A number of SO3H-functionalized solids (biochar, montmorillonites, carbon and halloysite nanotubes) has been studied as catalysts in the cascade Prins-Ritter reaction of (-)-isopulegol with ...benzaldehyde and acetonitrile for synthesis of octahydro-2H-chromene amides (as 4R- and 4S-isomers). A high selectivity to these products at 30 °C in the presence of H2O was observed on catalysts modified with chlorosulfonic acid (CSA) reaching 84% (4R/4S of 5.7) in the case of biochar, while a relatively large amount of octahydro-2H-chromenols (up to 31%), products of Prins condensation, was formed on the materials functionalized by 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSP). Although Prins condensation proceeds efficiently on weak acid sites, the Prins-Ritter reaction requires sulfated materials with strong (0.33 – 5.8 mmol/g) Brønsted acidity. Catalysts functionalized by CSP were stable, while for the materials modified with chlorosulfonic acid, leaching of -SO3H groups was observed. Nonetheless, on resistant Bioсhar-CSP, selectivity to the amides at 30 °C (67%) was higher than that with the commercial Amberlyst-15 (47%), and triflic acid at − 25 °C (62%). Similar selectivity to the desired products on Biochar-CSA (-SO3H groups) and H2SO4 (81–84%) as well as on Biochar-CSP (-PhSO3H) and with p-toluenesulfonic acid (67–70%) was observed. DFT calculations and experimental results showed that at 30 °C formation of 4S-amide thermodynamically is more beneficial than of alcohols and dehydration products. However, addition of water results in a sharp increase in the reaction rate and 4R-amide selectivity due to a change to the kinetic control, leading eventually to both high yields and stereoselectivity. The proposed reaction pathways also were confirmed by kinetic modelling.
Display omitted
•Heterogeneous and homogeneous catalysts for the Prins-Ritter reaction at ambient conditions.•The reaction requires sulfated materials with strong Brønsted acidity.•Selectivity to amides up to 84% (4 R/4 S of 5.7) on Biochar-CSA or sulfuric acid.•Formation of 4S-amide is thermodynamically more favorable.•Addition of water results in a kinetic control with high stereoselectivity.
Display omitted
•Condensation of (–)-α-pinene with formaldehyde into 8-acetoxy-6-hydroxymethyllimonene.•Selectivity of 24 % with traditional Lewis and Brønsted acids (ZnCl2, FeCl3, H3PO4).•Comparable ...selectivity for strongly acidic H-Beta-25 zeolite and phosphoric acid.•Reaction mechanism elucidated using kinetic and quantum chemical approaches.•Successful scaling up 8-acetoxy-6-hydroxymethyllimonene synthesis.
While synthesis of hydroxymethyl derivatives of common terpenes by a reaction with formaldehyde (FA) has been commercialized, no open data are available on the preparation of such α-pinene derivatives. Here, an approach for the renewable (–)-α-pinene catalytic utilization by its condensation with FA into a novel terpenoid 8-acetoxy-6-hydroxymethyllimonene is proposed. Both common homogeneous acids and aluminosilicates (halloysite nanotubes pretreated with H3PO4 and HCl, montmorillonite K-10, zeolite H-Beta-25) have been investigated. The solids were characterized by SEM, EDX, 27Al and 29Si MAS NMR, as well as FTIR with pyridine and N2 adsorption–desorption methods. Traditional Lewis and Brønsted acids (ZnCl2, FeCl3, H3PO4 etc.) catalyzed the desired condensation although selectivity did not exceed 24 % in the case of phosphoric acid due to the side reactions, including opening of the α-pinene cyclobutane ring, as well as skeletal rearrangements of its bicyclic structure. On aluminosilicates with a weak to moderate Lewis and Brønsted acidity (45–104 µmol/g), the products of a direct substrate protonation (up to 52.8 %) were predominantly formed. In the presence of strongly acidic H-Beta-25 (301 µmol/g) and phosphoric acid, selectivity to α-pinene addition products with formaldehyde (32.3–35.3 %) and substrate direct protonation (30.0–36.8 %) were comparable. However, with H3PO4 the content of borneol derivatives formed via the Wagner-Meerwein rearrangement was the smallest (13.5 %) giving subsequently the largest selectivity to the desired 8-acetoxy-6-hydroxymethyllimonene. Higher selectivity to the target product was observed at lower reaction temperature and a larger formaldehyde amount. The reaction mechanism has been proposed and elucidated using kinetic and quantum chemical approaches. The developed kinetic model adequately describes the experimental results. The DFT calculations showed that in the presence of H3PO4 there are no significant differences between the energy of the intermediates formed due to formaldehyde addition to α-pinene or its direct protonation. Synthesis of 8-acetoxy-6-hydroxymethyllimonene was performed on 22 g scale. This compound can be considered as a chiral platform for further utilization, including synthesis of heterocyclic compounds.
In this paper, we describe the current state of development of a prototype detector for the study of fast processes (DIMEX) based on a silicon microstrip sensor. The silicon microstrip sensor is made ...of
n
-type silicon with
p
-type implants in the form of strips. Aluminum contacts with microwelding pads at the ends are applied to the strips along the entire length. The signals from the strips are read using a DMXS6A integrated circuit specially designed for this project, which contains six recording electronic channels with a dark-current compensation circuit at the input, four integrators, 32 analog memory cells, and an analog shift register. Each sensor strip is connected to the guard ring through a 400-Ω resistor and to the recording-channel input through a 100-kΩ resistor. This resistive divider at the input of the recording channel makes it possible to adapt the dynamic range of the recording microcircuit integrator to the full range of photon-flux changes in synchrotron-radiation output channel no. 8 of the VEPP-4M storage ring equipped with a nine-pole wiggler with a field of 1.95 T as the source of synchrotron radiation. Measurements of the dynamic range of the DIMEX-Si prototype show that the maximal flux that can be recorded in the linear mode exceeds 10
5
photons/channel from each electron bunch in the storage ring. The ability of the detector to detect signals from bunches following after 55 ns in the multi-bunch mode, which simulates the operation of the 4+-generation synchrotron-radiation source Siberian Circular Photon Source (SKIF) under construction in the Novosibirsk region, on which such a detector is planned to be used, is also demonstrated.
The development of highly efficient methods for the synthesis of chemical products by using renewable raw materials is one of the topical areas of medicinal chemistry. The paper presents the ...synthesis of (2aR,2a1S,5aR,9bR)-4-isopropyl-7,8-dimethoxy-2a1-methyl-2,2a,2a1,3,5a,9b-hexahydrofluoreno9,1-bcfuran. The title compound was obtained through Prins–Friedel–Crafts cascade reactions of trans-4-hydroxymethyl-2-carene, which was synthesized from 3-carene, one of the main components of gum turpentine. The product yield after purification was 48%. The compound’s structure was confirmed by X-ray diffraction analysis.
The work describes a one-dimensional detector for diffraction experiments at a synchrotron radiation beam. The detector is being developed at the Budker Institute of Nuclear Physics, Siberian Branch, ...Russian Academy of Sciences. Until recently the institute was developing gas one-coordinate detectors, in particular a one-coordinate detector with calculated channels (OD-3M), based on the technology of multiwire proportional chambers. To provide a spatial resolution better than 100 microns at a photon energy in a wide energy range (3–30 keV), it is necessary to use solid-state microstrip or matrix sensors in combination with specialized integrated registration circuits. The developed SOCOD detector, using a microstrip sensor based on gallium arsenide as a registration element, operates in the mode of the direct counting of photons with an energy of more than 3–4 keV and a speed of up to 1 MHz/channel. The work gives a general description of the current version of the detector, a block diagram of the registration channel, the software allowing users to control the operation of the detector and display the results obtained, and the developed algorithm for leveling the trigger thresholds in the channels. The results of electronic tests, the work of the alignment algorithm and their discussion are presented.
We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| using the decay B → Dℓνℓ (ℓ = e,μ) based on 711 fb–1 of e+e– → Υ(4S) data recorded by the Belle ...detector and containing 772 × 106 BB¯ pairs. Here, one B meson in the event is fully reconstructed in a hadronic decay mode, while the other, on the signal side, is partially reconstructed from a charged lepton and either a D+ or D0 meson in a total of 23 hadronic decay modes. The isospin-averaged branching fraction of the decay B → Dℓνℓ is found to be B(B0 → D–ℓ+νℓ) = (2.31 ± 0.03(stat) ± 0.11(syst))%. Analyzing the differential decay rate as a function of the hadronic recoil with the parametrization of Caprini, Lellouch, and Neubert and using the form-factor prediction G(1) = 1.0541 ± 0.0083 calculated by FNAL/MILC, we obtain ηEW|Vcb| = (40.12 ± 1.34) × 10–3, where ηEW is the electroweak correction factor. Alternatively, assuming the model-independent form-factor parametrization of Boyd, Grinstein, and Lebed and using lattice QCD data from the FNAL/MILC and HPQCD collaborations, we find ηEW|Vcb| = (41.10 ± 1.14) × 10–3.
Using the entire Belle data sample of 980 fb−1 of e+e− collisions, we present the results of a study of excited Ωc charmed baryons in the decay mode Ξc+K−. We show confirmation of four of the five ...narrow states reported by the LHCb Collaboration: the Ωc(3000), Ωc(3050), Ωc(3066), and Ωc(3090).
PDF
