The Standard Model of particle physics is one of the most successful theories ever built. It has been tested to unprecedented energies. However, despite its great success, there are still questions which remain open such as the hierarchy mass problem or the unification of the strong and electroweak forces. This lead to the edification of new theories called theories Beyond the Standard Model (BSM theories). This talk focuses on two specific BSM theories, the so called Grand Unification Theory (GUT models) which try to unify the strong and electroweak forces by use of an extended gauge group and the extra-dimensions (ED) scenario which aims at solving the hierarchy mass problem by introducing new spatial dimensions of finite size. They both predict the existence of new heavy gauge bosons such as a Z' or a graviton which could manifest itself through a peak in the di-electron invariant mass spectrum. I will give a very brief theoretical introduction and present the CMS experiment. The analysis strategy will be reviewed as well as the selection. Data-driven methods to derive the selection efficiencies and the background contributions will be introduced. Finally, results on exclusion limits on Z' and graviton masses will be given.