Mechanism of BPh3-Catalyzed N-Methylation of Amines with CO2 and Phenylsilane: Cooperative Activation of Hydrosilane

BPh₃ catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO₂ and PhSiH₃; these reactions proceed at 30–40 °C under solvent-free conditions. In contrast, B(C₆F₅)₃ shows little or no activity. ¹¹B NMR spectra suggested the generation of [HBPh₃]⁻. The detailed mechanism of the BPh₃-catalyzed N-methylation of N-methylaniline ( 1 ) with CO₂ and PhSiH₃ was studied by using DFT calculations. BPh₃ promotes the conversion of two substrates (N-methylaniline and CO₂) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N⁺CO₂⁻⋅⋅⋅BPh₃]. The carbamate and BPh₃ act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH₃ to generate [HBPh₃]⁻, which is used to produce key CO₂-derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1 . DFT calculations also suggested other mechanisms involving water for the generation of [HBPh₃]⁻ species.     

Thermal stability of phthalate esters: Effect of substituents on the β-carbon atom

In order to clarify the mechanism conferring heat resistance on phthalate esters, those with a substituent on the β-carbon atom, such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate and dineopentyl phthalate, were synthesized and their thermal stabilities were studied by thermogravimetry and differential thermal analysis. The analytical results for these phthalate esters were compared with those for dibutyl phthalate, with a straight alkyl chain. As the temperatures required for a 3% weight loss of phthalate esters with a substituent, an electron-donating group (amino group) or an electron-accepting group (nitro group) on the β-carbon atom move to the higher end of the range, the effect of the adjacent group was recognized. The presence of a phenyl group in phthalate esters considerably improved the heat resistance. It is considered that the high heat resistance of bis(2,4-diphenylbutyl) phthalate is due to the obstruction of the planar configuration for cis elimination by the phenyl group and hindrance by the phenyl group of the formation of the six-membered cyclic transition state owing to the interaction between non-bondable molecules.     

Reaction of 3,4-disubstituted 1,2,5-oxadiazole 2-oxides with dipolarophiles : Substituent and solvent effect on the reaction courses

A variety of symmetrically or unsymmetrically 3,4-disubstituttd furoxans such as dicyano, dialkyl, diacyl, bis(phenylsulfonyl), N.N'-dialkyldicarbamoyl, 3(or 4)-methyl-4(or -3)-phenyl(or nitro, ethoxy, phenoxy, phenylthio, pyrrolidinyl, phenylsulfonyl), 3(or 4)-ethyl-4(or -3)phcnyl, and 3(or 4)-ethoxy-4(or -3)-phenylsulfonylruroxan reacted with dipolarophiles in toluene or xylene at the refluxing temperature to give nitrone-type 1,3-dipolar cycloadducts, 5-substituted 1-aza-2,8-dioxabicyclo-[3.3.0]octanes and/or 3-substituted 2-isoxazoline 2-oxides. On the other hand, some of the furoxans gave 2-isoxazolines via nitrile oxide 1,3-dipolar cycloaddition in a toluene (or xylene)-DMF solvent at the refluxing temperature.     

Electrochemical Fluorination of Dithiocarbonates Using a Triarylamine Mediator

Electrochemical oxidation of O-(4-chlorobenzyl) S-methyl dithiocarbonate using tris(2,4-dibromophenyl)amine as a redox mediator was studied by cyclic voltammetric measurements. The triarylamine mediated anodic fluorodesulfurization of O-(4-chlorobenzyl) and O-(4-bromobenzyl) S-methyl dithiocarbonates provided 4-chloro- and 4-bromobenzyl fluorides, respectively in moderate yields. On the other hand, similar anodic fluorination of O-(2-phenethyl) S-octyl dithiocarbonate and O-(4-bromophenyl) S-methyl dithiocarbonate afforded 2-phenethyl trifluoromethyl ether and difluoro(methylthio)methyl 4-bromophenyl ether, respectively. Mechanistic aspects are also discussed.     

Furopyridines. XXIII. Synthesis and reactions of chloropyridine derivatives of furo[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine

Chlorination of the N-oxides of furo[2,3-b]- 1a , -[2,3-c]- 1b and -[3,2-c]pyridine 1c with phosphorus oxychloride afforded compounds substituted normally at the α- or λ-position to the ring nitrogen, 2a, 2′a, 2b, 2c, 2′c and 2′c , and in addition, in the case of 1b , compounds substituted on the furan ring, 2′b and 2″b . The structures of these compounds were confirmed from their ir, nmr and mass spectra. The major chlorinated products 2a, 2b and 2c were converted to methoxy- 5a, 5b and 5c , N-pyrrolidyl- 7a, 7b and 7c , and phenylthiofuropyridines 8a, 8b , and 8c .     

Surface treatment of silicon carbide using TiO2(IV) photocatalyst

Silicon carbide (SiC) and diamond were decomposed to CO(2)(g) by the photocatalysis with TiO(2) at room temperature, although the decomposition rate of diamond was very slow. According to the XPS spectra of Si2p on the SiC surface, SiO(2) was simultaneously formed on the surface by the TiO(2) photocatalysis. The thickness of the SiO(2) formed on the SiC surface during the photocatalytic oxidation for 1 h was estimated to be about 40 A from the depth profile of the XPS spectra using Ar etching. The SiC surface was oxidized by the TiO(2) photocatalysis even under the condition without a direct contact with the TiO(2). This indicates that the photocatalytic oxidation of the SiC occurs due to active oxygen species photogenerated on the TiO(2) surface, but not by hole produced in the valence band of the TiO(2). Moreover, a remote surface treatment system using the quartz beads coated with TiO(2) was developed for the SiC surface oxidation. Consequently, the TiO(2) photocatalysis will be very useful for the surface treatment of SiC such as photopatterning without defects and damage to the substrate because the photocatalytic reaction is carried out under mild conditions.     

Crystalline orientation of the InN films prepared by atmospheric pressure halide chemical vapor deposition

The structural analysis of the hexagonal InN film prepared on a Si(100) substrate by the AP-HCVD technique using InCl₃ and NH₃ as starting materials were carried out by the X-ray pole figure analysis. The deposited films consist of the hexagonal InN pillar crystals. It was found that the pillar crystals, which have random rotation around the 100 axis, were grown at an angle of 70–90° to the substrate.     

Swelling of poly(ethylene oxide) gel in aqueous solutions of sodium dodecyl sulfate with added sodium chloride

The swelling behavior of poly(ethylene oxide) (PEO) gels in aqueous solutions of sodium dodecyl sulfate (SDS) with and without NaCl was investigated. In the absence of NaCl, PEO gels with different degrees of cross-linking began to swell from a concentration lower than the critical micelle concentration (cmc) of SDS, then showed sigmoidal enhancements of swelling in a higher SDS concentration region until the degrees of swelling reached maximum values. The SDS concentration at which the swelling began to appear was in reasonable agreement with the critical aggregation concentration (cac) value reported for the aqueous PEO system. For the cases where NaCl was present, the swelling behavior of PEO gel was different from that when NaCl was absent in the following way. The concentrations where the swelling begins to appear, and hence those where the degree of swelling rises steeply, decreased with an increase in NaCl concentration. The ultimate degrees of swelling at higher concentration regions also decreased with an increase in the NaCl concentration. The lowering of the SDS concentrations at which the PEO gel began to swell is in line with the decreases in the cmc of SDS solutions containing NaCl and also with the decreases in the cac of PEO solution. Electronic Publication     

First enantioselective synthesis of salinipostin A,a marine cyclic enol-phosphotriester isolated from Salinispora sp

Salinipostins are cyclic enol-phosphotriesters isolated from a marine-derived Salinispora sp. as antimalarial compounds. Herein, the first enantioselective synthesis of salinipostin A was achieved. Organocatalyst-mediated asymmetric cyclopropanation and regioselective cyclopropane ring opening were the key steps.     

Unexpected Macrocyclic Multinuclear Zinc and Nickel Complexes that Function as Multitasking Catalysts for CO2 Fixations

Unique self‐assembled macrocyclic multinuclear Zn^II and Ni^II complexes with binaphthyl‐bipyridyl ligands (L) were synthesized. X‐ray analysis revealed that these complexes consisted of an outer ring (Zn₃L₃ or Ni₃L₃) and an inner core (Zn₂ or Ni). In the Zn^II complex, the inner Zn₂ part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO₂ fixations: synthesis of cyclic carbonates from epoxides and CO₂ and temperature‐switched N‐formylation/N‐methylation of amines with CO₂ and hydrosilane.