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Current Organic Chemistry

Author(s): Hiroyuki Kawafuchi*, Lijian Ma, Md Imran Hossain and Tsutomu Inokuchi

DOI: 10.2174/1385272823666191019102511

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O-AcylTEMPOs, a Modified and Fundamental, but Unexplored Carboxylic Derivative: Recent Progress in Synthetic Applications

Page: [2102 - 2121] Pages: 20

  • * (Excluding Mailing and Handling)

Abstract

O-Acylated 2,2,6,6-tetramethylpiperidine-N-oxyls (abbr. O-AcylTEMPOs) are easily available and stable carboxylic derivatives, but their utility in organic synthesis is unexplored in contrast to analogues, such as the N-methoxy-N-methylamides, known as Weinreb amides. Especially, the O–N unit of the O-acylTEMPOs dictates a fairly electronwithdrawing character for the carbonyl function. This enhances the reactivity and stability of the resulting enolate ions. Accordingly, O-acylTEMPOs allow various transformations and this review encompasses seven topics: (1) Reactivity of O-acylTEMPOs towards nucleophiles and chemoselective transformations, (2) Reactivity of anionic species derived from O-acylTEMPOs, (3) E-Selective Knoevenagel condensation of acetoacetylTEMPOs and synthesis of furans, (4) Electrocyclization of 2,4-dienones derived from acetoacetic derivatives and 2-substituted enals, (5) Diastereoselective addition of amide anion to O-(2-alkenoyl)TEMPOs and β-amino acid synthesis, (6) Thermolysis of O-acylTEMPOs, and (7) Applications for Umpolung reactions using O-benzoylTEMPOs, useful for the electrophilic amination of alkenes and alkynes.

Keywords: O-AcylTEMPO, E-Selective Knoevenagel reaction, ester-protecting group, carboxy-aldehyde conversion, diastereoselective amide addition, β-Amino acid, amination.

Graphical Abstract

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