title: Access to α-Arylglycines by Umpolung Carboxylation of Aromatic Imines with Carbon Dioxide.
abstract: A straightforward and transition-metal-free approach for the efficient synthesis of α-arylglycine derivatives from aromatic imines and carbon dioxide was enabled by an umpolung carboxylation reaction. Various substituted diphenylmethimines underwent the carboxylation smoothly with carbon dioxide in the presence of potassium tert-butoxide and 18-crown-6 to give the corresponding carboxylated products in good to high yields. Besides the enhancement of the solubility of potassium tert-butoxide in THF, 18-crown-6 also plays key roles in suppressing the reverse protonation or 1, 3-proton shift isomerization as well as by stabilizing the carboxylated intermediate.
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, China.
authors.forename: Chun-Xiao
authors.initials: CX
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, China.
authors.forename: Wen-Zhen
authors.initials: WZ
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116024, China.
authors.forename: Xiao-Bing
authors.initials: XB
authors.lastname: Lu
keywords: amino acids; carbon dioxide fixation; carboxylation; transition-metal-free synthesis; umpolung