Three-component coupling based on the "cation pool" method

Sequential one-pot three-component coupling reactions have been developed based on the "cation pool" method. An N-acyliminium ion generated by the "cation pool" method adds to an electron-rich carbon-carbon double bond, such as enamine derivatives and vinyl sulfides, to form the second "cation pool". The addition of nucleophiles such as allylsilanes, enol silyl ethers, Grignard reagents, and organoaluminum compounds led to the formation of the corresponding three-component coupling products.     

Indirect cation pool method. Rapid generation of alkoxycarbenium ion pools from thioacetals

A sequential one-pot indirect cation pool method has been developed. The method involves the electrochemical generation and accumulation of ArS(ArSSAr)+ at low temperature (step 1) and the follow-up reaction with a thioacetal to generate an alkoxycarbenium ion pool (step 2), which reacts with various carbon nucleophiles (step 3). Steps 2 and 3 are extremely fast. The electrogenerated ArS(ArSSAr)+ was well-characterized by 1H NMR and CSI-MS. The alkoxycarbenium ion pool generated by the present indirect method exhibited 1H and 13C NMR spectra and thermal stability similar to those of the alkoxycarbenium ion pool generated by the direct electrochemical method.     

Reduction of a "cation pool": a new approach to radical mediated C--C bond formation.

Carbocations, carbon radicals, and carbanions are important reactive carbon intermediates in organic chemistry, and their interconversions can be carried out by redox processes. Although, such relationships have been well recognized, experimental work has been limited to analytical studies on highly stabilized intermediates. In this study such interconversions were examined using electrochemical reduction of "cation pools". Acyliminium cations, which were generated by low-temperature electrolysis of carbamates, were reduced electrochemically in the absence of radical acceptors. The homo coupling products formed effectively, suggesting that the one-electron reduction of the acyliminium cation produced the corresponding carbon-centered radical. Next, the electrochemical reduction of the acyliminium cations in the presence of electron-deficient olefins was examined. The cross coupling products were obtained in good-to-moderate yields. A mechanism involving radical addition to the double bond followed by the reduction of the resulting radical to the carbanion was suggested. The overall transformation serves as redox-mediated formal addition of C-H to C=C. The present strategy opens new opportunities to manipulate reactive carbon species using redox processes in organic synthesis.     

Generation of alkoxycarbenium ion pools from thioacetals and applications to glycosylation chemistry

[reaction: see text] Alkoxycarbenium ions have been generated and accumulated as "cation pools" by the low-temperature electrochemical oxidation of alpha-phenylthioethers. Although an unsuccessful attempt to accumulate glycosyl cations was made, a one-pot method for electrochemical glycosylation, which involves anodic oxidation of thioglycosides to generate glycosyl cation equivalents followed by their reactions with glycosyl acceptors, has been developed.     

Integrated electrochemical-chemical oxidation mediated by alkoxysulfonium ions

Generation of carbocations by the "cation pool" method followed by reaction with dimethyl sulfoxide (DMSO) gave the corresponding alkoxysulfonium ions. Alkoxysulfonium ions could also be generated by in situ DMSO trapping of electrochemically generated carbocations. The resulting alkoxysulfonium ions were transformed into carbonyl compounds by treatment with triethylamine. The present integrated electrochemical-chemical oxidation can be applied to the oxidation of diarylmethanes to diaryl ketones, toluenes to benzaldehydes, and aryl-substituted alkenes to 1,2-diketones. Moreover, the oxidation of unsaturated compounds bearing a nucleophilic group in an appropriate position gives cyclized carbonyl compounds.     

Current State of Microflow Trifluoromethylation Reactions

The trifluoromethyl group is a powerful structural motif in drugs and polymers; thus, developing trifluoromethylation reactions is an important area of research in organic chemistry. Over the past few decades, significant progress has been made in developing new methods for the trifluoromethylation of organic molecules, ranging from nucleophilic and electrophilic approaches to transition-metal catalysis, photocatalysis, and electrolytic reactions. While these reactions were initially developed in batch systems, more recent microflow versions are highly attractive for industrial applications owing to their scalability, safety, and time efficiency. In this review, we discuss the current state of microflow trifluoromethylation. Approaches for microflow trifluoromethylation based on different trifluoromethylation reagents are described, including continuous flow, flow photochemical, microfluidic electrochemical reactions, and large-scale microflow reactions.     

One-electron reduction of an "extended viologen" p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium) dication

One-electron reduction of the "extended viologen" dication 1 yields the red cation radical 2, characterized by strong near-IR absorption. It has been generated and studied by pulse radiolytic, electrochemical, redox titration, UV-visible, and electron paramagnetic resonance spectroscopic methods. All results are in agreement with a fully delocalized electronic structure for 2.     

Evaluation of the antioxidant activity by flow injection analysis method with electrochemically generated ABTS radical cation

A Trolox equivalent antioxidant capacity (TEAC) decolourisation assay was adapted to a flow injection analysis (FIA) system and a simple and rapid method for antioxidant activity evaluation was developed. To avoid the time consuming step of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) radical cation preparation by chemical oxidation of ABTS, as in the original TAEC assay, and hence, to shorten the analysis time, the ABTS radical cation was generated on-line by electrochemical oxidation of ABTS in the flow-through electrolysis cell forming a part of the FIA system. The proposed method was optimised with respect to a flow rate, injection volume and ABTS radical cation/carrier ratio. Under the optimised conditions linear calibration graphs for Trolox were obtained over the range 10-100 microM, with a limit of detection 1.6 microM. Good reproducibility (relative standard deviation 1.95%) and sample throughput (32 samples per hour) were achieved. The developed method was applied to the evaluation of the antioxidant activity of pure compounds and samples of some common beverages. In both cases a good correlation between the results obtained by the proposed method and TEAC values evaluated by the classic TAEC decolourisation assay was obtained (r(2)= 0.996 for pure compounds and r(2)= 0.957 for beverage samples).     

Multimodal metal cation sensing with bis(macrocyclic) dye

The synthesis, electrochemical, optical, and cation sensing properties of a bis(macrocyclic) dye 1, in which the benzo-15-crown-5 and phenylazathia-15-crown-5 subunits are linked through a styryl pyridinium moiety, are reported. In this new ditopic receptor, the benzo-15-crown-5 macrocycle acts as a highly selective binding site for alkaline earth metal cations (Mg(II) and Ba(II)), whereas the phenylazathia-15-crown-5 displays a strong binding affinity towards soft heavy-metal cations (Hg(II) and Ag(I)). The pronounced changes of the absorption and fluorescence spectra of this bichromophoric dye observed upon different metal cation addition make the dye suitable for dual-wavelength analysis and offer an enticing potential for multitasking sensors.     

Synthesis of photochromic diarylethenes using a microflow system

An effective method for the synthesis of photochromic diarylethenes based on microflow systems has been developed, and the synthesis of unsymmetrical diarylethenes which is difficult to achieve using conventional macro batch systems, has been accomplished.     

组合电化学--电化学研究中的新策略

组合电化学是一种新的电化学研究策略，通过设计和构建大量多样性的电极阵列，并对其进行高通量筛选和表征，快速、高效地实现了体系的电化学研究。本文综述了近年来进行的组合电化学研究，重点介绍了组合光学筛选方法、组合电化学合成方法以及电化学平行筛选方法，并探讨了各种方法的优势和存在的问题。     

Facial selectivity of the (R)-1,3-dimethyl-1-cyclohexyl cation in the gas phase

The model reaction between the (R)-1,3-dimethyl-1-cyclohexyl cation (I) and methanol has been investigated under gas-phase radiolytic conditions (750 Torr; 25-120 degrees C) with the aim of evaluating the intrinsic factors that govern the facial selectivity of biased carbocations. The peculiarity of the experimental approach allows the formation of different CH(3) (18)OH.I ionic adducts. Subsequent conversion of these adducts to give the corresponding E/Z covalent products follows different reaction coordinates, which are characterized by their own activation parameters. On the grounds of density functional theory (DFT) results, several [CH(3)OH.I] structures have been located on the relevant potential-energy surface (PES). The experimental results point to a gas-phase facial selectivity, which is mainly governed by entropic factors that arise as a result of the occurrence of different noncovalent ion-molecule "facial adducts" (FA). The formation of FAs may also play an important role in both the reaction dynamics and the positional selectivity. The present results cannot be interpreted by any of the models based on solution-phase experiments.     

Bicyclo[3.2.1]octa-3,6-dien-2-yl cation: a bishomoantiaromate

Antiaromatic compounds with a closed loop of 4n p-electrons are relatively unstable and often difficult to study. We report in this article the synthesis of alcohols 2-(4'-fluorophenyl)bicyclo[3.2.1]octan-2-ol 11, 2-(4'-fluorophenyl)bicyclo[3.2.1]oct-3-en-2-ol 12, and 2-(4'-fluorophenyl)bicyclo[3.2.1]octa-3,6-dien-2-ol 13 and their transformations into corresponding carbocations 14-16, respectively, in a superacidic medium (FSO3H/SO2ClF) at -120 degrees C. Cations 14-16 are characterized by NMR analysis (1H, 13C, 19F), and 15 and 16 are further characterized by quenching in NaOCH3/H3COH at -120 degrees C. The relative stabilities of 14-16 are determined experimentally by 19F NMR spectroscopy. Cation 16 is found to be experimentally less stable than cation 15 by 3.7 kcal/mol. DFT calculations (structure and energy: B3LYP/6-31G(d); NMR: B3LYP/6-311+G(2d,p)) are performed for alcohols 11-13 and bicyclo[3.2.1]octyl cations 6, 7, 9, 14-16, 26, 28, and 30. In the case of 11-16, data from DFT calculations is in good agreement with experimental data. Because 6,7-dimethylenebicyclo[3.2.1]oct-3-en-2-yl cation 26 is more stable than cation 7 by 1.69 kcal/mol, the inductive effect of sp(2)-hybridized carbon atoms C6 and C7 in carbocations 6 and 16 cannot be the reason for the destabilization of 6 relative to 7 and 16 relative to 15. Destabilization of 6 relative to 7 and 16 relative to 15 and the calculated NICS of 6 (+4.17 ppm) and 16(+3.3 ppm) document that 6 and 16 are bishomoantiaromates.     

Observation of heptamethylbenzenium cation over SAPO-type molecular sieve DNL-6 under real MTO conversion conditions

The heptamethylbenzenium cation (heptaMB(+)) has been speculated to be one of the most important active intermediates involved in the "hydrocarbon pool" mechanism of methanol-to-olefin (MTO) conversion. By the use of DNL-6, a newly synthesized SAPO-type molecular sieve with large cavities, heptaMB(+) has for the first time been directly observed during methanol conversion under real working conditions. (13)C-labeling experiments suggested that olefin formation mediated by heptaMB(+) mainly follows the side-chain mechanism.     

Tetramethylcyclobutadiene radical cation

The tetramethylcyclobutadiene radical cation has been generated photochemically in solutions of aluminum halide σ complexes of tetramethylcyclobutadiene. It decays thermally to a “dimeric” radical cation.     

Microflow electroorganic synthesis without supporting electrolyte

Anodic methoxylation of several organic compounds has been successfully achieved in the absence of intentionally added supporting electrolyte using an electrochemical microflow system.     

Effect of the intercalated cation on the properties of poly(o-methylaniline)/maghnite clay nanocomposites

A detailed study about the synthesis, characterization and properties of poly(o-methylaniline)(PoMea)/maghnite nanocomposites has been performed. Changes in the characteristics of the nanocomposites, depending on the intercalated cation between the clay layers before the synthesis, have been observed. Intercalated morphology has been detected by TEM in nanocomposites containing copper-treated maghnite (Magh-Cu), while when maghnite treated with strong acids was used (Magh-H); an exfoliated material has been obtained. Also, remarkable differences in the properties of the polymers have been observed by TG-MS and FTIR, suggesting that the polymer produced with Magh-H has a higher degree of branching. The electrochemical behavior of the polymers extracted from the nanocomposites has been studied by cyclic voltammetry. Good electrochemical response has been observed for PoMea grown into Magh-Cu but not for the one polymerized into Magh-H.     

Synthesis and cation complexation properties of new macrolides

The cis-2-alkyl-3-oxy-tetrahydropyran unit as a novel structure for the design and synthesis of a new type of ionophores with C₂-symmetry is reported. The synthesis of seven different macrolides and a crown ether and their cation complexation properties were investigated. The X-ray crystal structure of some of the receptors provides valuable information on the preferred conformation of tetrahydropyrans in the solid state that can be related to the cation complexation properties in solution. The kinetic template effect has been proved to be a useful tool to improve the yield and selectivity in the synthesis of macrodiolide 3.     

UV Raman spectrum of 1,3-dimethylcyclopentenyl cation adsorbed in zeolite H-MFI

The first Raman spectrum of an adsorbed carbenium ion has been measured: The 1,3-dimethylcyclopentenyl cation adsorbed in zeolite H-MFI. 1,3-Dimethylcyclopentenyl cation has been observed as a component of the hydrocarbon pool formed during the methanol-to-gasoline process catalyzed by zeolite H-MFI. The Raman shifts recorded for 1,3-dimethylcyclopentenyl cation are in remarkable agreement with computer calculations of the vibrational band positions for the isolated cation. This agreement suggests that the cation is unperturbed by interactions with the zeolite pore walls so that Raman spectra of free or solution-phase hydrocarbons can be used to identify these same species adsorbed in zeolite pores.     

UV-vis and IR spectral characterization of persistent carbenium ions, generated upon incorporation of cinnamyl alcohols in the acid zeolites HZSM-5 and HMor

Cinnamyl alcohol (1) and two derivatives 2 and 3 have been incorporated in dehydrated HMor and HZSM-5 zeolites with the aim to characterize spectroscopically the corresponding carbocations generated within the solids. Product studies of the supernatant liquid phase combined with diffuse reflectance UV-vis and IR spectroscopy provide unequivocal evidence for the carbocations. Thus, cinnamyl alcohol (1) affords the 1,5-diphenylpentadienyl cation in HMor and HZSM-5 as a persistent species. In the case of HMor with larger pore dimensions the bulkier 1-(2'-cinnamyl)-3-phenylpropenyl cation was also spectroscopically detected. No persistent carbocation was observed when the alpha-methylcinnamyl alcohol (2) was incorporated in the acid zeolites, wherein a complete cyclization to 2-methylindene takes place. Finally, incorporation of 2-methyl-4-tolyl-3-buten-2-ol (3) in HZSM-5 allowed detection of the gem-dimethyl-subsituted p-methylcinnamyl cation, with a lifetime of hours. This cation is not persistent enough in HMor to be characterized. The present study illustrates how structurally related allylic substrates may give distinct carbenium ions whose persistence depends on the host-guest fit in the interior of the acid zeolites.