Of the suite of single-atom insertion, deletion, and transmutation reactions developed to date, carbon-atom insertions afford a unique opportunity. Carbon-atom insertion methods can modify the core of a given scaffold while also offering the ability to append new functionalities to the resultant core. The Levin group has a deep interest in expanding both the cores amenable to such transformations, specifically heteroarenes, as well as developing new reagents and methods to gain precise control over the functionality inserted. The first chapter of this thesis will detail the current methods available to perform carbon insertion with respect to the heterocycles accepting the carbon atom and the reagents used to do so. The second chapter will examine the use of chlorodiazirines as a carbon insertion reagent to expand abundant heteroarenes, pyrazoles and indazoles, to their value-added pyrimidine and quinazoline products. The third chapter contains a collaborative effort with the Nagib group, showcasing the impacts of reagent innovation by using trichloromethyl species as chlorocarbene precursors for the expansion of indoles into quinolines. Lastly, the final chapter will build upon the limitations observed with many of these methods, unveiling a new radical-based approach to carbon atom insertion. This work will demonstrate the insertion of a single C-H into indoles and pyrroles, providing the first regioselective synthesis of pyridines from pyrroles.