874-14-6Relevant 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.
Copper-Catalyzed Regioselective Direct C–H Thiolation and Thiocyanation of Uracils
Noikham, Medena,Yotphan, Sirilata
supporting information, p. 2759 - 2766 (2019/04/08)
A novel copper-catalyzed direct C–H thiolation and thiocyanation of uracils using disulfides and thiocyanate salts respectively as coupling partners are described. These reactions enable the C–H bond cleavage and C–S bond formation to proceed efficiently under relatively mild conditions, providing useful methods for a preparation of a series of thio-substituted at the C5 position of uracil derivatives. These protocols exhibit several merits including simple experimental procedures, readily accessible substrates and reagents, broad scopes, high yields, and excellent regioselectivity. Preliminary mechanistic studies revealed that a radical pathway is likely to be involved.
Photocatalytic Systems with Flavinium Salts: From Photolyase Models to Synthetic Tool for Cyclobutane Ring Opening
Hartman, Tomá?,Cibulka, Radek
supporting information, p. 3710 - 3713 (2016/08/16)
Two new photocatalytic systems based on flavinium species formed in situ by protonation of riboflavin-tetraacetate (1) with triflic acid or prepared in advance via alloxazine quaternization are presented as effective tools for oxidative cyclobutane ring [2 + 2] cycloreversion using visible light. The system with 1,3-dimethyl-8-trifluoromethylalloxazinium perchlorate (2c) was found to be superior allowing an acid-free mild procedure, which results in the opening of cyclobutanes with high oxidation potential (up to 2.14 V) and/or with sensitive groups (e.g., furan) without side reactions.
