This dissertation is centered around new synthetic applications of metalloradical-carbene-transfer strategies in the synthesis of medium-sized rings, and the utilization of these new cyclic products as molecular photoswitches and synthetic platforms. In the first part of this dissertation, cobalt-based metalloradical strategies were successfully exploited in the synthesis of medium-sized ring compounds, and three types of novel 8-membered cyclic structures were developed: dibenzocyclooctenes, monobenzocyclooctadienes, and 1H-2-benzo[c]oxocins. Mechanistic investigations indicated that all these transformations proceed via cobalt(III)-carbene radicals as intermediates, which have been supported by experimental observations, computational studies, and spin trapping experiments. The second part of the thesis exhibits our findings on the employment of these 8-membered cyclic molecules. A novel T-type molecular photoswitch based on the reversible cyclization of 1H-2-benzo[c]oxocins to dihydro-4H-cyclobuta[c]isochromenes has been developed, and their switching behavior was investigated with spectroscopic studies and photophysical investigations. Alongside the photo-responsive behavior of 1H-2-benzo[c]oxocins, these 8-membered heterocycles can easily convert to other bioactive structures, including dihydronaphthalenes and 1,3-dihydroisobenzofuran-3-oxobutanoates, which are important substructures found in several bioactive molecules/enzymes that are difficult to access otherwise.