The stable radical cation of large aromatic hydrocarbons remains a challenge, due to the recessive aromatic character and high reactivity. Here we report the design, synthesis, and characterization of new aromatic π-radical cations from one π-electron oxidation of baytwisted dibenzoperopyrene derivatives. Experimental observations and theoretical calculations revealed that these π-radical cations had significant resonance hybrid structures, advantageous to the spin-and charge-delocalizations over the molecular backbones and emerging global aromaticity in the distorted π-system. Therefore, they are thermodynamically stable even without fully steric protection of all C−H bonds on the carbon skeleton and can be well characterized and studied routinely at ambient conditions. Moreover, the π-radical cation materials demonstrated readily formed magnetic molecule aggregates in the solution phase, while in powder states cationic monoradical characters were manifested and in the crystalline state intermolecular through-space interactions were popular. The phenomenon of varied magnetic activity in different states is experimentally investigated by various spectral means and X-ray crystallographic analysis, assisted by DFT calculations. Our study provides an insight into the resonance hybrid effects in the design of stable large aromatic hydrocarbon radical cations and demonstrates state-associated magnetic activities for π-radical cations, which are necessary in applications as magnetic materials.
A visible-light photoredox-catalyzed reductive αaminomethyl carboxylation of styrenes with sodium glycinates and CO 2 has been developed to synthesize a series of α,α-disubstituted γ-amino acids and γ-lactams with high efficiency and regioselectivity. Notably, CO 2 released from the decarboxylation step can be reused for the subsequent carboxylation. Distinct from the previous reactions with the same type of substrates leading to simple decarboxylation and olefin hydroalkylation, this process involves additional CO 2 sequestration, thus leading to olefin α-aminomethyl carboxylation. These findings not only provide new access to α,α-disubstituted γ-amino acids and γ-lactams but also serve as a proof of concept for CO 2 reutilization in decarboxylation reactions.
A visible-light-driven palladium-catalyzed radical oxy-alkylation of 2-(1-arylvinyl)anilines with unactivated alkyl bromides and CO 2 has been developed toward 1,4-dihydro-2H-3,1-benzoxazin-2-ones. This multicomponent reaction (MCR) starts with (1) carboxylation of an amino by CO 2 ; (2) formation of Pd(I) and an alkyl radical via visible-light-driven reaction of alkyl bromides and Pd(0); (3) addition of an alkyl radical to the vinyl followed by single electron transfer (SET) oxidation to the carbocation by Pd(I); and (4) cyclization via intramolecular nucleophilic attack of the carboxylate anion to carbocation.
A photoredox-catalyzed dicarbofunctionalization of styrenes with oxime esters and CO 2 has been achieved. Notably, a series of four-, five-, or six-membered cyclic ketone oximes worked well to furnish a wide range of ε-, ζ-, and η-cyanocarboxylic acids in good yields. Furthermore, a series of γ-keto acids also could be obtained by employing acyclic ketone oxime esters as the carbonyl radical precursor. It provides convergent access to diverse biologically important cyanocarboxylic and γ-keto acids.
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