Palladium-catalyzed annulation of vinylic cyclopropanes and cyclobutanes

Article abstract of DOI:10.1016/0040-4020(96)00011-7

Aryl iodides substituted in the ortho position by OH, CH₂OH, NH₂, NHTs and CH(CO₂Et)₂ groups react with vinylic cyclopropanes and cyclobutanes in the presence of a palladium catalyst and an appropriate base to afford good yields of heterocycles and carbocycles. The annulation products apparently arise by (1) palladium(0) formation and insertion into the carbon-iodine bond of the aryl iodide to generate an arylpalladium intermediate, (2) arylpalladium addition across the carbon-carbon double bond of the alkene, (3) ring-opening of the cyclopropane or cyclobutane by carbon-palladium beta elimination, (4) rearrangement of the resulting unsaturated alkylpalladium compound to a π-allylpalladium compound by a series of reversible palladium hydride beta elimination and readdition steps, (5) anion formation by removal of a proton from the functional group present on the arene, and (6) nucleophilic substitutions of the palladium by the resulting anion.