title: A Highly Efficient Chirality Switchable Synthesis of Dihydropyran-Fused Benzofurans by Fine-Tuning the Phenolic Proton of β-Isocupreidine (β-ICD) Catalyst with Methyl.
abstract: A highly enantioselective β-isocupreidine (β-ICD) catalyzed synthesis of dihydropyran-fused benzofurans through [4+2] cycloaddition of allenoates and benzofuranone alkenes was developed. Switchable chirality inversion of cycloaddition products was achieved by replacing the phenolic proton of the catalyst with a methyl, demonstrating an amazing effect of minimal structural variation on inverting enantioselectivity. DFT calculations were utilized to elucidate the origin of the observed phenomena. Computation also provided a clue for a rational design in which the multi-hydrogen bond with the alcohol additive was found to improve the enantioselectivity of the cycloaddition. Finally, the substrate scope was examined, in which a number of functionalized dihydropyran-fused benzofurans could be obtained in high yields (up to 97 %) with very good regio- (>20:1) and enantioselectivities (up to 98:2 e.r.).
authors.affiliation: State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University, Tianjin 300071 (P.R. China).
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University, Tianjin 300071 (P.R. China).
authors.forename: Chen
authors.initials: C
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University, Tianjin 300071 (P.R. China).
authors.forename: Xiao-Song
authors.initials: XS
authors.lastname: Xue
authors.affiliation: State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University, Tianjin 300071 (P.R. China). xin_li@nankai.edu.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.affiliation: State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University, Tianjin 300071 (P.R. China). chengjp@nankai.edu.cn.
authors.forename: Jin-Pei
authors.initials: JP
authors.lastname: Cheng
keywords: Lewis base; chirality inversion; cycloadditions; density functional calculations; switchable enantioselectivity