The chemo-selective coupling of oxetanes and carbon dioxide to afford functional, heterocyclic organic compounds known as six-membered cyclic carbonates remains a challenging topic. Here we describe an effective method for their synthesis relying on the use of Al-catalysis. The catalytic reactions can be carried out with excellent selectivity for the cyclic carbonate product tolerating various (functional) groups present in the 2- and 3-position(s) of the oxetane ring, and the presented methodology is the first general approach towards the formation of six-membered cyclic carbonates (6MCCs) through oxetane/CO2 coupling chemistry. Apart from a series of substituted six-membered cyclic carbonates, also the unprecedented room temperature coupling of oxetanes and CO2 is disclosed giving, depending on the structural features of the substrate, a variety of five- and six-membered heterocyclic products. A mechanistic rationale is presented for their formation and support for the intermediary presence of a carbonic acid derivative is given. The presented functional carbonates may hold great promise as building blocks in organic synthesis and the development of new, biodegradable polymers.