82 / 2023-09-20 20:35:36

Phosphonium Dication Mediated Formation of [1,3,5]Dioxazin-5-ium & [1,3,5]Oxadiazin-5-ium Cations through [2+2+1] Annulations of Small Molecules

Organophosphorus Chemistry,Phosphonium Cations,[2+2+1] Annulation Reaction,Phosphane oxide

Phosphorus in Synthetic Chemistry > 2) Phosphorus compounds as ligands

Phosphonium cations have found frequent use as intermediates in catalytic reactions and as building blocks in synthetic chemistry.^[1] Despite their well-acknowledged robustness and applicability in catalysis, the exploration of phosphonium cations for the construction of annulated compounds remain an ongoing pursuit.^[2] Moreover, by selecting suitable substituents at the phosphorus atom, novel reaction pathways and the construction of complex molecules become feasible.^[3]



In this study, we present the synthesis of imidazoliumyl-substituted phosphonium dications 1[OTf]_2, featuring a Lewis basic site with a 2-pyridyloxy substituent. 1[OTf]₂ readily reacts with aldehydes to form intermediates 2[OTf]₂.^[4] Subsequent reactions with nitriles, aldehydes, alkynes or imines result in the formation of 4a­d[OTf] via a [2+2+1] annulation reaction, accompanied by the formation of phosphane oxide 3[OTf] as a coupling product.