Chemoselective Switch in the Asymmetric Organocatalysis of 5H-Oxazol-4-ones and N-Itaconimides: Addition-Protonation or [4+2] Cycloaddition.

Citation data:

Angewandte Chemie (International ed. in English), ISSN: 1521-3773, Vol: 55, Issue: 4, Page: 1299-303

Publication Year:
2016
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Repository URL:
http://hdl.handle.net/10754/597772
PMID:
26662073
DOI:
10.1002/anie.201507796
Author(s):
Zhu, Bo; Lee, Richmond; Li, Jiangtao; Ye, Xinyi; Hong, San-Ni; Qiu, Shuai; Coote, Michelle L.; Jiang, Zhiyong
Publisher(s):
Wiley-Blackwell
Tags:
Chemical Engineering; Chemistry; Chemoselectivity; Chirality; Density functional calculations; Organocatalysis; Synthetic methods
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article description
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.