( E )‐Dimethyl 2‐Oxopent‐3‐enylphosphonate: An Excellent Substrate for Cross‐Metathesis – Easy Access to Functionalized Heterocycles

Simple and efficient access to tetrahydrofurans, tetrahydropyrans, and pyrrolidines through a tandem cross‐metathesis/1,4‐addition process from ( E )‐dimethyl 2‐oxopent‐3‐enylphosphonate and N ‐protected ω‐unsaturated amines or alcohols under microwave irradiation is described. As the Grubbs–Hoveyda catalyst is highly chemoselective, a diversity of functionalized heterocycles were synthesized. Furthermore, an additional functionalization can be performed due to the presence of a side chain that possesses a ketophosphonate at the C2 position of the heterocycle.