Ru- and Mo-Catalyzed Asymmetric Synthesis of Pyrans and Piperidines

Significance

Reported is a detailed comparison of one Mo- and four Ru-based chiral catalysts (E, and A-D, respectively) in asymmetric ring-opening/cross-metathesis (AROM/CM) reactions of oxa- and azabicycles, resulting in chiral functionalized pyrans and piperidines. Compared to the Ru-complexes, the more active Mo-complex E is the most effective desymmetrization catalyst with less reactive substrates (e.g. 3b). With more reactive 3a, oligomeric products were obtained. In contrast, the less reactive Ru-catalysts perform efficient desymmetrizations with both 4a and 4b. Although the reaction is more sluggish with 4b, higher enantioselectivity is obtained than with the Mo-catalyst.