We report herein
a modular class of organic catalysts that, acting
as donors, can readily form photoactive electron donor–acceptor
(EDA) complexes with a variety of radical precursors. Excitation with
visible light generates open-shell intermediates under mild conditions,
including nonstabilized carbon radicals and nitrogen-centered radicals.
The modular nature of the commercially available xanthogenate and
dithiocarbamate anion organocatalysts offers a versatile EDA complex
catalytic platform for developing mechanistically distinct radical
reactions, encompassing redox-neutral and net-reductive processes.
Mechanistic investigations, by means of quantum yield determination,
established that a closed catalytic cycle is operational for all of
the developed radical processes, highlighting the ability of the organic
catalysts to turn over and iteratively drive every catalytic cycle.
We also demonstrate how the catalysts’ stability and the method’s
high functional group tolerance could be advantageous for the direct
radical functionalization of abundant functional groups, including
aliphatic carboxylic acids and amines, and for applications in the
late-stage elaboration of biorelevant compounds and enantioselective
radical catalysis.
Reported herein is av isible-light-mediated radical approach to the a-alkylation of ketones.T his method exploits the ability of anucleophilic organocatalyst to generate radicals upon S N 2-based activation of alkylh alides and blue light irradiation. The resulting open-shell intermediates are then intercepted by weakly nucleophilic silyl enol ethers,w hich would be unable to directly attackt he alkylh alides through at raditional two-electron path. The mild reaction conditions allowed functionalization of the a position of ketones with functional groups that are not compatible with classical anionic strategies.Inaddition, the redox-neutral nature of this process makes it compatible with ac inchona-based primary amine catalyst, whichw as used to develop ar are example of enantioselective organocatalytic radical a-alkylation of ketones.
Radical cross-coupling reactions represent a revolutionary tool to make C(sp3)–C and C(sp3)–heteroatom bonds by means of transition metals and photoredox or electrochemical approaches. However, the use of main-group elements to harness this type of reactivity has been little explored. Here we show how a low-valency bismuth complex is able to undergo one-electron oxidative addition with redox-active alkyl-radical precursors, mimicking the behaviour of first-row transition metals. This reactivity paradigm for bismuth gives rise to well-defined oxidative addition complexes, which could be fully characterized in solution and in the solid state. The resulting Bi(III)–C(sp3) intermediates display divergent reactivity patterns depending on the α-substituents of the alkyl fragment. Mechanistic investigations of this reactivity led to the development of a bismuth-catalysed C(sp3)–N cross-coupling reaction that operates under mild conditions and accommodates synthetically relevant NH-heterocycles as coupling partners.
The bonding mode
of carbon dioxide with the surface of various
forms of MgO has been investigated by means of density functional
theory calculations. Four supports have been considered: the bare
MgO(100) surface, the surface of Al-doped MgO, and ultrathin MgO/Ag(100)
and MgO/Mo(100) films. Three forms of adsorbed CO2 have
been investigated: physisorbed CO2, chemisorbed carboxylate,
CO2
–, and carbonate, CO3
2–. While on MgO(100) CO2 forms either the
physisorbed species or the more stable surface carbonate, on Al-doped
MgO carboxylate is the preferred species. The adsorption properties
of one- or two-layer MgO films differ completely as a function of
the metal support. On MgO/Ag(100) the properties of adsorbed CO2 are very similar to those of the MgO(100) surface (formation
of carbonate, not of carboxylate); on MgO/Mo(100), on the contrary,
both carbonate and carboxylate species can form, depending on the
film thickness. On a one-layer film, both species are formed with
a comparable stability, while for thicker films the carboxylate species
becomes unstable. The surface of Al-doped MgO(100) exhibits similar
features to that of the nondefective MgO/Mo(100) one-layer film.
We report a photocatalytic strategy for the chemodivergent radical benzylation of 4-cyanopyridines. The chemistry uses a single photoredox catalyst to generate benzyl radicals upon N-F bond activation of 2-alkyl N-fluorobenzamides....
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