Palladium-catalyzed Ring-Opening [5+2] Annulation of Vinylethylene Carbonates (vecs) and C5-substituted Meldrum's Acids: Rapid Synthesis of 7-Membered Lactones.

A novel approach for the synthesis of unsaturated 7-membered lactones by Pd-catalyzed [5+2] dipolar cycloaddition of vinylethylene carbonates (VECs) and C5-substituted Meldrum's acid derivatives has been developed. Various Meldrum's acid derivatives worked well in this reaction under mild reaction conditions. A variety of 7-membered lactones can be accessed in a facile manner in moderate to good yields by employing easily prepared Meldrum's acid derivatives.