Photoinduced three-component reactions of tetracyanobenzene with alkenes in the presence of 1,3-dicarbonyl compounds as nucleophiles.

Photoinduced three-component reactions between tetracyanobenzene (TCNB), an aromatic olefin, and a /3-dicarbonyl compound afford products composed of the three components via formal elimination of hydrogen cyanide, leading to the vicinal dialkylation of the olefin and the α-alkylation of the /?-dicarbonyl compounds. It is shown that these reactions are initiated by photoinduced electron transfer (PET) from the olefin to the singlet excited TCNB and proceed by a nucleophile-olefin combination, aromatic substitution (NOCAS) reaction sequence with the enolized /3-dicarbonyl compound as a nucleophile. Therefore, aromatic olefins are suitable substrates in photo-NOCAS reactions when TCNB is used as the electron acceptor. In addition, these results show that the enol of /?-dicarbonyl compound serves as a carbon nucleophile to trap the alkene cation radical in PET reactions to lead to C-C bond formation.