Efficient synthesis of 3-chloromethyl-2(5H)-furanones and 3-chloromethyl- 5,6-dihydropyran-2-ones via the PdCl₂-catalyzed chlorocyclocarbonylation of 2,3- or 3,4-allenols

(Chemical Equation Presented) A mild and efficient methodology involving PdCl₂-catalyzed chlorocyclocarbonylation of 2,3- or 3,4-allenols with CuCl₂ for the synthesis of 3-chloromethyl-2(5H)-furanones and 3-chloromethyl-5,6-dihydropyran-2-ones was developed. This reaction proceeded in a highly regioselective manner, i.e., the chlorine atom was introduced to the terminal position of the allene moiety while the lactone linkage was formed between the center carbon atom of the allene moiety and the hydroxyl oxygen, which was established by the X-ray single crystal diffraction study of γ-lactone 3p. The highly optically active 3-chloromethyl-2(5H)-furanones could be easily prepared from the readily available optically active 2,3-allenols. A mechanism for this reaction was proposed.