Abstract The intermediacy of metallocarbenes in decomposition reactions of iodonium ylides with [Rh 2 (OAc) 4] was established by comparison with reactions of the corresponding diazo compounds. The sensitivity of the Rh II-catalyzed intermolecular cyclopropane formation from substituted styrenes and bis (methoxycarbonyl)(phenyliodono) methanide (1a) or dimethyl diazomalonate (1b) is identical. The Hammett plot (with σ+) has a slope of ...
