Expanding the Scope of C-Glycoside Synthesis from Unstable Organolithium Reagents Using Flow Microreactors

C-glycosides are versatile scaffolds for drugs and bioactive compounds. The common organolithium-based synthesis of C-glycosides is limited by low reaction temperatures and a restricted substrate scope. To address these issues, a flow microreactor (FMR) was utilized for rapid mixing and precise temperature control, enabling C-glycoside synthesis at temperatures up to 40 °C and expanding the substrate scope. Continuous C-glycoside synthesis was achieved with a throughput of 21.9 g h-1, demonstrating the industrial potential of FMRs.

Ultrafast Flow Synthesis of o-Functionalized Benzenesulfonyl Fluorides and Subsequent SuFEx Connections via Lithiated Chemistry

Herein we present a flow-based, rapid, and straightforward approach to synthesize diverse functionalized sulfonyl fluorides by harnessing an aryllithium intermediate. The aryllithium intermediate was fully utilized under optimized conditions (0.016 s, -18 °C) to afford various functionalized sulfonyl fluorides and also intramolecular SuFEx cyclization products in high yields (27-94%). Furthermore, the integrated synthesis incorporating subsequent SuFEx connections with even unstable organolithium nucleophiles facilitated one-flow molecular assembly in high yields (42-72%).

Flash chemistry enables high productivity metalation-substitution of 5-alkyltetrazoles

Tetrazoles play a prominent role in medicinal chemistry due to their role as carboxylate bioisosteres but have largely been overlooked as C-H functionalisation substrates. We herein report the development of a high-yielding and general procedure for the heterobenzylic C-H functionalisation of 5-alkyltetrazoles in up to 97% yield under batch conditions using a metalation/electrophilic trapping strategy. Through the use of thermal imaging to identify potentially unsafe exotherms, a continuous flow procedure using a flash chemistry strategy has also been developed, allowing products to be accessed in up to 95% yield. This enabled an extremely high productivity rate of 141 g h-1 to be achieved on an entry-level flow system.

Regioselective Synthesis of α-Functional Stilbenes via Precise Control of Rapid cis-trans Isomerization in Flow

The rapid cis-trans isomerization of α-anionic stilbene was regioselectively controlled by using flow microreactors, and its reaction with various electrophiles was conducted. The reaction time was precisely controlled within milliseconds to seconds at -50 °C to selectively give the cis- or trans-isomer in high yields. This synthetic method in flow was well-applied to synthesize precursors of commercial drug compound, (E)- and (Z)-tamoxifen with high regioselectivity and productivity.

Continuous flow as an enabling technology: a fast and versatile entry to functionalized glyoxal derivatives

We herein report two complementary strategies employing organolithium chemistry for the synthesis of glyoxal derivatives. Micro-mixer technology allows for the generation of unstable organometallic intermediates and their instantaneous in-line quenching with esters as electrophiles. Selective mono-addition was observed via putative stabilized tetrahedral intermediates. Advantages offered by flow chemistry technologies facilitate direct and efficient access to masked 1,2-dicarbonyl compounds while mitigating undesired by-product formation. These two approaches enable the production of advanced and valuable synthetic building blocks for heterocyclic chemistry with throughputs of grams per minute.

A Synthetic Approach to Dimetalated Arenes Using Flow Microreactors and the Switchable Application to Chemoselective Cross-Coupling Reactions

In spite of their potential utility, the chemistry of dimetalated arenes is still in its infancy because they are extremely difficult to synthesize. We report a novel method of synthesizing arenes bearing a boryl group and a metallic substituent, such as boryl, silyl, stannyl, or zincyl groups, in an integrated flow microreactor based on the generation and reactions of aryllithiums bearing a trialkyl borate moiety. The bimetallic arenes showed a remarkable chemoselectivity in palladium-catalyzed cross-coupling reactions. The selectivity was switched by the selection of the metal species that constitutes the dimetalated arenes as well as appropriate catalysts.

A Novel Approach to Functionalization of Aryl Azides through the Generation and Reaction of Organolithium Species Bearing Masked Azides in Flow Microreactors

A novel straightforward method for aryl azides having functional groups based on generation and reactions of aryllithiums bearing a triazene group from polybromoarenes using flow microreactor systems was achieved. The present approach will serve as a powerful method in organolithium chemistry and open a new possibility in the synthesis of polyfunctional organic azides.

Anionic Polymerization Using Flow Microreactors

Flow microreactors are expected to make a revolutionary change in chemical synthesis involving various fields of polymer synthesis. In fact, extensive flow microreactor studies have opened up new possibilities in polymer chemistry including cationic polymerization, anionic polymerization, radical polymerization, coordination polymerization, polycondensation and ring-opening polymerization. This review provides an overview of flow microreactors in anionic polymerization and their various applications.

Suzuki–Miyaura Coupling Using Monolithic Pd Reactors and Scaling-Up by Series Connection of the Reactors

The space integration of the lithiation of aryl halides, the borylation of aryllithiums, and Suzuki–Miyaura coupling using a Pd catalyst supported by a polymer monolith flow reactor without using an intentionally added base was achieved. To scale up the process, a series connection of the monolith Pd reactor was examined. To suppress the increase in the pressure drop caused by the series connection, a monolith reactor having larger pore sizes was developed by varying the temperature of the monolith preparation. The monolithic Pd reactor having larger pore sizes enabled Suzuki–Miyaura coupling at a higher flow rate because of a lower pressure drop and, therefore, an increase in productivity. The present study indicates that series connection of the reactors with a higher flow rate serves as a good method for increasing the productivity without decreasing the yields.

Micromixing enables chemoselective reactions of difunctional electrophiles with functional aryllithiums

Generation of highly unstable functional aryllithiums followed by chemoselective reactions with difunctional electrophiles were successfully achieved using flow microreactor systems equipped with micromixers to give highly functionalized compounds without protecting functional groups.

Integration of borylation of aryllithiums and Suzuki–Miyaura coupling using monolithic Pd catalyst

Integration of the preparation of arylboronic esters and Suzuki–Miyaura coupling using monolithic Pd catalyst was successfully achieved.

A direct and sustainable synthesis of tertiary butyl esters enabled by flow microreactors

A straightforward synthesis of tertiary butyl esters enabled by flow microreactors is reported.

Switching between intermolecular and intramolecular reactions using flow microreactors: lithiation of 2-bromo-2′-silylbiphenyls

Switching between the intermolecular reaction and the intramolecular reaction was achieved at will using flow microreactors.

Flash chemistry: flow chemistry that cannot be done in batch

Flash chemistry based on high-resolution reaction time control using flow microreactors enables chemical reactions that cannot be done in batch and serves as a powerful tool for laboratory synthesis of organic compounds and for production in chemical and pharmaceutical industries.

Novel process windows for enabling, accelerating, and uplifting flow chemistry

Novel Process Windows make use of process conditions that are far from conventional practices. This involves the use of high temperatures, high pressures, high concentrations (solvent-free), new chemical transformations, explosive conditions, and process simplification and integration to boost synthetic chemistry on both the laboratory and production scale. Such harsh reaction conditions can be safely reached in microstructured reactors due to their excellent transport intensification properties. This Review discusses the different routes towards Novel Process Windows and provides several examples for each route grouped into different classes of chemical and process-design intensification.