Manufacturing molecules with predefined structural and electronic properties is one of the central tasks in surface science nowadays. We investigate the thermal induced cyclization of dibromo-diphenyl-pyrene on Au(111) using scanning tunneling microscopy (STM) and spectroscopy. We show that precursor molecules self-assemble on Au(111) and form by annealing intermediate structures assembled in characteristic dimers or tetramers. By further annealing the surface, we can cleave methyl bromide groups and synthetize diindeno-pyrene molecules, as shown by high resolution STM images and dI/dV maps of the electronic orbitals. Density functional theory (DFT) and electron scattering quantum chemistry (ESQC) calculations confirm the experimental results.