Cycloaddition/aromatization 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. Selective deprotections lead to phthalimide/phthalate derivatives with an ortho-phosphonic acid function. © Georg Thieme Verlag Stuttgart · New York.