Diastereoselective Palladium-Catalyzed Formate Reduction of Allylic Carbonates as a New Entry into Propionate Units

The diastereoselective palladium-catalyzed formate reduction of allylic carbonates is described. Reduction of allylic carbonates under mild conditions (Pd(OAc)₂ (2.5−5 mol %), [n-Bu₃PH]BF₄ (2.5−5 mol %), HCO₂H/Et₃N (1:2) (3 equiv), CH₃CN (0.05M), 40 °C) affords the terminal olefin as the syn isomer in good yields and modest to excellent diastereoselectivity. These compounds, which are useful building blocks for the synthesis of polypropionate units, are the synthetic equivalent of the products obtained from an aldol reaction of an α-methyl-β,γ-unsaturated aldehyde.