A Convenient Synthesis of 1,2,4- and 1,3,4-Azadiphospholes

A new synthetic route to functionalized neutral and anionic azadiphospholes from easily accessible starting materials is described. Equimolar reaction of Na(OCP) and N-(2,6-dimethylphenyl)pivalimidoyl chloride 2 a cleanly affords the imidoxy-functionalized 1,2,4-azadiphosphole 3 a. Using Na(OCP) and imidoyl chloride in a 2:1 ratio leads to an anionic four-membered ring Na[4 a], which has been structurally characterized. During 16 h at room temperature, Na[4 a] rearranges to the anionic 1,3,4-azadiphospholide Na[5 a] with release of carbon monoxide. Applying the more sterically demanding N-(2,6-diisopropylphenyl)pivalimidoyl chloride allows isolation of the 1,3,4-azadiphospholide Na[5 b] in good yield (>70 %). Possible mechanisms leading to the new isomeric azadiphospholides have been investigated with the aid of high-level composite calculations.