Asymmetric transfer of carbenes with phenyliodonium ylides.

Phenyliodonium ylides, readily available upon treatment of CH-acidic compounds such 1,3-dicarbonyl derivatives with iodobenzene diacetate, react in the presence of rhodium(II) or copper catalysts to afford products derived from carbenoid pathways. Chemo- and enantioselectivity of the reactions are identical to those of the corresponding diazocompounds, indicating metallocarbene intermediates with both precursors. An exception to this occurs in the intramolecular cyclopropanation of phenyliodonium ylides, where a competing uncatalyzed pathway intervenes at room temperature. When phenyliodonium ylides are generated in the presence of Rh(II) catalysts and olefins, they react in situ to afford cyclopropanes.