Pentacoordinate Organosilicate-Catalyzed Michael Addition of β-Keto Esters to 3-Buten-2-one

The Michael addition of β-keto esters to 3-buten-2-one (methyl vinyl ketone, MVK) in the presence of a pentacoordinate organosilicate was investigated. Ethyl 2-oxo-1-cyclohexanecarboxylate reacted with MVK in the presence of potassium bis(1,2-benzenediolato)phenylsilicate to furnish ethyl 2-oxo-1-(3-oxo-1-butyl)-1-cyclohexanecarboxylate in 96% isolated yield. Ethyl 2-oxo-1-cyclopentanecarboxylate, ethyl 2-oxo-1-cyclooctanecarboxylate, ethyl 2-methyl-3-oxobutanoate, and ethyl 2-ethyl-3-oxobutanoate also reacted with MVK in the presence of potassium bis(1,2-benzenediolato)phenylsilicate to produce the corresponding 1,4-adduct in moderate to good yields. In these reactions, the silicate might work as both a Lewis acid catalyst and a Brønsted base catalyst at the same time.