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