E. coli cells containing overexpressed (R)-selective ω-transaminase and the cofactor PLP were immobilized on methacrylate beads suitable for continuous flow applications. The use of an organic solvent suppresses leaching of PLP from the cells; no additional cofactor was required after setting up the packed-bed reactor containing the biocatalyst (ω-TA-PLP). Non-natural ketone substrates were transformed in flow with excellent enantioselectivity (99%ee). Features of this novel system include high-throughput (30−60 min residence time), clean production (no quench, workup, or purification required), high enzyme stability (the packedbed reactor can be continuously operated for 1−10 days), and excellent mass recovery.
Small molecules bearing 1,2,3-triazole functionalities are important intermediates and pharmaceuticals. Common methods to access the triazole moiety generally require the generation and isolation of organic azide intermediates. Continuous flow synthesis provides the opportunity to synthesize and consume the energetic organoazides, without accumulation thereof. In this report, we described a continuous synthesis of the antiseizure medication rufinamide. This route is convergent and features copper tubing reactor-catalyzed cycloaddition reaction. Each of the three chemical steps enjoys significant benefits and has several advantages by being conducted in flow. The total average residence time of the synthesis is approximately 11 min, and rufinamide is obtained in 92% overall yield
Phenols are important compounds in chemical industry. An economical and green approach to phenol preparation by the direct oxidation of aryl Grignard reagents using compressed air in continuous gas-liquid segmented flow systems is described. The process tolerates a broad range of functional groups, including oxidation-sensitive functionalities such as alkenes, amines, and thioethers. By integrating a benzyne-mediated in-line generation of arylmagnesium intermediates with the aerobic oxidation, a facile three-step, one-flow process, capable of preparing 2-functionalized phenols in a modular fashion, is established.
A mechanism-guided design of a multi-step flow system enabled an efficient general process for the synthesis of cyclic carbonates from alkenes and CO2. The flow system proved to be an ideal platform for multicomponent reactions because it was straightforward to introduce reagents at specific stages without their interacting with each other or with reaction intermediates prone to destruction by them. This system exhibited superior reactivity, increased yield, and broader substrate scope relative to conventional batch conditions and suppressed the formation of undesired byproducts, such as, epoxides and 1,2-dibromoalkanes.
A continuous end-to-end synthesis and purification of diphenhydramine hydrochloride featuring atom economy and waste minimization is described. Combining a 1 : 1 molar ratio of the two starting material streams (chlorodiphenylmethane and N,N-dimethylaminoethanol) in the absence of additional solvent at high temperature gives the target compound directly as a molten salt (ionic liquid above 168 °C) in high yield.
Go with the flow: A general approach for amide bond formation by way of a continuous-flow photochemical rearrangement of nitrones was described (see scheme). Simple aryl-alkyl amide bonds as well as complex peptide bonds were constructed efficiently with a residence time less than 20 minutes. A tetrapeptide was synthesized in this way and the method could be applied to peptide fragment coupling.
The first continuous hydrogenation that requires neither H2 nor metal catalysis generates diimide by a novel reagent combination. The simple flow reactor employed minimizes residence time by enabling safe operation at elevated temperature.
We report a method for the oxidation of a range of alcohols and aldehydes utilizing a simple flow system of alcohols in EtOAc with a stream of 12.5% NaOCl and catalytic Bu4NBr. Secondary alcohols are oxidized to ketones, aldehydes are oxidized directly to methyl esters in the presence of methanol, and benzylic alcohols are oxidized to either benzaldehydes or methyl esters, depending on the conditions used. The reaction conditions are mild and generally provide complete conversion in 5–30 min.
A general, green, and efficient Brønsted acid-catalyzed glycosylation serves as a key step in the one-flow, multistep syntheses of several important 5′-deoxyribonucleoside pharmaceuticals.
The preparation of CpRu(MeCN)3PF6 using an easily assembled continuous flow reactor is described. This scalable, reproducible method provides the title compound in excellent yield and purity, and eliminates the need for any purification steps. Under our optimized conditions, the residence time required for complete conversion was only 5 min at an initial substrate concentration of 0.06 M, as compared to a reaction time of 12–36 h for the batch process at 0.02 M. This threefold increase in concentration and significant decrease in reaction time increases the throughput and efficiency of the synthesis. Using the simple laboratory equipment described herein, ruthenium catalyst of 99% purity was produced with a throughput of 1.56 g/h (5 mL reactor), which is 10 times the highest reported throughput for the batch process.