Ring-Closure Reactions of ortho-Vinyl-tert-anilines and (Di)Aza-Heterocyclic Analogues via the tert-Amino Effect: Recent Developments

One version of the tert-amino effect operating in tert-anilines possessing an ortho-vinyl substituent affords a fused tetrahydropyridine ring by an isomerization process with the formation of a new carbon-carbon bond between the vinyl and tert-amino moieties. Since its discovery in 1984, this type of cyclization has been efficiently used for the construction of fused-ring systems. However, it has been found that the electron-deficient heterocyclic analogues of tert-anilines, such as diazines, may undergo isomerization at considerably lower reaction rates and, as a consequence, their reactions may require harsh conditions. Recent synthetic studies have indicated that the rate and yield may be improved by incorporating the β-vinylic carbon atom into an electron-deficient ring and/or buttressing the tert-amino group, and/or performing the reaction by means of microwave irradiation.