Oxophosphonium–Alkyne Cycloaddition Reactions: Reversible Formation of 1,2-Oxaphosphetes and Six-membered Phosphorus Heterocycles

While the metathesis
reaction between alkynes and carbonyl compounds
is an important tool in organic synthesis, the reactivity of alkynes
with isoelectronic main-group R2EO compounds is
unexplored. Herein, we show that oxophosphonium ions, which are the
isoelectronic phosphorus congeners to carbonyl compounds, undergo
[2 + 2] cycloaddition reactions with different alkynes to generate
1,2-oxaphosphete ions, which were isolated and structurally characterized.
The strained phosphorus–oxygen heterocycles open to the corresponding
heterodiene structure at elevated temperature, which was used to generate
six-membered phosphorus heterocycles via hetero Diels–Alder
reactions. Insights into the influence of the substituents at the
phosphorus center on the energy profile of the oxygen atom transfer
reaction were obtained by quantum-chemical calculations.