Please use this identifier to cite or link to this item:
Title: Development of new reactions and reagents in carbene-catalyzed addition of carbon and nitrogen nucleophiles to unsaturated acyl azolium intermediates
Authors: Wu, Xingxing
Keywords: DRNTU::Science::Chemistry
Issue Date: 2017
Source: Wu, X. (2017). Development of new reactions and reagents in carbene-catalyzed addition of carbon and nitrogen nucleophiles to unsaturated acyl azolium intermediates. Doctoral thesis, Nanyang Technological University, Singapore.
Abstract: This thesis focuses on development of efficient protocols for access to advanced complex molecules enabled by N-heterocyclic carbene (NHC) catalyzed LUMO activation of enal or its ester derivatives, and discovery of polyhalide as simple organic oxidant for oxidative carbene catalysis. It contains five parts: Chapter 1 first gives a brief introduction to the history of asymmetric organocatalysis, followed by development of N-heterocyclic carbene (NHC) catalysis. This includes three main aspects, (a) catalysis involving umpolung acyl-anion, (b) homoenolate catalysis, (c) reactions involving acyl azolium intermediates. This chapter also illustrates the challenges and opportunities in NHC catalyzed reactions, especially in heteroatoms as nucleophiles for α, β-unsaturated acyl azolium and simple oxidants for oxidative NHC catalysis. Chapter 2 describes a single-step, organocatalytic and enantioselective cascade process for access to a multi-cyclic lactone that constitutes the core structure of iridoids. This protocol shows the synthetic power of a NHC catalyst for the activation of a readily available and stable carboxylic ester to give the unsaturated acyl azolium intermediate. Chapter 3 demonstrates an efficient protocol for the preparation of pyrazolidinone products via nucleophilic β-carbon amination of enals under oxidative NHC catalysis. The heterocycle adducts from the catalytic reaction can readily undergo further transformations to afford various useful functional molecules, such as pyrazolidines and β-amino acid derivatives. Chapter 4 shows a novel and efficient cascade approach for the direct assembly of two privileged scaffolds (pyrrolidine and β-lactone) with good to excellent yield and enantioselectivity. This study sheds light on modulating the reactivity of nitrogen atom for challenging NHC-catalyzed asymmetric C-N bond formations. Chapter 5 introduces polyhalide reagents as simple and inexpensive oxidants for oxidative NHC catalysis, providing efficient methods for functionalization of the α, β and γ atoms of aldehydes. The oxidative process involves multiple radical intermediates, and shall inspire new reaction development via NHC-catalyzed radical process.
DOI: 10.32657/10356/72774
Fulltext Permission: open
Fulltext Availability: With Fulltext
Appears in Collections:SPMS Theses

Files in This Item:
File Description SizeFormat 
Wu Xingxing thesis.pdfMain article Wu Xingxing PhD thesis7.6 MBAdobe PDFThumbnail

Page view(s)

Updated on Jan 24, 2021

Download(s) 50

Updated on Jan 24, 2021

Google ScholarTM




Items in DR-NTU are protected by copyright, with all rights reserved, unless otherwise indicated.