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Copper mediated cyclization of 1-substituted enamides, dienamides and trienamides: regiochemistry, indigoid formation and methyl migration-aromatization
- Geden, Joanna V., Clark, Andrew J., Coles, Stuart R., Guy, Collette S., Ghelfi, Franco, Thom, Stephen
- Tetrahedron letters 2016 v.57 pp. 3109-3112
- beta-ionone, chemical structure, dimerization, hydrochloric acid
- Copper mediated cyclization of activated 1-substituted enamides occurs via a 5-endo radical-polar crossover process. Trichloroacetyl derivatives can undergo further reactions post cyclization (elimination of HCl or dimerization potentially via copper carbenoid intermediates). Reaction of α-halo trienamides derived from β-ionone furnish either β- or γ-lactams via 4-exo or 5-exo cyclizations respectively depending upon the enamide tautomer undergoing reaction. For the less reactive dichloroacetamide derivative a competing regioselective methyl migration-aromatization prior to cyclization is observed.