MODEL STUDIES OF THE STEREOELECTRONIC EFFECT IN RH(II) MEDIATED CARBENOID C-H INSERTION REACTIONS

Electronic effects of rhodium(II) catalyzed intramolecular C-H insertion reactions of 1-methyl-1-(diazoacetyl)cyclohexane derivatives 4a-i were studied. The C-3 H/C-5 H insertion ratio is modulated by the electron donating or withdrawing capacity of the functional groups at C-3 and C-5. The general finding was that electron donating groups alpha to the C-H bond in question promote the insertion reaction. As well, we found that the ligands on the catalyst also affected product ratios. The more stabilized the carbene, i.e. with electron donating ligands, proved to be the more discriminating vis-a-vis the regiochemical outcome. We were also able to demonstrate a deuterium kinetic isotope effect for the insertion reaction symmetrical substrate 41.