title: Chemoselective Switch in the Asymmetric Organocatalysis of 5H-Oxazol-4-ones and N-Itaconimides: Addition-Protonation or [4+2] Cycloaddition.
abstract: 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.
authors.affiliation: Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, Henan University, Jinming Campus, Kaifeng, Henan, 475004, P.R. China.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhu
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University, Canberra, ACT, 2601, Australia.
authors.forename: Richmond
authors.initials: R
authors.lastname: Lee
authors.affiliation: Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, Henan University, Jinming Campus, Kaifeng, Henan, 475004, P.R. China.
authors.forename: Jiangtao
authors.initials: J
authors.lastname: Li
authors.affiliation: Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, 637371, Singapore, Singapore.
authors.forename: Xinyi
authors.initials: X
authors.lastname: Ye
authors.affiliation: Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, Henan University, Jinming Campus, Kaifeng, Henan, 475004, P.R. China.
authors.forename: San-Ni
authors.initials: SN
authors.lastname: Hong
authors.affiliation: Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, Henan University, Jinming Campus, Kaifeng, Henan, 475004, P.R. China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Qiu
authors.affiliation: ARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, Australian National University, Canberra, ACT, 2601, Australia. michelle.coote@anu.edu.au.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Coote
authors.affiliation: Key Laboratory of Natural Medicine and Immuno-Engineering of Henan Province, Henan University, Jinming Campus, Kaifeng, Henan, 475004, P.R. China. chmjzy@henu.edu.cn.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Jiang
keywords: chemoselectivity; chirality; density functional calculations; organocatalysis; synthetic methods