Synthesis of dibenzo[c,e][1,2]diazocines-a new group of eight-membered cyclic azo compounds

Despite of a remarkable ring strain hitherto unknown dibenzo[c,e][1,2]diazocines 3 could be prepared from readily available azo compounds 4 under mild Ullmann-type reaction conditions. The obtained stereoisomers of the new heterocycles 3 were structurally assigned by 2D NMR experiments and DFT calculations.