New aspects of the chemistry of nonbenzenoid polycyclic conjugated Φ-electron systems

Abstract

Nonbenzenoid polycyclic conjugated Φ-electron systems proved to be exceptional model compounds for testing theoretical predictions and provide interesting information on the relation between electronic structure and physical as well as chemical properties. The continuing need for additional examples of different nonbenzenoid polycyclic Φ-electron systems has stimulated the synthesis of new building blocks as well as the development of new synthetic methods. These in turn led to the preparation of highly reactive pentafulvenoid chloroformamidinium salts and 6-chloropentafulvenes which open an easy access to stabilized s-indacenes, 2-azapentalenes and 5-aza-azulenes besides other ring systems. The first isolable s-indacenes provide an opportunity to study the influence of substituents on the bonding character of the 1 2Φ-electron system. Different cycloaddition reactions turned out to be a versatile method for annelations and homologizations of nonbenzenoid polycyclic conjugated systems. In the persuit of this strategy azulenes could be transformed into pentalenes, heptalenes as well as cyclopentacyclononenes. © 1982 IUPAC