Synthesis of <i>P</i>-Substituted 5- and 6-Membered Benzo-Phostams: 2,3-Dihydro-1<i>H</i>-1,2-benzazaphosphole 2-Oxides and 2,3-Tetrahydro-1<i>H</i>-1,2-benzazaphosphinine 2-Oxides
Several approaches were developed for the preparation of phosphorus-substituted 5- and 6-membered benzophostams. Carbodiimide-promoted cyclization of zwitterionic aminophosphinates derived from a nitrobenzene precursor accomplished the cyclization in good yields. Alternatively, a novel copper-catalyzed cross-coupling between a phosphonamide and a bromobenzene precursor produced the heterocycles in
5- And 6-membered ring phostams are functionalized at nitrogen and carbon through the use of metal-catalyzed reactions, such as copper-catalyzed cross-coupling and palladium-catalyzed reductive Heck reaction. Different approaches are compared for the heterocyclization step and the introduction of the substituents.