Photochemically induced symmetrical coupling reactions between cyclohexa-2,4-dienones and α,ω-diamines. A new approach to the selective labelling of peptides and proteins

2,4,6-Trimethylcyclohexa-2,4-dien-1-one derivatives undergo ring cleavage to furnish symmetrical amides on irradiation with visible light in the presence of various α,ω-diamines. Five different symmetrical amides containing a substituted diene moiety were synthesized in 65–85% yield.