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

ABSTRACT 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. This review describes relatively recent synthetic transformations involving this type of TERT-amino effect and devotes special attention to structure-reactivity relationships including regio- and stereo­chemical aspects. 1 Introduction 2 The TERT-Amino Effect: Type 2 Reactions 2.1 Substrates with a Dicyanovinyl Group 2.1.1 Benzene Derivatives 2.1.2 Pyridine Derivatives 2.1.3 Pyrimidine Derivatives 2.1.4 Pyridazine Derivatives 2.2 Substrates with a Cyclic Vinyl Substituent 2.2.1 Pyridazine Derivatives 2.2.2 Pyrimidine Derivatives 2.2.3 Benzene Derivatives 2.3 Microwave-Assisted Synthesis 2.4 Regio- and Stereochemical Features 3 Conclusions