Transition Metal-Catalyzed Alkyne Activation Comprising Cycloisomerization, Hydrative Carbocyclizaton and Oxidative Cleavage Reaction

Abstract

ABSTRACT Transition metal-catalyzed cycloisomerization, hydrative carbocyclization and oxidative- cleavage of appropriately functionalized organic molecules are described in this dissertation. For sake of convenience and better understanding, the thesis is divided into five chapters. In the first chapter a new metal-catalyzed 6-endo-dig cyclization of 1-(2-(2-methylprop-1-enyl)phenyl)prop-2-yn-1-ol has been described, which produces substituted naphthalene derivatives with structural reorganization. In this process, we observed a 1,3-alkylidene migration via cleavage of the olefin double bond of the starting substrates. The ease and reliability of this cyclization were manifested by its compatibility with a wide diverse substrates and π-alkyne activators including PtCl2, Zn(OTf)2, AuCl and AuCl3. The second chapter deals with a novel hydrative cyclization of triynes to afford bicyclic spiro alcohols, which undergo subsequent dehydration to give bicyclic ketones. This platinum catalysis has proposed to comprise a sequence of cascade reactions including, two selective hydrations, alkyne insertion and aldol condensations. The third chapter describes, one-pot syntheses of chrysene derivatives via PtCl2-catalyzed hydrative dimerization of readily available 2-alkynyl-1-acetylbenzenes. This new tandem catalysis comprises an initial selective hydration of the alkyne, followed by chemoselective dimerization of diketone intermediates. The mechanism of this cyclization has been elucidated by 13C-labeling experiments as well as isolation of reaction intermediates. The fourth chapter presents a unique synthesis of benzopyrones and tricyclic spiroketones from hydrative carbocyclization of oxodiyne substrates catalyzed by PtCl2 and PPh3AuCl/AgOTf, respectively. These distinct carbocyclizations with Pt and Au catalysts stem from their altered regioselectivity in the oxo-assisted hydration of the neighboring alkyne carbons. The last chapter discusses a gold-catalyzed oxidative cleavage of aryl-substituted alkynyl ethers using molecular oxygen under ambient conditions; the transformation involves a remarkable cleavage of C-H, C-C and C≡C bonds simultaneous.