368-71-8Relevant articles and documents
Photocatalytic Oxidative [2+2] Cycloelimination Reactions with Flavinium Salts: Mechanistic Study and Influence of the Catalyst Structure
Hartman, Tomá?,Reisnerová, Martina,Chudoba, Josef,Svobodová, Eva,Archipowa, Nataliya,Kutta, Roger Jan,Cibulka, Radek
, p. 373 - 386 (2021/02/01)
Flavinium salts are frequently used in organocatalysis but their application in photoredox catalysis has not been systematically investigated to date. We synthesized a series of 5-ethyl-1,3-dimethylalloxazinium salts with different substituents in the positions 7 and 8 and investigated their application in light-dependent oxidative cycloelimination of cyclobutanes. Detailed mechanistic investigations with a coumarin dimer as a model substrate reveal that the reaction preferentially occurs via the triplet-born radical pair after electron transfer from the substrate to the triplet state of an alloxazinium salt. The very photostable 7,8-dimethoxy derivative is a superior catalyst with a sufficiently high oxidation power (E=2.26 V) allowing the conversion of various cyclobutanes (with Eox up to 2.05 V) in high yields. Even compounds such as all-trans dimethyl 3,4-bis(4-methoxyphenyl)cyclobutane-1,2-dicarboxylate can be converted, whose opening requires a high activation energy due to a missing pre-activation caused by bulky adjacent substituents in cis-position.
Mild and selective hydrogenation of nitro compounds using palladium nanoparticles supported on amino-functionalized mesocellular foam
Verho, Oscar,Gustafson, Karl P. J.,Nagendiran, Anuja,Tai, Cheuk-Wai,B?ckvall, Jan-E.
, p. 3153 - 3159 (2015/02/03)
We present the utilization of a heterogeneous catalyst comprised of Pd nanoparticles supported on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF) for the selective hydrogenation of aromatic, aliphatic, and heterocyclic nitro compounds to the corresponding amines. In general, the catalytic protocol exclusively affords the desired amine products in excellent yields within short reaction times with the reactions performed at room temperature under ambient pressure of H2. Moreover, the reported Pd nanocatalyst displayed excellent structural integrity for this transformation as it could be recycled multiple times without any observable loss of activity or leaching of metal. In addition, the Pd nanocatalyst could be easily integrated into a continuous-flow device and used for the hydrogenation of 4-nitroanisole on a 2.5 g scale, where the product p-anisidine was obtained in 95% yield within 2 h with a Pd content of less than 1 ppm.
Synthesis of riboflavines, quinoxalinones and benzodiazepines through chemoselective flow based hydrogenations
Baumann, Marcus,Baxendale, Ian R.,Hornung, Christian H.,Ley, Steven V.,Rojo, Maria Victoria,Roper, Kimberley A.
, p. 9736 - 9759 (2014/08/05)
Robust chemical routes towards valuable bioactive entities such as riboflavines, quinoxalinones and benzodiazepines are described. These make use of modern flow hydrogenation protocols enabling the chemoselective reduction of nitro group containing building blocks in order to rapidly generate the desired amine intermediates in situ. In order to exploit the benefits of continuous processing the individual steps were transformed into a telescoped flow process delivering selected benzodiazepine products on scales of 50 mmol and 120 mmol respectively.
