Titanium Salalen Catalysts Based on cis-l,2-Diaminocyclohexane: Enantioselective Epoxidation of Terminal Non-Conjugated Olefins with H2O2

摘要

In 2005, Katsuki et al. introduced titanium salalen complexes, such as 1 (Scheme 1), as novel and highly enantioselective catalysts for the asymmetric epoxidation of a variety of nonfunctionalized olefins (both conjugated and non-conjugated) using hydrogen peroxide as the oxidant. Salalen ligands are mono-reduced salens, carrying one imine and one amine functionality. For example, the catalyst 1 was reported to effect the epoxidation of 1,2-dihydronaphthalene with quantitative yield and over 99% ee. Even more remarkably, the epoxidations of 1-octene and vinyl cyclohexane were reported to proceed with 85% yield/82% ee, and 72% yield/95% ee, respectively. 1-Octene in particular is a terminal olefin notoriously difficult to epoxidize asymmetrically—the epoxide yields/enantioselectivities achieved by Katsuki etal. in 2005/2007 were the highest ever reported.