Abstract
TAMOF‐1, a homochiral metal‐organic framework (MOF) constructed from an amino acid derivative and Cu(II), was investigated as a heterogeneous catalyst in kinetic resolutions involving the ring opening of styrene oxide with a set of anilines. The branched products generated from the ring opening of styrene oxide with anilines and the unreacted epoxide were obtained with moderately high enantiomeric excesses. The linear product arising from the attack on the non‐benzylic position of styrene oxide underwent a second kinetic resolution by reacting with the epoxide, resulting in an amplification of its final enantiomeric excess and a concomitant formation of an array of isomeric aminodiols. Computational studies confirmed the experimental results, providing a deep understanding of the whole process involving the two successive kinetic resolutions. Furthermore, TAMOF‐1 activity was conserved after several catalytic cycles. The ring opening of a meso‐epoxide with aniline catalyzed by TAMOF‐1 was also studied and moderate enantioselectivities were obtained.
Highlights
Metal-organic frameworks (MOFs) are porous coordination polymers composed of organic linkers and metal centers or clusters
In order to expand the scope of this reaction, 10 mol% of TAMOF-1 was used as the catalyst in the reaction of rac-1 and o-anisidine 3, with similar results to those reported for aniline being observed (51% conv.; 60% ee for (R)-4b and 35% ee for (S)-4l; see Scheme 2 and Table ESI2 for details)
TAMOF-1 is a recyclable catalyst for the efficient kinetic resolution of rac-styrene oxide (1) with a set of anilines, yielding secondary amino alcohols
Summary
Metal-organic frameworks (MOFs) are porous coordination polymers composed of organic linkers and metal centers or clusters. With high porosities and thermal stabilities, these materials have captured the attention of many researchers due to their remarkable chemical and physical versatility. They have been used as gas storage and (chiral) separation materials, sensors, LEDs, drug delivery materials and catalysts, among other applications. Homochiral MOFs have already been used as enantioselective catalysts for directing the preferential formation of a stereoisomer from a pro-chiral substrate (for instance, in the cyanosilylation of aldehydes, epoxidation of alkenes, additions to carbonyl groups, carbonyl-ene and Diels-Alder reactions, cyclopropanations, aldol reactions, and the ring opening of meso-epoxides with nucleophiles ). The interesting properties of TAMOF-1 21 (i.e., capability of chiral recognition inside wide channels combined with broad tolerance to solvents) prompted us to study its catalytic activity in kinetic resolutions within confined spaces. Computational studies provided a deep understanding of the whole process, based on the different reactivity of the substrates when confined in the helical channels of TAMOF-1
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