Visible‐light photoredox catalysis has gained prominence orchestrating challenging chemical transformations under mild reaction conditions. Iridium and ruthenium complexes belong to a prominent group of organometallic photoredox catalysts (PCs) that were employed in light controllable radical polymerization, decarboxylative arylation or acylation, and fluoroalkylation of organic compounds. The rapid establishment of these metal complexes as practical PCs leveraged their well‐studied photophysical and photoredox properties, which in turn have enabled their incorporation in a range of applications.
However, iridium and ruthenium are precious metals and amongst the rarest elements on earth, escalating their costs and presenting concerns related to sustainability and scalability, driving the need to realise new PCs incorporating non‐precious metals or to develop entirely organic replacements.
The application of organic PCs has in particular the following advantages:
i) readily availability,
ii) significantly reduced cost,
iii) prevented contamination of the desired product with toxic heavy metals,
iv) facile property tuning, and
v) low catalyst loading.
The most widely employed organic pigments involve xanthene dyes such as eosin Y, fluorescein, eosin B, and rose bengal but their further structural tuning is limited.
Hence, a development of new and tunable organic substances with perspective photoredox catalytic activity is therefore highly desirable together with the new synthetic routes, yielding high amounts of the PC using less expensive, less toxic, more available, and highly stable reactants.
Technology Features, Specifications and Advantages
The present invention relates to a new straightforward synthetic route to pyrazine-2,3-dicarbonitrile (DCP) derivatives bearing 5-alkoxythiophen-2-yl substituents attached at positions 5 and 6, and their utilisation as catalysts in photoredox reactions.
Despite simple in structure, the DCP derivative possesses properties well-tailored towards photoredox catalysis. Namely, its absorption maxima almost perfectly overlap the white/blue LED emission maxima, a common light source used in photoredox catalysis. With the oxidation/reduction potentials of its excited state within the range of -1.17 to 1.42 V, the DCP catalysts is capable to oxidize/reduce variety of organic substrates.
The main advantages of the invention are:
i) possibility of one-pot synthetic protocol with a short reaction time,
ii) inexpensive and readily available starting materials,
iii) facile purification of the products (e.g. crystallization),
iv) multigram synthesis,
v) very low catalyst loadings (0.01-2 mol%),
vi) high catalytic efficiencies of the catalyst in benchmark CDC reaction with diminished influence of the appended alkyl substituents R,
vii) further application of the catalyst in unprecedented reactions such as chemodivergent reactions with itaconimide, aerobic oxygenation of indoles or enantioselective oxidative olefination of amines.
The novel organic catalyst can be used for photoredox reactions, preferably, the reactions selected from those utilising photoinduced electron transfer or energy transfer. It may facilitate or even allow common/novel laboratory/industrial synthetic processes and also replace organometallic species or xanthene dyes widely used in photoredox processes. It could be used in a range of applications including photovoltaics, therapeutics.
In particular, the novel PC can be applied in the preparation of biologically and medicinally relevant tetrahydroisoquinoline (THIQ) derivatives. THIQ-based analogs exert antiproliferative and antimitotic effects, induce apoptosis and involve autophagic processes. Research in this area will be increasingly performed, especially the investigation into the efficacy of these potential anticancer drugs.
The new synthetic route for the organic PC, yielding high amounts of the PC using less expensive, less toxic, more available, and highly stable reactants. Higly efficient and readily available purely organic PC with manifold possible applications and reasonable price.