IONIC IODOCARBOCYCLIZATION REACTIONS OF 4-ALKENYLMALONATE AND 4-ALKYNYLMALONATE DERIVATIVES

The cyclization reactions of dimethyl 4-alkenylmalonate derivatives la -d in the presence Of 12 and Ti(Ot-Bu)4 proceed in a highly regio- and stereocontrolled manner (5-exo cyclization and trans addition) to giv e (iodoalkyl)cyclopentane derivatives 2 or bicyclic lactones 3 through the displacement of the iodide of 2 by an ester group. Iodocarbocycli zation reactions of dimethyl [(cycloalkenyl)alkyl]malonates 1g-i or di methyl [(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 deriv atives 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 r eactions.