Gold-Catalyzed Intermolecular Annulation to Access Heterocyclic Compounds

Abstract

In chapter 2, the gold-catalyzed C-H annulation of anthranil derivatives with alkynes offers a facile, flexible, and atom-economical one-step route to unprotected 7-acylindoles. An intermediate a-imino gold carbene, generated by an intermolecular reaction, promotes ortho-aryl C-H functionalization to afford the target products. The transformation proceeds with a broad range of substrates under mild conditions. Moreover, the obtained functionalized indole products represent a versatile platform for the construction of diverse indolyl frameworks. In chapter 3, a gold-catalyzed cascade annulation of propargylic silyl ethers with anthranils proceeds through a sequential ring opening/1,2-H-shift/protodeauration/Mukaiyama aldol cyclization. This method offers a regiospecific and modular access to 2-aminoquinolines and other quinoline derivatives under mild conditions and with a broad functional-group tolerance. The conversion is possible on a gram scale, which underlines the synthetic practicability of this methodology. The versatility of the obtained scaffold has been demonstrated by useful postfunctionalization. In chapter 4, gold and platinum-catalyzed counteranion-directed divergent [4+2] annulations have been described, enabling the convergent assembly of densely substituted quinoxaline and quinoxaline N-oxide from benzofurazans and ynamides. A broad scope of functional groups was well tolerated, delivering high regioselectivity. The quinoxaline N-oxides were suitable for the further C-H functionalization. Mechanism studies suggested the counteranion-tuned distinct cyclization pathways toward the corresponding product. In chapter 5, the gold-catalyzed oxidative [2+2+1] annulation of two molecules of ynamide with 2, 3-quinoxaline N-oxide, enables the facile and convergent assembly of fully-substituted symmetric and unsymmetric furan frameworks. A wide range of functional groups is well compatible due to the mild condition. The strategy works also for the intramolecular macrocyclization of di-ynamides for the synthesis of macrocyclic furan derivatives.