Ionic Iodocarbocyclization Reactions of 4-Alkenyl- and 4-Alkynylmalonate Derivatives

Article abstract of DOI:10.1021/jo00063a033

The cyclization reactions of dimethyl 4-alkenylmalonate derivatives 1a-d in the presence of I2 and Ti(Ot-Bu)4 proceed in a highly regio- and stereocontrolled manner (5-exo cyclization and trans addition) to give (iodoalkyl)cyclopentane derivatives 2 or bicyclic lactones 3 through the displacement of the iodide of 2 by an ester group.Iodocarbocyclization reactions of dimethyl <(cycloalkenyl)alkyl>malonates 1g-i or dimethyl <(methylenecycloalkyl)alkyl>malonates 1j and 1k proceed regio- and stereoselectively to give fused ring compounds or spiro compounds, respectively, as single isomers.Similar reactions of 4-alkynyl derivatives 5 give preferentially E-iodomethylene cyclopentane derivatives 6.An ionic mechanism rather than a radical mechanism is suggested on the basis of the regioselectivity and stereospecificity of the above reactions.