4 , in benzene under reflux to afford the novel 4,6-spirocycle in moderate yield. The deep-blue crystals of the spirocycle are airstable and high melting in nature. The spiro phosphorus atom subtends a four-membered P V S VI N 2 ring which is saturated, and a six-membered P V S IV 2 N 3 ring which is unsaturated. The single-crystal X-ray structure of this first example of the spirocycle reveals a planar PSN 2 ring and a puckered PS 2 N 3 ring and the molecule is symmetric in nature.A new synthetic route to cyclophosphadithiatriazines 883