Lewis Acid-Mediated Friedel-Crafts-Type Formylation of Alkenes with Dichloromethyl Methyl Ether in the Presence of Pyridines.

Various alkenes are formylated with dichloromethyl methyl ether (MOMCl2) by the combined use of SnCl4/2,6-dibromopyridine (B1) or AgOTf/pyridine (B4) via Friedel-Crafts-type reaction. The former reagent combination is mainly applied to α,α-diarylalkenes, while the latter one is applied not only to arylalkenes but also to some alkylalkenes. Vinyl aldehydes are exclusively obtained from alkenes that can possibly afford both allyl and vinyl aldehydes.

Synthesis of Azadioxa-Planar Triphenylboranes Bridged by Aryl- and Alkylimino Groups and Their Photophysical Properties.

Heteroatom-bridged planar triphenylboranes, in which the three phenyl groups are bridged at the ortho positions by heteroatoms, are attracting growing attention as one of the heteroatom-containing π-conjugated molecules. Herein, we developed the synthetic method of planar triphenylboranes bridged by two oxygen atoms and one nitrogen atom, and the substituent on the nitrogen atom is derived into various aryl and alkyl groups. A key intermediate bearing an imino group (-NH-) was synthesized from a bis-triflate precursor bridged by two oxo groups via a nucleophilic aromatic substitution reaction of benzyl amine and following debenzylation. The X-ray crystallographic analysis revealed that the compound exhibits a planar molecular structure which can form a one-dimensionally π-stacked structure. The photophysical and density functional theory studies revealed that their highest occupied molecular orbitals and lowest unoccupied molecular orbitals (LUMOs) are originated from the triphenylborane moiety, while introducing strong electron-withdrawing groups such as the 4-cyanophenyl group on the nitrogen atom can induce the localization of the LUMO at the aryl groups instead of the triphenylborane moiety.

Inclusion of Amine Isomers with Open-Chain Hosts Having a Partial Structure of p-tert-Butylthiacalixarene.

Porous materials, which can capture a specific compound from a hard-to-separate molecular mixture, are strongly desired for practical separation and purification processes. Aiming to develop such materials, we have investigated the performance of our original host compounds, [3,3'-thiobis(5-tert-butyl-2-hydroxybenzene)-1,1'-diyl]diacetic acid (2) and its monopropyl ester (3), in discriminating among regio- or stereoisomers of three groups of amines, 2-, 3-, and 4-methylpyridine, 2-, 6-, and 8-methylquinoline, and cis- and trans-4-cyclohexanamine. Diacid 2 selectively included 4-methylpyridine in hexane and 3-methylpyridine in toluene in competitive inclusion among the three regioisomers. Mechanistic studies revealed that the inclusions of 3- and 4-methylpyridine are favored under kinetic and thermodynamic control, respectively. Solvent-dependent switching in guest selectivity was also observed in competitive inclusion among the methylquinoline isomers with diacid 2, whereas trans-4-methylcyclohexanamine was selectively included over the cis-isomer by monoester 3, as well as diacid 2, regardless of the solvent employed. X-ray crystallographic analysis of the resulting inclusion crystals suggests that the wide guest scope of the host compounds originates from their flexible ability to form complexes with amines.

Extraction of Pd(ii) and Pt(ii) from aqueous hydrochloric acid with 1,3-diaminocalix[4]arene: switching of the extraction selectivity by using different extraction modes.

The extraction ability of 1,3-diaminocalix[4]arene (2: H2L) toward platinum group metals (PGMs) has been investigated, which revealed that 2 is able to extract Pd(ii) and Pt(ii) from hydrochloric acid via different extraction modes. The extraction species for Pd(ii) and Pt(ii) are [PdL] and [Pt2Cl6(H3L)2], respectively, as evidenced by equilibrium analysis and X-ray crystallography. In [PdL], the two phenoxide oxygens and two amino nitrogens of L2- coordinate to the Pd ion. On the other hand, in [Pt2Cl6(H3L)2], two anionic trichloro complexes PtCl3 - are sandwiched between two H3L+, in which one amino nitrogen directly coordinates to a PtCl3 - species and another protonated amino group forms an ion pair with another PtCl3 -. Utilizing the different extraction modes, switching of the extraction selectivity has been achieved in the competitive extraction between Pd(ii) and Pt(ii) by varying the concentrations of H+ and Cl- in the aqueous phase. Finally, from the extracted organic phase, back-extraction of Pd(ii) and Pt(ii) was easily performed, respectively.

Acylation of Alkenes with the Aid of AlCl3 and 2,6-Dibromopyridine.

Friedel-Crafts-type acylation of alkenes with acyl chlorides has been successfully conducted with a wide substrate scope by the combined use of AlCl3 and 2,6-dibromopyridine. Trisubstituted alkenes afford allylketones or vinylketones depending on the presence or absence of hydrogen atom(s) at the ß-position to the acylation site, while monosubstituted alkenes exclusively afford vinylketones.

Electrophilic Borylation of Terminal Alkenes with BBr3/2,6-Disubstituted Pyridines.

A variety of terminal alkenes, as well as heteroaromatic compounds, are borylated by the combined use of BBr3/2,6-dichloropyridine (B3) or BBr3/2,6-lutidine (B5). α,α-Diarylalkenes prefer the former reagent combination, while other alkenes prefer the latter. Mechanistic considerations strongly suggest that the former and latter reactions proceed through electrophilic substitution reactions with BBr3 and [BBr2·B5]+BBr4-, respectively.

Design and Synthesis of Open-Chain Hosts Having a Partial Structure of p-tert-Butylthiacalixarene.

The development of separation materials for hard-to-separate molecular mixtures is highly desired from environmental and economic perspectives. Although the crystal of p-tert-butylthiacalix[4]arene exhibits high guest selectivity in inclusion from a mixture of molecules with similar sizes and shapes, it cannot include molecules larger than its calix cavity. To extend its guest inclusivity, we designed and synthesized an open-chain host, [3,3'-thiobis(5-tert-butyl-2-hydroxybenzene)-1,1'-diyl]diacetic acid (4). The competitive inclusion among toluidine isomers using compound 4 gave inclusion crystals containing the p-isomer in 1:1 (host/guest) ratio, with lesser amounts of other isomers and/or solvent molecules. The isomer selectivity varied between 66% and 97% depending on the solvent employed. X-ray analysis of inclusion crystals 4·p-toluidine·MeCN and 4·p-toluidine·(o-toluidine)0.5 revealed that compound 4 includes p-toluidine by forming macrocyclic 2:2 inclusion complex(es) and that its higher-order structure has vacant spaces, in which molecules other than p-toluidine are included. Compound 4 was then transformed into monopropyl ester 5 to fill the vacant spaces with propyl moieties. Compound 5 included p-toluidine with high selectivity (∼96%) without the coinclusion of other molecules, regardless of the solvent employed.

Identification of number and type of cations in water-soluble Cs+ and Na+ calix[4]arene-bis-crown-6 complexes by using ESI-TOF-MS.

The treatment of cesium-contaminated wastewater has become one of the biggest issues. The selective Cs+ removal from wastewater containing competitive alkali metal ions such as Na+ is desired to reduce the volume of sludge. Therefore, the present work focused on water-soluble calix[4]arene-bis-crown-6 (W-BisC6) to selectively capture Cs+. For characterization of the complex, UV-vis spectroscopy is commonly used, however, due to the limited availability of information it can be hard to quickly identify the specific structures of some complexes. In this work, the electrospray ionization time of flight spectrometry (ESI-TOF-MS) is successfully utilized to identify the number and type of cations in W-BisC6-cation complexes. ESI-TOF-MS accurately recognized 4 types of complex (W-BisC6-Na+, W-BisC6-Cs+, W-BisC6-2Na+, W-BisC6-Na+-Cs+), and the experimental and simulated results were almost perfectly matched. It also revealed the difficulty of W-BisC6-2Cs+ complex formation under the present conditions. Thus, this technique is significantly helpful for rapid identification of the specific structures of complexes during Cs+-contaminated wastewater treatment.

EtAlCl2/2,6-Disubstituted Pyridine-Mediated Carboxylation of Alkenes with Carbon Dioxide.

α-Arylalkenes and trialkyl-substituted alkenes undergo carboxylation with CO2 in the presence of EtAlCl2 and 2,6-dibromopyridine to afford the corresponding α,ß- and/or ß,γ-unsaturated carboxylic acids. This reaction is suggested to proceed via the electrophilic substitution of EtAlCl2 with the aid of the base, followed by the carbonation of the resulting ate complex. This reaction can be applied to terminal dialkylalkenes by using a mixture of 2,6-di-tert-butylpyridine and 2,6-dibromopyridine.

Photoracemization of Blestriarene C and Its Analogs.

Two analogs of blestriarene C (4,4'-dimethoxy-1,1'-biphenanthrene-2,2',7,7'-tetraol) bearing no 7,7'-dihydroxy (3) and 4,4'-dimethoxy groups were prepared. Unlike blestriarene C (1), compounds and , as well as 1,1'-biphenanthrene-2,2'-diol (5), do not racemize under fluorescent lamp illumination. Cyclic voltammetry analysis reveals that compound has a lower half-wave potential (E(1/2)) than compounds , suggesting that a redox cycle is involved in the racemization. Compound racemizes by absorbing UV light corresponding to the (1) L(b) band. During the reaction, no side products are observed. The racemization is significantly inhibited under nitrogen. Based on these observations, we propose a feasible mechanism for the easy racemization of compound , which is mediated by a cation radical generated in situ by a reversible photo-induced oxygen oxidation.

1,3-Diiodocalix[4]arene: synthesis by Ullmann-type iodination of 1,3-bistriflate ester of calix[4]arene, conformational analysis, and transformation into 1,3-dicarboxy-, diformyl-, and dialkylcalix[4]arenes.

A facile synthesis of 1,3-diiodocalix[4]arene 6 has been achieved by copper-catalyzed iodination of the 1,3-bistriflate ester 2a of p-tert-butylcalix[4]arene. After protection of the hydroxy groups with iodomethane, diiodide 6 is subjected to halogen­lithium exchange with butyllithium, followed by carbonation with CO2 or formylation with N-formylpiperidine and subsequent deprotection of the hydroxy groups to give novel dicarboxylic acid 11 or dialdehyde 16 in practical yields. The iodo groups of diiodide 6 pass through the calixarene macrocycle; the activation free energy for the conversion of the more stable syn conformer 6syn to the less stable anti conformer 6anti is ΔG(⧧) = 104 kJ mol(­1) at 298 K. Dialdehyde 16 shows fast self-exchange between two equivalent species with a cone conformation, ΔG(⧧), being 63.2 kJ mol(­1). Dicarboxylic acid 11 adopts a cone conformation and forms a dimer in solution as suggested by 1H NMR and X-ray crystallographic analyses. The arrangement of the iodide groups of compound 6 can be fixed predominantly to anti (17a and 17b) by introducing bulky alkyl groups (e.g., propyl groups) onto the hydroxy groups. The stereospecific alkylation of the iodo groups of the resulting di-O-alkylated anti-1,3-diiodides provides access to the anti-1,3-dialkylcalixarenes 19, which is otherwise difficult to obtain.

Effect of solvent polarity on enantioselectivity in Candida antarctica lipase B catalyzed kinetic resolution of primary and secondary alcohols.

The Candida antarctica lipase B (CAL-B) catalyzed kinetic resolution of primary and secondary alcohols via acetylation is dependent on the permittivity (ε) of the reaction solvent. For example, the enantiomeric ratio (E) vs ε plot for the acetylation of 1-(naphth-2-yl)ethanol (1) exhibits a convex shape, taking the maximum E value at a medium ε value (11.2), whereas the same plot for the acetylation of benzyl 3-hydroxybutylate (3) exhibits a concave shape, taking the minimum E value at a similar ε value (11.6). Kinetic studies reveal that the difference in shape of the E vs ε plots originates from the relative reaction rate between the enantiomers with different Michaelis constants (Km). Thus, when the enantiomer with a larger Km value in the middle ε region reacts more slowly than its antipode, the ε dependence of E exhibits a convex shape. On the other hand, when the enantiomer reacts more quickly, it exhibits a concave shape. The E vs ε plot for the acetylation of 2-methoxy-2-phenylethanol (7) exhibits a convex shape with the maximum E value (20) at ε = 14.1. The E value can be further improved to almost reach the efficiency required for industrial applications (E ≈ 30) by the addition of a nitro compound.

Switching of the diastereomer deposited during the crystallization of N-[(S)-1-phenylethyl]-2'-carbamoyl-1,1'-binaphthalene-2-carboxylic acid: investigation of the mechanism of dielectrically controlled resolution.

Dielectrically controlled resolution (DCR) has been achieved during the crystallization of (S)-1-phenylethylamides of racemic 1,1'-binaphthalene-2,2'-dicarboxylic acid (RS(a),S)-1. For example, a water well-shaped plot is obtained for the diastereomeric excess (de) of the deposited amide versus the solvent permittivity (ε) for the crystallization of (RS(a),S)-1 from three-component mixed solvents, consisting of 25 vol % of dichloromethane and 75 vol % of varying ratios of two solvents (i.e., an alcohol and either hexane or water). The de value drastically changes within two narrow ε ranges and diastereomerically pure crystals of either (R(a),S)-1 (13.9 ≤ ε ≤ 17.9) or (S(a),S)-1·CH(2)Cl(2) (ε ≤ 11.9 and ε ≥ 21.8) deposit, depending on the solvent permittivity. X-ray crystallographic analyses reveal that the major difference between the crystal structures of (S(a),S)-1 and (R(a),S)-1 is the presence of solvent molecules that fill the spatial voids in the (S(a),S)-1 crystals. The ε-dependence of the chemical shifts of (S(a),S)-1 and (R(a),S)-1 suggests that their aggregation states are similar in the same solvents and change discontinuously at two ε values. The ε-dependence of the C═O stretching vibrations suggests that the lower ε is a transition point where the amide molecules, which aggregate through intermolecular hydrogen bonds in low-permittivity solvents, begin to dissociate. An absorption experiment suggests that dichloromethane is easily incorporated into solvent-free (S(a),S)-1 crystals in high-permittivity solvents. On the basis of these observations, a feasible molecular mechanism is proposed for the present DCR phenomenon.

Unique inclusion properties of crystalline powder p-tert-butylthiacalix[4]arene toward alcohols and carboxylic acids.

Powdery crystals of p-tert-butylthiacalix[4]arene (2) selectively include EtOH from 1:1 mixtures of MeOH-EtOH and EtOH-PrOH, and EtCO(2)H from HCO(2)H-EtCO(2)H. On the other hand, no acid is included from HCO(2)H-MeCO(2)H, even though MeCO(2)H is included from the neat acid. The origins of these phenomena are discussed based on X-ray analysis of inclusion crystals prepared separately by crystallization.

Synthesis of mono- and 1,3-diaminocalix[4]arenes via Ullmann-type amination and amidation of 1,3-bistriflate esters of calix[4]arenes.

Practical methods are described for the preparation of monoamines 4 and 1,3-diamines 5, bearing one or two amino group(s) instead of the hydroxy group(s) at the 28-position or at both the 26- and 28-positions of p-tert-butylcalix[4]arene (1a) and p-tert-butylthiacalix[4]arene (1b), via the Ullmann-type amination or amidation. Thus, the copper-catalyzed or mediated amination of the 1,3-bistriflate ester (2a) of 1a with benzylamine affords either mono(benzylamino) triflate 7a or 1,3-bis(benzylamine) 8 in a high yield, depending on the reaction conditions. On the other hand, the 1,3-bistriflate ester (2b) of 1b resists disubstitution and produces, under stoichiometric conditions, mono(benzylamino) triflate 7b. The disubstitution of 2b is achieved by amidation with tosylamide, giving 1,3-bis(tosylamide) 17b. The hydrogenolysis of the benzylamino moiety of 7a, followed by the hydrolysis of the Tf moiety, affords monoamine 4a, while the hydrogenolysis of 8 affords 1,3-diamine 5a. The amino moiety of 7b can be deprotected under acidic conditions to give, after hydrolysis, monoamine 4b. The hydrolysis of 17b affords 1,3-diamine 5b. The overall yields of compounds 4a, 4b, 5a, and 5b are 72%, 45%, 78%, and 24%, respectively, based on commercially available compounds 1 and are much higher than the ones previously reported in the literature.

Direct carboxylation of arenes and halobenzenes with CO2 by the combined use of AlBr3 and R3SiCl.

The Lewis acid-mediated direct carboxylation of aromatic compounds with CO2 is efficiently promoted by the addition of silyl chlorides bearing three alkyl and/or aryl substituents in total on the silicon atom. Thus, toluene, xylenes, mesitylene, and some other alkylbenzenes are treated with a 1:1 mixture of AlBr3 and Ph3SiCl in neat substrates under CO2 pressure (3.0 MPa) at room temperature, to give the corresponding carboxylic acids in 60-97% yields, based on AlBr3. Polycyclic arenes, including naphthalene, phenanthrene, and biphenyl, are regioselectively carboxylated in 91-98% yields with the aid of 1 molar equiv of AlBr3 and Ph3SiCl in an appropriate solvent, chosen from benzene, chlorobenzene, and fluorobenzene. These solvents, as well as bromobenzene, resist carboxylation; however, they are also carboxylated in moderate yields when treated with a 1:5 mixture of AlBr3 and (i)PrSiCl at elevated temperatures. The FT-IR spectrum of a mixture prepared by exposing a suspension of AlBr3 and Ph3SiCl in cyclohexane to CO2 exhibits an absorption band around 1650 cm(-1), assigned to the C═O stretching vibration of a species consisting of CO2, AlBr3, and Ph3SiCl, which suggests that the silyl chlorides activate CO2 in cooperation with AlBr3. (1)H NMR analysis of unworked-up reaction mixtures reveals that the products merge as aluminum carboxylates. The mass balance concerning silicon indicates that the silyl chlorides are recycled during the reaction sequence. On the basis of these observations, a feasible mechanism is proposed for the present carboxylation.

Synthesis of dinuclear boron complexes of sulfinylcalix[4]arenes: Syn/Anti stereocontrol by the arrangement of the sulfinyl functions.

Stereocontrol in the synthesis of dinuclear metal complexes of sulfinylcalix[4]arenes 2 has been achieved by the arrangement of sulfinyl functionalities. Thus, the treatment of the(rtct) isomer of 2 (2(rtct)) with an excess of Et(3)B affords syn dinuclear boron complex 4, while a similar treatment of rctt and rcct isomers 2(rctt) and 2(rcct) yields anti dinuclear complexes 5 and 6, respectively.

Simple and effective 3D recognition of domoic acid using a molecularly imprinted polymer.

We have developed a simple and effective molecular imprinting technique to target compounds with flexible structure. Domoic acid (DA), an amnesic shellfish poison, was used as the target compound while many acidic compounds (mono-, di-, and tricarboxylic acids) were used as template molecules for molecularly imprinted polymers (MIPs). Evaluation of selective recognition abilities using liquid chromatography revealed that the highest selective recognition ability for DA was found when pentane-1,3,5-tricarboxylic acid (1,3,5-PeTA) was used as the template. Computer modeling studies of the DA structure suggested that the observed selective recognition depended on the structural changes in DA at the recognition site of the MIPs as well as spatial distance between the COOH groups in DA and 1,3,5-PeTA. Using the 1,3,5-PeTA-MIP, we could easily purify DA from blue mussel extracts by solid-phase extraction.

Conformational behaviors of tetra-O-methylsulfinylcalix[4]arenes--an approach to control the conformation of thiacalix[4]arenes by oxidizing sulfur bridges.

The conformational behaviors of all four stereoisomers [5(rctt), 5(rcct), 5(rtct), and 5(rccc)] of tetra-O-methylsulfinylcalix[4]arene were studied by the 1H NMR spectroscopic method. Variable-temperature (VT) NMR experiments of 5(rctt), 5(rcct), and 5(rtct) revealed that each compound adopted the same conformation as that in the crystals at low temperatures and exhibited a self-exchange between the two equivalent species of this conformation at elevated temperatures. The values of the activation enthalpy DeltaH for the self-exchange were similar (approximately 70 kJ mol-1). Further, the activation entropy DeltaS++ was more important for 5(rtct) (-40 J mol-1 K-1) than for 5(rctt) (-5 J mol-1 K-1) and 5(rcct) (-7 J mol-1 K-1); consequently, the exchange rate of 5(rtct) was 150-180 times less than that of the other isomers at 273 K. On the other hand, 5(rccc) was in an equilibrium state between cone and partial-cone conformers at 253 K with the molar ratio being 85:15, which was in reasonable agreement with the relative stability between the two conformers calculated by the ab initio molecular orbital method.