Phosphaindazole: A Phosphorus–Carbon Aromatic Heterocycle

Making and breaking of phosphorus–phosphorus bonds

In contrast to their mostly unstable isolobal carbon counterparts, oligophosphanide anions, such as M(cyclo-P5tBu4) (M=Li, Na) and M2(P4R4) [M=Na, K; R=Ph, tBu, 2,4,6-Me3C6H2 (Mes)], have unique features, depending on their composition and structure, and are highly suitable building blocks for the synthesis of phosphorus-rich metal compounds. However, alkali metal oligophosphanediides are highly reactive and highly reducing, and a major problem is their tendency for disproportionation in reactions with electrophiles. This, however, can also give rise to a fascinating chemistry of making and breaking of P–P bonds. On the other hand, neutral cyclooligophosphines, such as cyclo-(P5Ph5), are suitable stable ligands for the formation of phosphorus-rich metal complexes.

Regioselective BF3·Et2O-catalyzed C–H functionalization of indoles and pyrrole with reaction of α-diazophosphonates

A regioselective synthesis of β-(3-indol)-β-aminophosphonates and β-(2-pyrrol)-β-aminophosphonates was developed through an intermolecular C–H insertion of α-diazophosphonates with indole and pyrrole derivatives catalyzed by BF₃·Et₂O.