Nucleophilic\nRing Opening of Donor–Acceptor\nCyclopropanes through Umpolung Reactivity of Organochlorophosphines:\nPhosphine Oxide-Functionalized Boron-Pendanted Compounds

We present a novel set of frustrated Lewis pair (FLP)\nsystems that\nexhibit a remarkable ability to promote the ring opening of donor–acceptor\ncyclopropanes (DACs). This FLP-promoted protocol offers umpolung reactivity\nof R<sup>1</sup>R<sup>2</sup>PCl/CN (R<sup>1</sup>, R<sup>2</sup> =\naryl, alkyl) toward DACs via nucleophilic ring-opening reactions to\nprovide phosphinated boron-pendanted diester compounds. This novel\napproach exhibits the dual role of BF<sub>3</sub>·OEt<sub>2</sub> as an activator and a reactant. The resulting compounds were found\nin both the keto and enol forms, with the majority being in the keto\nform, according to NMR analysis. The enol form was identified by single-crystal\nXRD analysis, and DFT calculations indicated that the keto form is\nmore stable than the corresponding enol form.