Continuous-flow asymmetric

Fig. 4 Setup for continuous-flow asymmetric hydrovinylation using an IL/SCCO2 biphasic system. Liquid and gaseous substrates are mixed with the SCCO2 stream before entering the tubular reactor unit and bubbled through the catalyst-containing IL using a capillary. The CO2 flow leaves the reactor on top and the product is collected in a cold trap after controlled expansion to ambient pressure...

Scheme 7.23 Continuous-flow asymmetric cyanation of imines using self-supported complex 30.

Soloshonok, V.A., Catt, H.T., and Ono, T. (2009) Continuous-flow asymmetric biomimetic transamination. 

Figure 3.3. Asymmetric hydroformylation of non-volatile substrates using a stepwise injection into continuous flow reactor with scCC>2 as mobile phase...

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

With numerous researchers investigating the advantages associated with thermally or biocatalytically controlled asymmetric syntheses, some of which have been performed in continuous flow reactors, few have considered the prospects of photochemical asymmetric synthesis, an idea... 

The major advantage of the use of CuHY as a catalyst for this reaction is the ease with which it can be recovered from the reaction mixture by simple filtration if used in. a batch reactor (alternatively it can be used in a continuous flow fixed bed reactor). We have carried out the heterogeneous asymmetric aziridination of styrene until completion, filtered and washed the zeolite then added fresh styrene, PhI=NTs and solvent, without further addition of chiral bis(oxazoline), for several consecutive experiments. The yield and the enantioselectivity decline slightly on reuse we have found that adsorbed water can build up within the pores of the zeolite on continued use and we believe that this is the cause of loss of activity and enantioselection. However, full enantioselectivity and yield can be recovered if the catalyst is simply dried in air prior to reuse, or alternatively the catalyst can be recalcined and fresh oxazoline ligand added. 

Figure 4. The nickel catalyst for asymmetric hydrovinylation (see eq. (6)) is activated, tuned, and immobilized in an IL/CO2 continuous-flow system.

A soluble polymer-bound version of the asymmetric dihydroxylation ligand is provided by DHQD-PHAL-OPEG-OMe, a polyethylene glycol derivative [152, 153]. The use of a PEG system with a ligand at each end allowed the dihydroxylation reaction to be run in a continuous flow system with a membrane to retain the ligand. Under these conditions, metal leaching was observed [154]. 

A continuous-flow method for asymmetric catalysis in an SCF/IL system was reported by Leitner s group (144), with the hydrovinylation of styrene [Eq. (31)] as the test reaction. The SCCO2 solution of styrene and ethylene was continuously bubbled up through a column of ionic liquid containing the catalyst. The enantio selectivity was found to be high (in one of the ILs) and catalyst stability was enhanced due to the fact that there was a constant concentration of substrate in the system the catalyst was unstable in ILs in the absence of the olefins. 

Several enantioselective reductions that use polymer-supported chiral catalysts have been reported. A maj or advantage of performing enantioselective reactions with polymer-supported catalysts is that their use allows both the recycHng of the catalysts and the easy separation of the low molecular weight chiral products. One of the most attractive methods to carry out asymmetric synthesis is the continuous flow system by using an insoluble, polymeric catalyst. 

With numerous researchers investigating the advantages associated with the thermal or biocatalytic control of asymmetric reactions, Ichimura and co-workers [89] considered the potential of photochemical asymmetric syntheses performed in continuous flow reactors. To investigate the hypothesis, the authors employed the asymmetric photochemical addition of MeOH to (R)-( + )-(Z)-limonene (159) as a model reaction, comparing three quartz micro reactors, with a standard laboratory cell as a means of highlighting the synthetic potential of this approach. 

In this context, however, asymmetric transformations with chiral metal complexes or enzymes are particularly important. The demand for enantiopure building blocks in the fine chemical and pharmaceutical industries is still hampered by simple asymmetric processes which can be scaled up, as well as by the stability, recyclability, and hence the price of most chiral catalysts (refer also to the chapter by K.-U. Schoning in this volume). Immobilization of effective and robust catalytic systems and their application in continuous flow reactors is regarded as a key for success in this field. 

This example illustratively shows that inorganic materials are well suited for continuous flow processes in column-like reactors. Thus, covalently immobilized NH-benzyl-(li, 2S)-(-)-norephedrine 10 on silica inside a column was doped with ruthenium. This setup was used to carry out continuous asymmetric transfer hydrogenation reactions (Scheme 10) [38]. Remarkably,no catalyst deactivation occurred over a period of one week, which the authors ascribed to the successful site isolation of the catalyst on the support. 

James is also an active postdoctoral researcher. His research interests centre on clean synthesis with focus on asymmetric induction in enantiose-lective catalysis, utilization of CO and CO2 as a sustainable source of chemicals, heterogeneous catalysis and novel reaction technologies including cold plasma reactors and continuous flow synthesis. 

As in gas-liquid systems, this flow is formed based on the type of microchannel geometry used flow symmetric geometry forms annular flow, while flow asymmetric forms parallel flow. This flow regime is observed at elevated flow rates in the microchannel without static internals - the higher the flow velocity, the better the stability. The shear force of the continuous phase is dominant over the surface tension force and, therefore, the dispersed phase flows straight forming annular or parallel flow. 

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