A metal‐free, visible light‐induced [4+2] benzannulation of biaryldiazonium salts with alkynes was developed. With eosin Y as photoredox catalyst, a variety of 9‐substituted or 9,10‐disubstituted phenanthrenes were obtained via a cascade radical addition and cyclization sequence.
A blue light-promoted cross-coupling of two distinct diazo compounds was described. The reaction produces E-configured trisubstituted alkenes in good yields in the absence of catalysts and additives. The reactive free carbene intermediates were generated via selective photolysis of one of the two diazo compounds upon blue light irradiation.
A photocatalytic decarboxylative/defluorinative reaction of α-trifluoromethyl alkenes with α-keto acids and α-amino acids has been developed. The reaction occurs at room temperature under visible light irradiation, affording various γ,γ-difluoroallylic ketones and 1,1-difluorohomoallyl amines in good yields. The synthetic applications of the resulting functionalized gem-difluoroalkenes were also described.
A mild and efficient method for the synthesis of 6-(trifluoromethyl)phenanthridines through oxidative cyclization of 2-isocyanobiphenyls with CF3SiMe3 under metal-free conditions was developed. The reaction allows the direct formation of C-CF3 bonds and rapid access to phenanthridine ring systems in one catalytic cycle.
A visible-light photoredox synthesis of 3-acylindoles through intramolecular oxidative cyclization of o-alkynylated N,N-dialkylamines is developed. The reaction proceeds effectively under mild reaction conditions using air as the oxidant, and only water is generated as a side product. A plausible mechanism involving the addition of α-amino alkyl radicals to alkynes, followed by C-O bond formation, is proposed.
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