Chemoselective Switch in the Asymmetric Organocatalysis of 5 H -Oxazol-4-ones and N -Itaconimides: Addition-Protonation or [4+2] Cycloaddition
Coote, Michelle L.
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Abstract© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. We report a synthetic strategy for a chemoselective switch and a diastereo-divergent approach for the asymmetric reaction of 5H-oxazol-4-ones and N-itaconimides catalyzed by L-tert-leucine-derived tertiary amine-urea compounds. The reaction was modulated to harness either tandem conjugate addition-protonation or [4+2] cycloaddition as major product with excellent enantio- and diastereoselectivities. Subjecting the enantio-enriched cycloaddition products to a basic silica gel reagent yields the diastereomer vis-à-vis the product directly obtained under conditions for addition-protonation, thus opening a diastereo-divergent route for creating 1,3-tertiary-hetero-quaternary stereocenters. Quantum chemical studies further provide stereochemical analysis for the [4+2] process and a plausible mechanism for this chemoselective switch is proposed.
CitationZhu B, Lee R, Li J, Ye X, Hong S-N, et al. (2015) Chemoselective Switch in the Asymmetric Organocatalysis of 5 H -Oxazol-4-ones and N -Itaconimides: Addition-Protonation or [4+2] Cycloaddition . Angew Chem Int Ed 55: 1299–1303. Available: http://dx.doi.org/10.1002/anie.201507796.
SponsorsZ.J. is grateful for the grants from NSFC (grant number21072044), NCET-11-0938 and the Program for InnovativeResearch Team from the University of Henan Province(14IRTSTHN006). M.L.C. gratefully acknowledges generousallocations of supercomputing time on the National Facility ofthe National Computational Infrastructure, and financialsupport from the Australian Research Council. R.L. alsoacknowledges Dr. Xiaohe Miao (KAUST) for supplementarycomputing time.
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