EtAlCl2-Catalyzed Reactions of Alkenes with Electrophillic Cyclopropanes. A New Cyclopentane Annelation Reaction

Article abstract of DOI:10.1021/jo00373a010

Treatment of 1,1-di-, tri-, and tetrasubstituted alkenes with diethyl cyclopropane-1,1-dicarboxylate (1) and 2 equiv of EtAlCl2 gives zwitterions which collapse to cyclopentanedicarboxylates in good to excellent yield.This reaction provides a general procedure for the annelation of cyclopentanes to alkenes.The intermediate zwitterions undergo the 1,2-hydride and -methyl shifts characteristic of carbocations, although these side reactions are generally minor.Diethyl 2-methylcyclopropane-1,1-dicarboxylate (38) reacts similarly with alkenes at the more substituted carbon of 38 to give 3-methylcyclopentane-1,1-dicarboxylates.Diethyl 2,2-dimethylcyclopropane-1,1-dicarboxylate (46) rearranges in the presence of EtAlCl2 to diethyl isobutylidenemalonate, which reacts with alkenes and is reduced by EtAlCl2.The intramolecular Lewis acid induced addition of alkenes to cyclopropanedicarboxylate esters occurs analogously.