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Chemoselective Switch in the Asymmetric Organocatalysis of 5 H ‐Oxazol‐4‐ones and N ‐Itaconimides: Addition–Protonation or [4+2] Cycloaddition
Author(s) -
Zhu Bo,
Lee Richmond,
Li Jiangtao,
Ye Xinyi,
Hong SanNi,
Qiu Shuai,
Coote Michelle L.,
Jiang Zhiyong
Publication year - 2016
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201507796
Subject(s) - cycloaddition , protonation , stereocenter , chemistry , enantioselective synthesis , organocatalysis , reagent , tertiary amine , amine gas treating , diastereomer , combinatorial chemistry , stereochemistry , catalysis , organic chemistry , ion
Abstract We report a synthetic strategy for a chemoselective switch and a diastereo‐divergent approach for the asymmetric reaction of 5 H ‐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.