CARBENOID REACTIONS IN RHODIUM(II)-CATALYZED DECOMPOSITION OF IODONIUM YLIDES

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 sigma(+)) has a slope of -0.47. Iodonium ylides and diazo compounds afford the same products in [Rh-2(OAc)(4)]-catalyzed cyclopropane formations, cycloadditions, and intramolecular CH insertions, and exhibit the identical selectivity in intramolecular competitions for cyclopropane formation and insertion. The intramolecular CH insertion of the ylide 20c, when carried out in the presence of a chiral catalyst ([Rh-2{(-)-(S)-ptpa}(4)]), results in formation of 21a having an ee of 67%, identical to the ee obtained with the diazo compound 20b.