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Title: Part I : Tungsten-catalyzed cyclization of alkyne derivatives ; Part II : Palladium-catalyzed C-H bond functionalization of benzylic phosphonic monoesters
Authors: Meng, Xiangjian
Keywords: DRNTU::Science
Issue Date: 2013
Source: Meng, X. (2013). Part I : Tungsten-catalyzed cyclization of alkyne derivatives ; Part II : Palladium-catalyzed C-H bond functionalization of benzylic phosphonic monoesters. Doctoral thesis, Nanyang Technological University, Singapore.
Abstract: The work of this thesis has been directed towards the development of tungsten-catalyzed chemistry in the transformation of alkyne derivatives, and palladium-catalyzed functionalization of benzylic phosphonic monoesters via C−H activations. This thesis is divided into two parts:  Part I is aimed at exploring novel approaches for the synthesis of heterocycles via cylization of alkyne derivatives employing tungsten catalysis. Chapter 1 gives an introduction to tungsten catalysis and its application in the formation of heterocycles via cyclization of alkyne derivatives. Chapter 2 describes the tungsten-catalyzed cyclization of N-propargylic amides to afford the corresponding oxazolines or oxazines via 5-exo-dig or 6-endo-dig mode. Chapter 3 details the tungsten-catalyzed cyclization of α-alkynyl-β-keto acids, keto esters, and diketones to afford methylenelactones, furans, and methylenecyclopentanes via 5-exo-dig cyclization under photo conditions. Also, the present approach could be further applied to 5-endo-dig cyclization. In addition, pyrroles, pyridines and isoquinolines were also efficiently synthesized via cyclization of alkyne derivatives tethered to nitrogen nucleophiles under thermal conditions in the presence of tungsten catalysis.  Part II is aimed at exploring phosphoryl-related directing groups-assisted C−H activation reactions employing palladium catalysis. Chapter 4 gives an introduction of palladium-catalyzed directing-group-assisted olefination and arylation of aryl C−H bonds in recent decades and a brief discussion of related mechanisms. In Chapter 5, the new monophosphonic acid directing group was successfully utilized in the Pd(II)-catalyzed ortho-olefination and acetoxylation of benzylic phosphonic monoesters. The synthetic utility of ortho-olefination was vi exemplified by the application of the newly formed olefinated products in Horner-Wadsworth-Emmons reactions. In Chapter 6, the new mono-phosphonic acid-directing group was successfully utilized in the Pd(II)-catalyzed ortho-arylation of benzylic phosphonic monoesters with potassium aryltrifluoroborates. A wide range of benzylic phosphonic monoesters underwent clean ortho-arylation in high yields and excellent functional group tolerance was also observed. The newly formed arylated products were also successfully applied in Horner-Wadsworth-Emmons reactions. The success of the work in Chapter 4 and 5 offers further development of other phosphoryl-related directing groups in the transition-metal-catalyzed C−H activations.
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