Stereoselective Organocatalytic Synthesis of α,α-Difluoro-γ,γ-Disubstituted Butenals.

A highly stereoselective reaction of α,α-difluoro-γ,γ-disubstituted butenals 2 bearing two different substituents at the γ position has been developed with an organocatalytic system of l-proline (30 mol %) and salicylic acid (60 mol %). This novel reaction demonstrated a wide substrate scope and excellent E stereoselectivity in most cases. The obtained difluorinated aldehyde 2a was applied as a useful synthetic precursor for constructing 3,3-disubstituted allylic difluoride moieties.