The reaction of biphenylene (1) with an excess of lithium powder (1:14 molar ratio) and a catalytic amount of DTBB (10mol%) in THF at room temperature leads to the formation of the dilithiated species I by reductive opening of the four-membered ring. Further reaction of this intermediate with different electrophiles [Electrophile=H 2 O, D 2 O, Me 3 SiCl, t-BuCHO, Et 2 CO, n-Pr 2 CO, (CH 2 ) 5 CO, Ph 2 CO and adamantanone] at 0°C yields the corresponding products 2, after hydrolysis with water. Cyclisation of some representative examples of compounds 2 with H 3 PO 4 gives the corresponding dibenzoxepines 3.