Samariumu Diiodide Promoted [alpha]-Methylene-[gamma]-lactone Synthesis

Samarium diiodide promoted reductive coupling between ethyl 2-(bromomethyl)acrylate (1) and carbonyl compounds (2) was studied. The 2-ethoxycarbonyl allylation with benzaldehyde, hexanal, acetophenane, and benzophenone proceeded in tetrahydrofuran-hexamethylphosphoric triamide at -78 °C to room temperature, and the corresponding a-methylene-rbutyrolactones (3) were produced in moderate yields. However, the reaction with cyclohexanone and diethyl ketone only resulted in a reductive dimerization of 1; no desired 3 were obtained and diethyl 2, 5-bis(methylene)hexanedioate was produced in 50-70% yields. When the reaction was carried out by using ethyl 2-(acetoxymethyl)acrylate 7 instead of 1 as a precursor in the presence of catalytic amount of tetrakis(triphenylphosphine)palladium complex, the corresponding 3 were obtained from the reaction not only with benzaldehyde, hexanal, and acetophenone but also cyclohexanone which did not give 3 in the reaction with 1.