Modular and diversity-oriented synthetic approaches to benzoheteroles and dibenzoheteroles

Abstract

Benzo[b]heterole represents an important class of heterocycles that is comprised of a variety of functional molecules. For example, indole and benzofuran are ubiquitously present in biologically active natural and unnatural compounds. As such, a number of methods have been developed for their synthesis. On the other hand, benzoheteroles containing other Group 13–16 elements are now gaining interested, especially for their unique optical and electronic properties that warrant their applications in various areas including electronics, imaging, and sensing. Nevertheless, synthetic methods for these heterocycles have been relatively limited. This thesis describes the development of new synthetic approaches that enable expedient, modular, and divergent synthesis of benzoheteroles and related heterocycles from readily available starting materials. Our main approach capitalizes on the cobalt-catalyzed "migratory arylzincation" reaction of an alkyne, which affords an ortho-alkenylarylzinc species as a key intermediate. It has been demonstrated that this common intermediate can be readily transformed into several members of the benzoheterole family such as benzothiophene, benzoselenophene, benzotellurophene, and benzophosphole, in a one-pot manner for some cases. Besides benzoheteroles, we have also established a new synthetic route to dibenzoheteroles based on the facile two-step conversion of 2-iodobiaryls into 2,2'-diiodobiaryls via a sequence of oxidative cyclization–iodinative ring opening. Collectively, the new approaches developed in this study have opened access to a diverse set of hitherto inaccessible or difficult-to-access functionalized benzoheteroles and related heterocycles, which may hold promise for applications as functional materials.