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

Ortho-alkynylated secondary arylphosphine oxides undergo phosphinyl-zincation upon reaction with Et₂Zn under gentle heating. The ensuing C3-zincated benzophosphole oxides have been characterized by multi-nuclear NMR spectroscopy. They are readily derivatized via Cu or Pd-catalyzed C─C cross-couplings. This one-pot-two-step process gives straightforward and efficient access to a wide range of benzophosphole oxides with diverse substitution patterns.

Abstract

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.

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