paperomatization Sequence for the Synthesis of 2,3-Disubstituted Benzenephosphonates

The (4+2) cycloaddition of diethyl 1-phosphonobuta- 1,3-diene with tetracyanoethylene, (E)-1,4-diphenylbut-2-ene-1,4- dione, N-phenylmaleimide, and dialkyl acetylenedicarboxylates is described. For the last two cases, treatment of the cycloadducts with nitrobenzene and a palladium catalyst allows the aromatization. Se- lective deprotections lead to phthalimide/phthalate derivatives with an ortho-phosphonic acid function.