Fluoroallylboration-Olefination for the Synthesis of (Z)-4,4-Difluoropent-2-enoates and 5,5-Difluoro-5,6-dihydropyran-2-ones

Horner-Wadsworth Emmons (HWE) or Still-Gennari olefination of TBS-protected 3,3-difluoro-4-hydroxy-2-ones, derived from the difluoroallylboration of aldehydes, provides the Z-isomer of 4,4,-difluoropent-2-enoates. These, upon hydrolysis, followed by Yamaguchi cyclization, afford 5,5-difluoro-4-methyl-5,6-dihydro-alpha-pyrones in high yields.