Transition Metal Catalyzed Functionalization of Alkynes

Abstract

Alkynes are important building blocks of chemistry. Here we have described four new transition metal catalyzed transformations of alkynes. These transformations generate new C–C σ bonds that are fundamental in organic synthesis. The first is a copper-catalyzed anti-Markovnikov hydroallylation of alkynes. This reaction generates 1,4 or skipped dienes and makes use in-situ generated copper hydride intermediate to achieve high E-selectivity. Unsymmetrical internal alkynes were also utilized in this method. Selectivity was achieved through inductive polarization of the triple bond by placing an electron withdrawing heteroatoms at the propargyl position of the alkyne. Following this, the development of a photoinduced copper-catalyzed alkylation of terminal alkynes with alkyl iodides is discussed. The reaction proceeds though copper acetylide intermediate which is activated by blue light that facilitates the desired coupling. It provides access to challenging dialkyl internal alkynes and serves as an alternative to the challenging Sonogashira coupling. Key to the success of the reaction was the use of terpyridine ligand to suppress the undesired light-promoted polymerization of the starting material. In the third chapter, a new method of hydroalkylation of terminal alkynes is described that generates disubstituted E-alkenes. The reaction makes use of a copper catalysts and a nickel co-catalyst to couple terminal alkynes and alkyl iodides. Such use of alkyl iodides expands the scope of hydroalkylation method Mechanistic study reveals that copper catalyst is responsible for the high selectivity of the transformation, whereas nickel catalysts promote the important cross-coupling step with alkyl iodide. Finally, the fourth chapter describes a new hydroalkylation reaction that generates E-alkenyl carbonyl species. The reaction is achieved via copper hydride addition to alkynes followed by the coupling of α-bromocarbonyls. Mechanistic study reveals a single electron transfer process is responsible for the desired cross coupling of alkenylcopper intermediate.