Computational Study on the Mechanism and Selectivity of C-H Bond Activation and Dehydrogenative Functionalization in the Synthesis of Rhazinilam

The key platinum mediated C-H bond activation and functionalization steps in the synthesis of (-)-rhazinilam (Johnson, J.A.; Li, N.; Sames, D.J. Am. Chem. Soc. 2002, 124, 6900) were investigated using the M06 and B3LYP density functional approximation methods. This computational study reveals that ethyl group dehydrogenation begins with activation of a primary C-H bond in preference to a secondary C-H bond in an insertion/methane elimination pathway. The C-H activation step is found to be reversible while the methane elimination (reductive elimination) transition state controls rate and diastereoselectivity. The chiral oxazolinyl ligand induces ethyl group selectivity through stabilizing weak interactions between its phenyl group (or cyclohexyl group) and the carboxylate group. After C-H activation and methane elimination steps, Pt-C bond functionalization occurs through beta-hydride elimination to give the alkene platinum hydride complex.