Mn-Salen Catalyzed Asymmetric Oxidation of Simple Olefins and Sulfides.

Abstract

Among the several Mn-salen type catalysts studied, a rationally designed Mnsalen catalyst (14) was found to be the most effective for asymmetric epoxidation of simple olefins, especially cis-disubstituted and trisubstituted olefins conjugated with aryl, alkenyl and alkynyl groups. The mechanism of asymmetrc-inducition of this reaction has been well rationalized by the proposal that olefins approach oxo-metal from the side-on to give a metallaoxetane intermediate, wherein steric and electronic repulsions between the salen ligand and the olefinic substituent dictate the orientation of the incoming olefins and, the intermediate is transformed into epoxides via a radical intermediate. Asymmetric oxidation of sulfides was also found to be effectively catalyzed by Mn-salen catalyst (21).

Metal Salen- and Salphen-Containing Organic Polymers: Synthesis and Applications

“…101a,c An isostructural chiral helical poly-Mn(III)-salen was used in the asymmetric epoxidation of styrenes, but only delivered a low selectivity of 17% ee, 101b which is higher than that for the homogenous pendant (1-6% ee), but unfortunately lower than that of other chiral salen complexes (ee up to 98%). 135 This was improved in 2005 by Gothelf and coworkers using also chiral Mn(III) salen polymers (structure in Scheme 9; see above), but this time chirality was introduced by enantiomerically pure diamines. 111 The transformation of cis-methyl styrene was performed with a cis/trans-ratio of 12:1 and an ee of 67%.…”

Synthetic Uses of Phenols

“…The stability of the salicylaldehyde imine ligand under oxidative conditions lead to the application in asymmetric oxidation reactions 291,292 . Jacobsen and coworkers employed a manganese salen complex with t-butyl groups at the 3,3 -positions and attained especially high ee for the epoxidation of disubstituted cis-alkenes (equation 79) 293 -297 .…”

The enantioselectivity of the manganese-salen complex in the epoxidation of unfunctionalized olefins and the influence of grafting

“…Given the synthetic value of chiral epoxides many catalytic systems have been developed to produce these compounds with high selectivity, with the titaniumtartrate catalyst [4][5][6][7][8][9][10] and the chiral metal-salen complex [11][12][13][14][15][16] as the most well-known. The latter complexes, originally designed by Jacobsen and Katsuki, are highly performant in the epoxidation of unfunctionalized olefins.…”