Nucleophilic Ring Opening of Donor-Acceptor Cyclopropanes through Umpolung Reactivity of Organochlorophosphines: Phosphine Oxide-Functionalized Boron-Pendanted Compounds.

ABSTRACT

We present a novel set of frustrated Lewis pair (FLP) systems that exhibit a remarkable ability to promote the ring opening of donor-acceptor cyclopropanes (DACs). This FLP-promoted protocol offers umpolung reactivity of R1R2PCl/CN (R1, R2 = aryl, alkyl) toward DACs via nucleophilic ring-opening reactions to provide phosphinated boron-pendanted diester compounds. This novel approach exhibits the dual role of BF3·OEt2 as an activator and a reactant. The resulting compounds were found in both the keto and enol forms, with the majority being in the keto form, according to NMR analysis. The enol form was identified by single-crystal XRD analysis, and DFT calculations indicated that the keto form is more stable than the corresponding enol form.