mol‐equiv.) at 20° (75% yield). Subsequent ozonolysis of a cis/trans 55 : 45 mixture of the cycloadduct 4d in either CH₂Cl₂ or AcOEt at ? 78°, followed by addition of Me₂S and MeOH in the presence of NaHCO₃, afforded, in 64% yield, a cis/trans 40 : 60 mixture of the known aldehyde 5c . The latter was reacted at ? 50° under salt‐free conditions with the propyl Wittig reactant to furnish 1 as a cis/trans 20 : 80 mixture ((E/Z) 3 : 97). Alternatively, a cis/trans 7 : 93 mixture ((E/Z) 4 : 96) was obtained in 88% yield from epimerized 5c (AcOH, H₂O, 40°; 99%) under usual Wittig conditions at ? 20°.     

Direct Conversion of Syngas into Methyl Acetate,Ethanol, and Ethylene by Relay Catalysis via the Intermediate Dimethyl Ether

Selective conversion of syngas (CO/H₂) into C₂₊ oxygenates is a highly attractive but challenging target. Herein, we report the direct conversion of syngas into methyl acetate (MA) by relay catalysis. MA can be formed at a lower temperature (ca. 473 K) using Cu‐Zn‐Al oxide/H‐ZSM‐5 and zeolite mordenite (H‐MOR) catalysts separated by quartz wool (denoted as Cu‐Zn‐Al/H‐ZSM‐5|H‐MOR) and also at higher temperatures (603–643 K) without significant deactivation using spinel‐structured ZnAl₂O₄|H‐MOR. The selectivity of MA and acetic acid (AA) reaches 87 % at a CO conversion of 11 % at 643 K. Dimethyl ether (DME) is the key intermediate and the carbonylation of DME results in MA with high selectivity. We found that the relay catalysis using ZnAl₂O₄|H‐MOR|ZnAl₂O₄ gives ethanol as the major product, while ethylene is formed with a layer‐by‐layer ZnAl₂O₄|H‐MOR|ZnAl₂O₄|H‐MOR combination. Close proximity between ZnAl₂O₄ and H‐MOR increases ethylene selectivity to 65 %.     

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.     

Rhodium‐Catalyzed 1,4‐Addition of Lithium 2‐Furyltriolborates to Unsaturated Ketones and Esters for Enantioselective Synthesis of γ‐Oxo‐Carboxylic Acids By Oxidation of the Furyl Ring with Ozone

Rhodium‐catalyzed 1,4‐addition of lithium 5‐methyl‐2‐furyltriolborate ([ArB(OCH₂)₃CCH₃]Li, Ar=5‐methyl‐2‐furyl) to unsaturated ketones to give β‐furyl ketones was followed by ozonolysis of the furyl ring for enantioselective synthesis of γ‐oxo‐carboxylic acids. [Rh(nbd)₂]BF₄ (nbd=2,5‐norbornadiene) chelated with 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (binap) or 2,3‐bis(diphenylphosphino)butane (chiraphos) gave high yields and high selectivities in a range of 91–99 % ee at 30 °C in a basic dioxane/water solution. The corresponding reaction of unsaturated esters, such as methyl crotonate, had strong resistance under analogous conditions, but the 1,4‐adduct was obtained in 70 % yield and with 94 % ee when more electron‐deficient phenyl crotonate was used as the substrate.     

Cyclization Reactions of Aryl Propargyl Acetates with Tethered Epoxide Induced by Ruthenium Complex

Reactions of the ruthenium complex [Ru]Cl ([Ru]=Cp(PPh₃)₂Ru; Cp=η⁵‐C₅H₅) with several aryl propargyl acetates, each with an ortho ‐substituted chain of various length containing an epoxide on the aromatic ring and with or without methyl substitutents on the epoxide ring, bring about novel cyclizations. The cyclization reactions of HC≡CCH(OAc)(C₆H₄)CH₂(RC₂H₂O) (R=H, 6 a ; R=CH₃, 6 b , where RC₂H₂O is an epoxide ring) in MeOH give the vinylidene complexes 5 a – b , respectively, each with the Cβ integrated into a tetrahydro‐5H ‐benzo[7]annulen‐6‐ol ring. A C−C bond formation takes place between the propargyl acetate and the less substituted carbon of the epoxide ring. Further cyclizations of 5 a – b induced by HBF₄ give the corresponding vinylidene complexes 8 a – b each with a new 8‐oxabicyclo‐[3.2.1]octane ring by removal of a methanol molecule in high yield. For similar aryl propargyl acetates with a shorter epoxide chain, the cyclization gives a mixture of a vinylidene complex with a tetrahydronaphthalen‐1‐ol ring and a carbene complex with a tricyclic indeno‐furan ring. For the cyclization of 18 , with a longer epoxide chain, opening of the epoxide is required to afford the vicinal bromohydrin 22 , then tandem cyclization occurs in one pot. Products are characterized by spectroscopic methods as well as by XRD analysis.     

A Direct Amination of Isoprene by Aniline – Catalyzed by Palladium Complexes

The reaction of isoprene with aniline, catalyzed by Pd (acac)₂–(RO)₃P‐CF₃COOH, (1:4:4) (R = Me, Et, acac = (CH₃CO)₂CH‐) in MeCN solution, results in high (up to 89 mol.%) selectivity of N–(3‐methyl‐2‐buten‐1‐yl) aniline. The presence of telomeric products in the reaction mixture is observed at a P/Pd ratio of 1:2 and 1:1. The use of (1,1,1‐trifluoro, 4‐perfluorocyclo hexyl ‐2,4‐butanedionato) palladium as the catalyst gives rise to 92 mol% mol.selectivity of telomers by the favored tail‐to‐head and head to head coupling.     

Effect of Different Ionic Liquids on 5-Hydroxymethylfurfural Preparation from Glucose in DMA over AlCl3: Experimental and Theoretical Study

In this work, effect of different ionic liquids (ILs) on 5‐hydroxymethylfurfural (HMF) preparation from glucose in N,N‐dimethylacetamide (DMA) over AlCl₃ was revealed by a combined experimental and computational study. ILs used as cocatalysts in this work included N‐methyl‐2‐pyrrolidone hydrogen sulfate ([NMP]HSO₄), N‐methyl‐2‐pyrrolidone methyl sulfate ([NMP]CH₃SO₃), N‐methyl‐2‐pyrrolidone chlorine ([NMP]Cl) and N‐methyl‐2‐pyrrolidone bromide ([NMP]Br) which were endowed with the same cation but different anions. According to the conclusion that fructose was intermediate product from glucose to HMF, we found fructose was transformed to more by‐products by [NMP]HSO₄, making HMF yield decline significantly when glucose was treated as substrate. Neither glucose nor fructose could be converted by [NMP]CH₃SO₃ efficiently, leading to its no influence on glucose conversion to HMF. [NMP]Br had a higher selectivity for HMF from fructose than [NMP]Cl and AlCl₃. Besides, Al³⁺ preferred to combine with Br^?, slightly decreasing both the overall free energy barrier for glucose isomerization and activation barrier for H‐shift at 393.15 K. So a high HMF yield of 57% was obtained from glucose catalyzed by AlCl₃ together with [NMP]Br under mild conditions.     

A Novel Synthetic Approach to (±)‐Desoxynoreseroline

(±)‐Desoxynoreseroline ( 3 ), the basic ring structure of the pharmacologically active alkaloid physostigmine ( 1 ), was synthesized starting from 3‐allyl‐1,3‐dimethyloxindole ( 9 ). The latter was prepared from the corresponding 2H‐azirin‐3‐amine 6 by a BF₃‐catalyzed ring enlargement via an amidinium intermediate 7 (Scheme 1). An alternative synthesis of 9 was also carried out by the reaction of N‐methylaniline with 2‐bromopropanoyl bromide ( 12 ), followed by intramolecular Friedel–Crafts alkylation of the formed anilide 13 to give Julian's oxindole 11 . Further alkylation of 11 with allyl bromide in the presence of LDA gave 9 in an excellent yield (Scheme 3). Ozonolysis of 9 , followed by mild reduction with (EtO)₃P, gave the aldehyde 14 , whose structure was chemically established by the transformation to the corresponding acetal 15 (Scheme 4). Condensation of 14 with hydroxylamine and hydrazine derivatives, respectively, gave the corresponding imine derivatives 16a – 16d as a mixture of syn‐ and anti‐isomers. Reduction of this mixture with LiAlH₄ proceeded by loss of ROH or RNH₂ to give racemic 3 (Scheme 5).     

The influence of sulfur substituents on the molecular geometry and packing of thio derivatives of N‐methylphenobarbital

The room‐temperature crystal structures of four new thio derivatives of N‐methylphenobarbital [systematic name: 5‐ethyl‐1‐methyl‐5‐phenylpyrimidine‐2,4,6(1H,3H,5H)‐trione], C₁₃H₁₄N₂O₃, are compared with the structure of the parent compound. The sulfur substituents in N‐methyl‐2‐thiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐2‐thioxo‐1,2‐dihydropyrimidine‐4,6(3H,5H)‐dione], C₁₃H₁₄N₂O₂S, N‐methyl‐4‐thiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐4‐thioxo‐3,4‐dihydropyrimidine‐2,6(1H,5H)‐dione], C₁₃H₁₄N₂O₂S, and N‐methyl‐2,4,6‐trithiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenylpyrimidine‐2,4,6(1H,3H,5H)‐trithione], C₁₃H₁₄N₂S₃, preserve the heterocyclic ring puckering observed for N‐methylphenobarbital (a half‐chair conformation), whereas in N‐methyl‐2,4‐dithiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐2,4‐dithioxo‐1,2,3,4‐tetrahydropyrimidine‐6(5H)‐one], C₁₃H₁₄N₂OS₂, significant flattening of the ring was detected. The number and positions of the sulfur substituents influence the packing and hydrogen‐bonding patterns of the derivatives. In the cases of the 2‐thio, 4‐thio and 2,4,6‐trithio derivatives, there is a preference for the formation of a ring motif of the R₂²(8) type, which is also a characteristic of N‐methylphenobarbital, whereas a C(6) chain forms in the 2,4‐dithio derivative. The preferences for hydrogen‐bond formation, which follow the sequence of acceptor position 4 > 2 > 6, confirm the differences in the nucleophilic properties of the C atoms of the heterocyclic ring and are consistent with the course of N‐methylphenobarbital thionation reactions.     

Phosphonic-Acid Analogues of the N-Acetyl-2-deoxyneiiraniinic Acids: Synthesis and Inhibition of Vibrio cholerae Sialidase

The phosphonic acids 3 and 4 were prepared to compare their inhibitory activity on Vibrio cholerae sialidase with the one of the corresponding N-acetyl-2-deoxyneuraminic acids 5 and 6 . Thus, hydrogenation and benzylation of methyl N-acetyl-2,3-didehydro-2-deoxyneuraminate (1MeNeu2en5Ac; 7) gave a mixture of the fully O-benzylated benzyl and methyl esters 9 and 10 , the partially O-benzylated benzyl and methyl esters 11 and 12 , and the fully O-and N-benzylated benzyl and methyl esters 13 and 14 (Scheme 1). Transesterification of 9 to 10 and hydrolysis of 10 gave the acid 15 . Oxidative decarboxylation of 15 with Pb(OAc)₄ gave a 1:9 mixture of the α-and β-D-glycero-D-galacto-acetates 16 and 17 . Phosphonoylation of 17 with P(OMe)₃ and Me₃SiOTf gave a 1.3:1 mixture of the phosphonates 18 and 19 , which were deprotected to give the (4-acetamido-2,4-dideoxy-D-glycero-α-and β-D-galacto-octopyranosyl)phosphonic acids 3 and 4 , respectively. The acid 6 was obtained by epimerization of the tert-butyl ester 23 with lithium N-cyclohexylisoproylamide and deprotection. The phosphonic acids 3 (K_i 5.5 10_-5 M) and 4 (K_i 2.3.10^?4 M ) are stronger inhibitors of Vibrio cholerae sialidase than the anomeric N-acetyl-2-deoxyneuraminic acids 5 (K_i 2.3 10^?3 M ) and 6 . Both 3 and 4 inhibit the Vibrio cholerae sialidase, while only the carboxylic acid 5 , possessing an equatorial COOH group is an inhibitor.     

Synthesis of 4‐alkyl‐1,2‐diphenyl‐3,5‐dioxopyrazolidines possessing aryl methylsulfonyl and sulfonamide pharmacophores for evaluation as selective cyclooxygenase‐2 (COX‐2) inhibitors

A group of 1,2‐diphenyl‐3,5‐dioxopyrazolidines possessing a methylsulfonyl ( 11 ) or sulfonamide ( 15 ) substituent at the para position of the N¹‐phenyl ring, in conjunction with a hydrogen, methyl or fluoro sub‐stituent at the para position of the N²‐phenyl ring, and a C‐4 n‐butyl, methyl or spiro‐cyclopropyl substituent were synthesized for evaluation as potential cyclooxygenase‐2 (COX‐2) selective inhibitor antiinflammatory agents. The title compounds 11 and 15 were synthesized using a four‐step and a three‐step reaction sequence, respectively. Thus, the acetic acid promoted condensation of a nitrosobenzene 5 with an aniline derivative ( 6, 12 ) gave the corresponding azobenzene product ( 8, 13 ) which was reduced with zinc dust in the presence of ammonium chloride to yield the corresponding hydrazobenzene ( 9, 14 ). Base‐catalyzed condensation of 9 and 14 with a malonyl dichloride ( 10 ) afforded the target 3,5‐dioxopyrazolidine product ( 11,15 ). 4‐n‐Butyl‐1‐(4‐methylsulfonylphenyl)‐2‐phenyl‐3,5‐dioxopyrazolidine ( 11a ) was a selective COX‐1 inhibitor (COX‐1 IC₅₀ = 8.48 μM). In contrast, 4‐n‐butyl‐1‐(4‐methylsulfonylphenyl)‐2‐(4‐tolyl)‐3,5‐dioxopyrazolidine ( 11b , COX‐2 IC₅₀ = 11.45 μM) and 4‐n‐butyl‐1‐(4‐methylsulfonylphenyl)‐2‐(4‐fluorophenyl)‐3,5‐dioxopyrazoli‐dine ( 11c , COX‐2 IC₅₀ = 9.86 μM) were about 46‐fold and 20‐fold less selective COX‐2 inhibitors respectively, relative to the reference drug celecoxib.     

Accurate binding energies of hydrogen,halogen, and dihydrogen bonded complexes and cation enhanced binding strengths

Interaction energy (E_int) values of a variety of hydrogen, halogen, and dihydrogen bonded complexes in the weak, medium, and strong regimes have been computed using W1BD, MP2, M06L density functional theory, and hybrid methods MP4//MP2, MP4//M06L, and CCSD(T)//MP2. W1BD level E_int and CCSD(T) results reported in the literature show very good agreement (mean absolute deviation = 0.19 kcal/mol). MP2 underestimates E_int while M06L shows accurate behavior for all except halogen and charge‐assisted hydrogen bonds. MP4//MP2, MP4//M06L, and CCSD(T)//MP2 yield E_int very close to those obtained from W1BD. The high accuracy energy data at MP4/MP2 is used to study the effect of a cation (Li⁺, NH₄⁺) on the E_int. The cation enhances electron donation from the donor to noncovalent bonding region leading to substantial enhancement in E_int (～141–566% for Li⁺ and ～105–539% for NH₄⁺) and promotes a noncovalent bond in the weak regime to medium regime and that in the medium regime to strong regime. © 2014 Wiley Periodicals, Inc.     

New route for preparation of nitrosubstituted 1,2‐phenylenediamines

4‐Nitrobenzoselenadiazole was methylated with dimethylsulphate to give corresponding 1‐N‐methyl‐4‐nitrobenzoselenadiazolium methylsulphate which after alkaline ring‐opening afforded 1‐N‐methyl‐3‐nitro‐1,2‐phenylenediamine in 90% yield. This compound was also prepared from 3‐nitro‐1,2‐phenylenediamine by monomethylation through tosylation, methylation and detosylation and was confirmed and characterised as 1‐methyl‐4‐nitrobenzimidazole. Methylation of 5‐nitrobenzoselenadiazole and subsequent alkaline ring‐opening led to unseparable mixture of both methylated products.     

Nickel(II) Complexes of Pentadentate N5 Ligands as Catalysts for Alkane Hydroxylation by Using m‐CPBA as Oxidant: A Combined Experimental and Computational Study

A new family of nickel(II) complexes of the type [Ni(L)(CH₃CN)](BPh₄)₂, where L=N‐methyl‐N,N′,N′‐tris(pyrid‐2‐ylmethyl)‐ethylenediamine (L1, 1 ), N‐benzyl‐N,N′,N′‐tris(pyrid‐2‐yl‐methyl)‐ethylenediamine (L2, 2 ), N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐(6‐methyl‐pyrid‐2‐yl‐methyl)‐ethylenediamine (L3, 3 ), N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐(quinolin‐2‐ylmethyl)‐ethylenediamine (L4, 4 ), and N‐methyl‐N,N′‐bis(pyrid‐2‐ylmethyl)‐N′‐imidazole‐2‐ylmethyl)‐ethylenediamine (L5, 5 ), has been isolated and characterized by means of elemental analysis, mass spectrometry, UV/Vis spectroscopy, and electrochemistry. The single‐crystal X‐ray structure of [Ni(L3)(CH₃CN)](BPh₄)₂ reveals that the nickel(II) center is located in a distorted octahedral coordination geometry constituted by all the five nitrogen atoms of the pentadentate ligand and an acetonitrile molecule. In a dichloromethane/acetonitrile solvent mixture, all the complexes show ligand field bands in the visible region characteristic of an octahedral coordination geometry. They exhibit a one‐electron oxidation corresponding to the Ni^II/Ni^III redox couple the potential of which depends upon the ligand donor functionalities. The new complexes catalyze the oxidation of cyclohexane in the presence of m‐CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity (A/K, 7.1–10.6, A=alcohol, K=ketone). Upon replacing the pyridylmethyl arm in [Ni(L1)(CH₃CN)](BPh₄)₂ by the strongly σ‐bonding but weakly π‐bonding imidazolylmethyl arm as in [Ni(L5)(CH₃CN)](BPh₄)₂ or the sterically demanding 6‐methylpyridylmethyl ([Ni(L3)(CH₃CN)](BPh₄)₂ and the quinolylmethyl arms ([Ni(L4)(CH₃CN)](BPh₄)₂, both the catalytic activity and the selectivity decrease. DFT studies performed on cyclohexane oxidation by complexes 1 and 5 demonstrate the two spin‐state reactivity for the high‐spin [(N5)Ni^II?O^.] intermediate (ts1_hs, ts2_doublet), which has a low‐spin state located closely in energy to the high‐spin state. The lower catalytic activity of complex 5 is mainly due to the formation of thermodynamically less accessible m‐CPBA‐coordinated precursor of [Ni^II(L5)(OOCOC₆H₄Cl)]⁺ ( 5 a ). Adamantane is oxidized to 1‐adamantanol, 2‐adamantanol, and 2‐adamantanone (3°/2°, 10.6–11.5), and cumene is selectively oxidized to 2‐phenyl‐2‐propanol. The incorporation of sterically hindering pyridylmethyl and quinolylmethyl donor ligands around the Ni^II leads to a high 3°/2° bond selectivity for adamantane oxidation, which is in contrast to the lower cyclohexane oxidation activities of the complexes.     

A Solid State Polymer‐Coated Electrode Containing a Chiral Crown Ether Derivative for Enantioselective Detection of Phenylglycine Methyl Ester Isomer

All solid‐state enantioselective electrode (ASESE) based on a newly synthesized chiral crown ether derivative ((R)‐(?)‐(3,3′‐diphenyl‐1,1′‐binaphthyl)‐23‐crown‐6 incorporating 1,4‐dimethoxybenzene) was prepared and characterized by potentiometry. The ASESE clearly showed enantiomer discrimination for methyl esters of alanine, leucine, valine, phenylalanine, and phenylglycine, where the enantioselectivity for phenylglycine methyl ester was the highest (K_R,S=8.5±7.1%). Experimental parameters of ASESE for the analysis of (R)‐(?)‐phenylglycine methyl ester were optimized. The optimized ASESE showed a slope of 55.3±0.2 mV/dec for (R)‐(?)‐phenylglycine methyl ester in the concentration range of 1.0×10^?5–1.0×10^?2 M and the detection limit was 9.0×10^?6 M. The ASESE showed good selectivity for (R)‐(?)‐phenylglycine methyl ester against inorganic cations and various amino acid methyl esters. The concentration of (R)‐(?)‐phenylglycine methyl ester was determined in the mixture of (R)‐(?) and (S)‐(+)‐phenylglycine methyl ester, which ratios varied from 2 : 1 to 1 : 9. The lifespan of the electrode was alleged to be 30 days.