Synthesis of 1,3-diazaazulene derivatives of colchicinoids and isocolchicinoids via ipso- or tele-substitution-condensation with amidines

Article abstract of DOI:10.1016/S0040-4020(98)00856-4

Condensation of colchicinoids and isocolchicinoids with amidines in dry benzene affords regioselectively 1,3-diazaazulene derivatives: ipso- substitution-condensation products (e.g. 7) are best obtained from cycloheptatrienone-ring deactivated substrates (e.g. 4), whereas isomeric tele-substitution-condensation products (e.g. 13), are best accessible from cycloheptatrienone-ring activated substrates (e.g. 10). Hydroxylic solvents inhibit tele-substitution-condensation, arguably by undergoing protonation in preference of the intermediate σ adduct.