E-Selective Horner–Wadsworth–Emmons reaction of 2-OBO-cyclopentanone for the synthesis of rac-N-Cbz-Gly-Ψ[(E)-CFC]-Pro-OH dipeptide isostere

The Horner–Wadsworth–Emmons reactions of ethyl 2-fluoro-2-diethylphosphonoacetate with 2-(4-methyl-2,6,7-trioxabicyclo[2.2.2]octan-1-yl)cyclopentanone (2-OBO-cyclopentanone) using n-butyllithium furnished the corresponding tetra-substituted fluoroolefin in an E-selective manner (E:Z = 95:5). A facile synthesis of rac-N-Cbz-Gly-Ψ[(E)-CFC]-Pro-OH as a dipeptide isostere was achieved based on the E-selective Horner–Wadsworth–Emmons reaction.