Gas-Phase Tandem Cyclisation as a route to fused- Ring Heterocycles

The seies of four new stabilised phosphorus ylides 16-19 have been prepared and fully characterised. Upon FVP at 850deg they undergo extrusion of Ph3PO. Loss of Me· and tandem cyclisation leading to the four new heterocyclic compounds benzofuro [5,4-b] benzofuran 20, benzothieno [5,4-b] benzofuran 21, benzothieno [3,2-e] benzofuran 22 and benzothieno [5,4-b] benzothiophene 23. Both 21 and 22 are the firest representative of previously unknown ring system. (Author's) 9 refs