Blue light mediated C–H arylation of heteroarenes using TiO₂as an immobilized photocatalyst in a continuous-flow microreactor

Abstract

Improved contacting of TiO2 catalyst, substrate and light results in an impressive boost in reactor performance for blue light mediated C–H arylation of heteroarenes in continuous-flow mode.

Visible‐Light‐Induced, Catalyst‐Free Radical Arylations of Arenes and Heteroarenes with Aryldiazonium Salts

“…Such photocatalyzed reactions can be conducted with a number of aryl radical precursors including diazonium and iodonium salts, diazoanhydrides, carboxylic acids, azo sulfones, and iodo‐, bromo‐, and chloroarenes . Typically employed photocatalysts are complexes of ruthenium or iridium, eosin Y, titanium dioxide,, or strong electron donors, and double excitation of perylene bisimide recently allowed the conversion of aryl chlorides …”

Flow Photochemistry: Shine Some Light on Those Tubes!

“…Another interesting example of gas-liquid reaction under segmented Stern-Volmer analysis: while fluorescence-quenching tests are used to determine whether a substrate or reagent is able to quench a photoredox catalysts (i.e., able to be oxidized or reduced), Stern-Volmer measurements provide quantitative information about the quenching. [28,31,33]; (B) tube-in-tube reactor for gas-liquid reactions [38]; (C) falling-film (micro)reactor [41]; (D) packed-bed reactor [47,48]; and (E) segmented flow for solid-liquid reactions [53]. flow conditions is the synthesis of the antimalarial drug artemisinin via photogenerated singlet oxygen oxidation directly from extracts of the plant Artemisia annua, containing both the precursor of this drug [dihydroartemisinic acid (DHAA)] and the chlorophyll photocatalyst, demonstrated by Gilmore [33].…”

“…These reactors are, interestingly, also suitable for heterogeneous catalysis. An interesting example was reported by Rehm and Rueping, who studied a TiO 2 -catalyzed photochemical coupling between diazoarenes and heterocycles operating under blue-light irradiation [41]. The reactor walls were coated with the solid catalyst, with an inert (rather than reactive) gas flowing counter current.…”

Mechanochemistry for “no solvent, no base” preparation of hydantoin-based active pharmaceutical ingredients: nitrofurantoin and dantrolene

“…In the case of dantrolene, the condensation reaction leading to the hydrazone occurs in the presence of 5-(4-nitrophenyl)-2-furfural, in similar reaction conditions (DMF/HCl 35% 20 or in acetonitrile 21 at room temperature up to 8 hours), with yields in the range 41-96% after purification by precipitation in hexane 22 or water, 20,[23][24] or by colum chromatography. 21 To our surprise, despite the simplicity of the preparation of arylhydrazones in solventfree conditions by mechanochemistry, grinding in a mortar 25 or ball-milling (vibrating [26][27][28][29] or planetary [30][31][32] ) from aryl diazonium salts in the presence of active methylene compounds 29 or more likely, by a condensation reaction, 25,[27][28][30][31] those methodologies were never applied to the preparation of nitrofurantoin 7 or dantrolene 8.…”