Advances in the synthesis of indolizines and their π-expanded analogues: update 2016-2024

Abstract

Indolizine (pyrrolo[1,2-a]pyridine) is of the isomers of indole. Diversity of synthetic approaches leading to indolizine skeleton is unrivalled, when compared to many other heterocycles of this size. Whereas new methods continue to be developed, researchers are coming back to classical Chichibabin-type strategies. Increasing availability of densely functionalized pyrrole derivatives make it possible to expand the scope of indolizine synthesis from these substrates. In this article, we will describe the progress in the development of new strategies leading to indolizine and its π-expanded analogs during the period 2016-2024. First of all, we will discuss the synthetic pathways leading to the indolizine core starting from pyridine followed by describing methods starting from pyrrole derivatives. Finally, we will focus on π-expanded indolizines describing also their optoelectronic properties. Although certain synthetic limitations exist, the newly developed methodologies provided impetus for numerous explorations that use indolizines. We anticipate that our review will help motivate further advances in indolizines’ synthesis.