Unsaturated sultones with normal, medium and large ring sizes were efficiently synthesized by ring closing metathesis (RCM) of sulfonates. The resulting α,β-unsaturated sultones act as dienophiles in intermolecular Diels-Alder reactions. A first cyclic sulfate formation through RCM has been discovered, and a rapid access to β-lactams fused to a sultam moiety of variable ring size was developed from inexpensive, commercially available starting materials using RCM as the key operation. An efficient RCM of 4-vinyl-azetidin-2-ones to give 1-aza-bicyclo[4.2.0]oct-4-en-8-ones is also described.