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 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.
Intramolecular Carbostannation Reaction of Active Methine Compounds with an Unactivated C−C π-Bond Mediated by SnCl<sub>4</sub>−Et<sub>3</sub>N
In the presence of SnCl4 and Et3N, intramolecular carbostannation reaction of various active methine compounds having an unactivated alkenyl, alkynyl, or allenyl group proceeds in good yields with complete regioselectivity. The subsequent reaction of the resulting Sn intermediates with-some electrophiles provides functionalized cyclopentane and cyclohexane derivatives.