Intramolecular Phosphinyl-Zincation of Alkynes: A Powerful Entry to Benzophosphole Oxides.

Upon reacting ortho-alkynylated secondary arylphosphine oxides with Et2Zn, we discovered that P(O)─H activation is followed upon gentle heating by phosphinyl-zincation. This unprecedented transformation stands as a phosphorus version of the silyl and germyl-zincation of alkynes recently shown to give modular access to elaborated tri and tetra-substituted alkenes. The cyclic vinyl-zinc derivative resulting from intramolecular phosphinyl-zincation was characterized by multi-nuclear NMR spectroscopy. It subsequently undergoes Cu or Pd-catalyzed derivatizations with a broad range of electrophiles. The synthetic utility of this one-pot-two-step process has been leveraged to prepare a wide range of benzophosphole oxides (BPO) with diverse substitution patterns. Furthermore, π-extended BPOs have been synthesized by C─C coupling or cyclization of C3-alkynyl / alkenyl substituted compounds and their optical properties have been analyzed.