Stereoselective synthesis of 3-spiro-α-methylene-γ-butyrolactone oxindoles from Morita–Baylis–Hillman adducts of isatin

A concise stereoselective synthesis of 3-spiro-α-methylene-γ-butyrolactone oxindoles from Morita–Baylis–Hillman adducts of isatin in excellent yield has been achieved following a three-step reaction sequences viz. (1) Isomerisation of the Morita–Baylis–Hillman adducts of isatin with trimethyl orthoformate and montmorillonite K10 clay catalyst, (2) a second Morita–Baylis–Hillman reaction with formaldehyde, and (3) an acid catalysed lactonization. The structure and stereochemistry of the products were assigned by X-ray crystallographic and NMR spectroscopic studies. Formation and mechanism of the minor product spirofuran oxindoles and a one-pot base promoted second Morita–Baylis–Hillman adduct formation–lactonization reaction have also been achieved.