Irradiations of α-fluoro-α,β-unsaturated esters lead to the corresponding α-fluoro-β,γ-unsaturated isomers in good yields. The reaction required the use of an achiral base (typically an amine) to promote the protonation of the photodienolic intermediate. By replacing the ethyl group with a diacetone-d-glucose moiety, the reaction can be carried out in a diastereoselective manner to furnish the deconjugated esters with similar yields and selectivities up to 95%. The adducts were submitted to osmylation conditions to deliver α-fluoro-β-hydroxy-butyrolactones in one single step.
photochemistry - protonations - asymmetric synthesis - lactones - α-fluoro esters
