Synthesis of 1,1-bisphosphono-2-aza-1,3-dienes, a new class of electron-deficient azadienes

1,1-Bisphosphono-2-aza-1,3-dienes are formed by 1,4-dehydrohalogenation of the corresponding N-(bisphosphonomethyl)-α-haloimines in moderate to good yields. The precursors could be formed by condensation of bisphosphono-amines and the corresponding α-haloaldehydes.