Palladium-catalyzed annulation of vinylic cyclopropanes and cyclobutanes

Aryl iodides substituted in the ortho position by OH, CH2OH, NH2, NHTs and CH(CO(2)Et)(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 pi-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 substitution of the palladium by the resulting anion.