Carbohydrate-derived iminium salt organocatalysts for the asymmetric epoxidation of alkenes (original) (raw)
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ntroduction of a pseudoaxial substituent at a stereogenic center adjacent to the nitrogen atom in binaphthyl- and biphenyl-derived azepinium salt organocatalysts affords improved enantioselectivities and yields in the epoxidation of unfunctionalized alkenes. In the biphenylderived catalysts, the atropoisomerism at the biphenyl axis is controlled by the interaction of this substituent with the chiral substituent at nitrogen.
Reverse asymmetric catalytic epoxidation of unfunctionalized alkenes
Tetrahedron, 1999
New salen Mn(III) complexes (S,S)-6a-e prepared from tartaric-derived alicyclic C2 symmetric vicinal diamines were studied in the catalysis of the asymmetric epoxidation of unfunetionalized alkenes. Although the enantioselectivities obtained were not as high as for Jacobsen and Katsuki catalysts, the most striking result was the reversed asymmetric induction.
Iminium Salt-Catalysed Asymmetric Epoxidation using Hydrogen Peroxide as Stoichiometric Oxidant
Advanced Synthesis & Catalysis, 2008
Iminium salt organocatalysts can provide high selectivity and high efficiency in catalytic asymmetric epoxidation. They are normally used in conjunction with Oxone as the stoichiometric oxidant. Oxone, however, has limited stability and is insoluble in most organic solvents; we report here for the first time the development of a reaction system driven by hydrogen peroxide as the stoichiometric oxidant, involving an unusual double catalytic cycle.
Advanced Synthesis & Catalysis, 2020
The diastereodivergent synthesis of bridged 1,2,3,4-tetrahydroisoquinoline derivatives has been achieved by using appropriate modularly designed organocatalysts (MDOs) that are self-assembled in situ from amino acids and cinchona alkaloid derivatives. The domino Mannich/aza-Michael/aldol reaction between (E)-2-[2-(3-aryl-3oxoprop-1-en-1-yl)phenyl]acetaldehydes and ethyl or benzyl (E)-2-[(4-methoxyphenyl)imino]acetates catalyzed by MDOs gives two different diastereomers of the desired bridged tetrahydroisoquinolines in good yields and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to >99% ee). The diastereodivergence was achieved in the aldol reaction step.