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 β-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 β-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 β-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 β-dicarbonyl compound serves as a carbon nucleophile to trap the alkene cation radical in PET reactions to lead to C−C bond formation.