Highly efficient approach to 4-ethoxy-5,6-dihydro-6,6-disubstituted pyran-2-ones using a combinational Lewis acid-base system

The first efficient approach to 5,6-dihydro-6.6-disubstituted pyran-2-ones was successfully achieved from the reaction between commercially available ethyl 3-ethoxvbut-2-enoate and ketones in the presence of (BF3EtO)-Et-., InBr3 and LDA. (BF3Et2O)-Et-. and InBr3 were employed as the Lewis acid to activate the ketone and LDA was employed as the Lewis base to activate ethyl 3-ethoxybut-2-enoate. Aromatic, aliphatic, and heterocyclic ketones were converted to the corresponding Mactones containing quaternary carbon atom centers in excellent yields (up to 99%) under mild conditions.