Regioselective and reductive cleavage of allyl ethers by NaBH4-HOAc

β-Enaminals were successfully synthesized in good to excellent yields by the reaction of C2-formylglycals with primary amines. Subsequent reaction with NaBH4 in HOAc led to unexpected reductive cleavage of allyl ether, i.e., the hydrodealkoxylation took place to produce the corresponding 3-deoxy-β-enaminals. In contrast, the reaction of β-enaminals with Zn/HOAc performed H4-elimination to afford a diene product. The result was attributed to the formation of a common eneiminium ion intermediate, and the different reduction reactivity.