ABSTRACT
Figure 6.1 Quinoxaline (1,4-diazanaphthalene) and related diazanaph-thalenes.In addition to the medicinal applications, the electronic and spectroscopic properties of quinoxaline-embedded chromophores are particularly attractive in materials chemistry [12-36]. They have found application in the design of functional materials, such as dyes [15,16], anion receptors [17-19], chemically controllable switches [20,21], photo-and electroluminescent molecules [22-25], and organic semiconductor [26-28]. Due to easy modification of the basic skeleton, they also serve as building blocks or rigid subunits in the synthesis of shape persistent macrocycles, such as dendrimers [29,30]. Compared to hydrocarbon analogues, heteroacenes containing imine nitrogen atoms (–N=) generally have less negative reductive potential and higher electron affinity. Accordingly, considerable interest in aza-substituted acenes (polyazaacenes) has recently emerged, because of their possible application in developing useful n-type (electron transporter) semiconductor material [31-36].The pharmacological importance of quinoxalines and their utility as key intermediates in the synthesis of organic functional
materials have directed considerable research activities toward the development of synthetic strategies for the preparation of suitably substituted quinoxalines. As a result, a large number of synthetic approaches for the construction of the skeleton of such heterocycles have been described in the chemistry literature [37-42]. Considering the significant applications in the fields of medicinal, industrial, and material chemistry, the development of an efficient and versatile method for the synthesis of highly functionalized quinoxalines is still an important and requisite challenge.Among the assorted synthetic strategies for the construction of quinoxaline ring system, the classical method relying on the condensation of a 1,2-dicarbonyl compound (a-diketone) with an aromatic 1,2-diamine in presence of a suitable catalyst is nevertheless the most straightforward and commonly utilized one, Eq. (6.1) [41,42].
