Conclusive Evidence for a Retention−Retention Pathway for the Molybdenum-Catalyzed Asymmetric Alkylation

Enantiomerically enriched, deuterated branched carbonates (Z)-(S)-PhCH(O2COMe)−CHCHD (1a), (Z)-(R)-PhCH(O2COMe)CHCHD (2a), and linear carbonate (E)-(S)-PhCHCHCHD(O2COMe) (12) were employed as probes in the Mo-catalyzed asymmetric allylic alkylation with sodium dimethyl malonate, catalyzed by ligand complex 10 derived from the mixed benzamide/picolinamide of (S,S)-trans-diaminocyclohexane and (norbornadiene)Mo(CO)4. X-ray crystallography, along with solution NMR structural analysis of the π-allyl intermediate and competition experiments, conclusively established the reaction proceeded via a retention−retention pathway. This mechanism contrasts with that defined for Pd-catalyzed allylic alkylations, which proceed via an inversion−inversion pathway.