Journal of Flow Chemistry最新文献

In this paper we report a [2 + 2] cycloaddition reaction between ketenes and benzils, characterized by an unusual double photochemical activation triggered by visible light. Employment of a flow system and optimization of reaction conditions through Design of Experiments resulted in moderate to good yields of the corresponding β-lactones. A thorough computational analysis allowed to elucidate the mechanism of the reaction and justify the observed diastereoselectivity. The reaction was also successfully tested with mixed benzils, showing complete regioselectivity.

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We investigated the flow acetalization of aldehydes and THP protection of alcohols using sulfonic acid-functionalized silica gel having hydroxy moiety (HO-SAS) as the solid acid catalyst. The reaction both aliphatic and aromatic aldehydes reacted with methanol within 5 min of residence time to give acetalization product in good to excellent yield. THP protection of primary, secondary, and tertiary alcohols proceeded well to the corresponding products. Both reactions did not require a neutralization process. Scalable syntheses were also achieved with continuous operation. The deprotection reactions were also effective using HO-SAS packed flow reactors.

Micro-distillation is one of the unit operation technologies that are looking toward innovation through on-site and on-demand production system. In this study, a simple structure microdistillator consisting of some plates was applied to reactive distillation, and its potential was investigated. As a target reaction, the heterogeneous esterification between acetic acid and methanol using a solid acid catalyst was employed. The effects of feedstock supply rate, feedstock composition, and device temperature on operation stability and conversion were examined. By controlling the feedstock supply rate and temperature properly, a stable operation with a conversion of approximately 100% was successfully achieved. The amount of methyl acetate produced per weight of catalyst was greater in the reactive distillation using a microdistillator than in the batch reaction, soon after the start of the reaction. Thus, it was demonstrated that the reactive distillation using a microdistillator was able to achieve highly efficient reactions with short reaction time and small amounts of catalyst.

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A vicinal diamine motif can be found in numerous natural compounds and pharmaceuticals, making it an important synthetic target. Herein, we report a telescoped synthesis of vicinal diamines under continuous flow conditions. This approach involves the electrochemical aziridination of alkenes with primary amines, followed by the strain-release driven ring-opening using various nitrogen nucleophiles. The efficacy of the developed method was demonstrated through the synthesis of diverse symmetrically and non-symmetrically substituted vicinal diamines, as well as vicinal amino azides, which can be further hydrogenated to diamines in flow. Additionally, O-centered nucleophiles were employed for the ring-opening of aziridines in our telescoped synthesis, yielding vicinal amino ethers and alcohol. This process offers a streamlined and efficient pathway for the direct synthesis of valuable products from readily available starting materials, bypassing the isolation of unstable aziridine intermediates.

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The recent advances in the area of electrophotocatalysis (EPC) show that it is a highly suitable technique to yield greener and more sustainable organic synthesis. The overall productivity of EPC however is constrained by a multitude of practical limitations, which impose difficulties in effectively harmonizing the photochemical and electrochemical steps, let alone in accelerating both steps simultaneously. In this contribution, we have tackled these limitations by developing a parallel plate flow cell that permits the execution of EPC in continuous flow. By using a transparent electrode, such as fluorine-doped tin oxide (FTO) or indium tin oxide (ITO) coated glass, the interelectrode distance could be reduced while improving photon absorption. By enhancing both the photochemical and electrochemical steps simultaneously, a notable increase in productivity and space–time-yield (a ten-fold and 300-fold improvement, respectively) of the N-arylation of different azoles was observed. In addition, this was achieved in a single-pass process under electrolyte-free conditions.

An explorative study on the continuous flow generation of the N-F reagent 2,6-dichloro-1-fluoro-pyridinium tetrafluoroborate from 2-6-dichloropyridine and 10% F₂/N₂ and its telescoped downstream electrophilic fluorination reaction with an enamine is reported. The 2-step procedure was performed in a modular lab-scale silicon carbide flow reactor, which safely allowed processing corrosive F₂ and precise temperature control. Both reaction sequences turned out to be very fast when carried out in flow at − 10 °C: the N-F generation step could be done within 7.9 s and only 6.6 s were necessary for the fluorination of the enamine.

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We are currently experiencing a resurgence in the realm of electrochemical organic synthesis, driven by the transformative potential of conducting redox chemistry under mild conditions through the simple use of electrons, thereby circumventing the use of harmful reductants and oxidants. This renaissance is further bolstered by the fusion of electrochemistry with flow chemistry, which not only grants precise control over reaction parameters but also promotes sustainability and heightened reproducibility. Despite these promising advancements, the application of flow electrochemistry to steer asymmetric processes remains in its nascent stage. This perspective delves into the limited contributions to date, shedding light on critical challenges and presenting prospective solutions that are essential for fully unleashing the untapped potential of this field.

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Reactive organometallic intermediates present a distinct opportunity for the creation of novel carbon-carbon and carbon-heteroatom bonds. Whereas their utility in synthesis is well-established, the thermal sensitivity of these species often imposes the requirement for stringent reaction conditions, including strict control of reaction temperatures, concentrations, and use of additives. Moreover, their strong reactivity can pose challenges in achieving the desired selectivity. Since pioneering works in the 2000s, the advent of flow microreactor technology has revolutionized this field, expanding the possibilities of reactive organometallic intermediates within synthetic chemistry. In this review, we provide an overview of the recent advancements in this dynamic area, focusing on breakthroughs that have emerged within the past four years.

In a continuous flow microreactor system, a continuous nitration process of 2-(2,4-dichloro-5-nitrophenyl)-4-(difluoromethyl)-5-methyl-1,2,4-triazol-3-one which is the key intermediate for the synthesis of important triazolinone herbicide Sulfentrazone was developed. The effects of molar ratio of mixed acids, molar ratio of nitric acid to substrate, reaction temperature, total flow rate and residence time in the microreactor on nitration reaction were studied. The results showed that when the flow rate of the material was 60 mL/min, the molar ratio of nitrate to sulfur mixed acid was 1:6, the molar ratio of nitric acid to raw material was 1.1:1, the reaction temperature was 60 ℃, and the residence time was 30 s, the product can be obtained in 97% yield. Compared with the results of nitration process using traditional batch reactors, the use of continuous flow microreactors improved reaction efficiency and achieved higher yields. A characterization kinetics study was conducted on this reaction, and the pre-exponential-factor and activation energy for 2-(2,4-dichlorophenyl)-4-(difluoromethyl)-5-methyl-1,2,4-triazol-3-one nitration were obtained. The activation energy of the reaction is 40.204 kJ/mol. The continuous flow microreactor system greatly increased liquid-liquid two phases mass transfer efficiency, while accurately controlling the reaction temperature and residence time in the reactor.