Abstract
Cycloisomerization reactions involving C–P bond formation have been overlooked for the synthesis of P-heterocycles. In this work, we developed a simple, efficient and versatile route to synthesize benzophosphole oxides by reacting ortho-alkynyl secondary phosphine oxides with 5 mol% AgSbF6. Mechanistic investigations revealed a radical-chain mechanism involving phosphinoyl radicals as key intermediates and rare 5-endo-dig cyclization as a key step, rather than the π-activation of the C![[triple bond, length as m-dash]](https://www.rsc.org/images/entities/char_e002.gif)
C triple bond. The transformation is both efficient and versatile. It effectively complements alternative intermolecular approaches. It works with a wide diversity of substitution patterns (alkynyl, benzo and phosphorus moieties) and enables the exquisite control of regioselectivity. Post-functionalization via direct C–H vinylation of the C2 position is also substantiated.
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