Enantioselective ring opening of epoxides with TMSN3 by macrocyclic oligomer-supported Cr(III)–salen catalysts

Combinatorial Chemistry Online Volume 17, Issue 7, July 2015

“…The influence of the linker length and the oligomeric support on the activity and the enantioselectivity of the catalysts has been investigated in the asymmetric ring opening of a mesoepoxide and the kinetic resolution of terminal epoxides. For both reactions, all three catalysts exhibited significantly higher catalytic efficiency than the unsupported monomeric Cr(III)-salen catalyst [11].…”

Asymmetric Ring-Opening of Epoxides Catalyzed by Metal–Salen Complexes

“…The catalysts could be recovered by precipitation with acetone and recycled up to five times with maintained reactivity and enantioselectivity. Inspired by Weck's [48] work on hydrolytic kinetic resolution (HKR) of terminal epoxides, Liu and coworkers [49] studied the catalytic properties of macrocyclic oligomer-supported Cr-salen catalysts in the ARO of cyclohexene oxide with TMSN 3 . Catalysts with different linker lengths between the salen complex and the oligomers were synthesized and compared (catalysts 29-31, Figure 10).…”

“…Liu and coworkers investigated the macrocyclic oligomer-supported Cr-salen catalysts 29-31 (Figure 10) in the KR of 1,2-epoxyhexane and propylene oxide [49]. The same trend as in the ARO of meso-epoxides was found, where a shorter linker between the Cr-salen complex and the macrocycle increased the reaction rate and gave the highest yield (45-48%), while a longer linker gave better enantioselectivity (83-84% ee) for the ring-opened product.…”

Chiral Salen Complexes for Asymmetric Heterogeneous Catalysis: Recent Examples for Recycling and Cooperativity

“…A similar strategy was followed by Liu et al for the preparation of oligomer cyclooctene-supported Cr-salen catalysts and they studied their efficiency in the enantioselective ring-opening of meso-epoxides and in the kinetic resolution of terminal epoxides with TMSN 3 . [34] Introduction of different linkers demonstrated that their length influenced greatly the catalysts activity. Indeed, the shortest linker led to the highest reaction rate, due to a close interaction of the Cr-salen moieties, whereas Scheme 6.…”

“…Bifunctional Lewis acid/ammonium salts demonstrated further efficient cooperativity to perform epoxide ring opening by bromide ion. [78] The chiral Lewis acid activated the epoxide and the enantioselective nucleophilic attack occurred by the bromide ion directed by the ammonium moiety, anchored onto the salen ligand (34,Scheme 22). β-Functionalized alcohols possessing two adjacent stereocenters were obtained with high enantioselectivities, as highly valuable substrates.…”