Regio- and stereoselective functionalization of internal alkynes : hydrosilylation and azide-alkyne cycloaddition

Abstract

Chapter l summarizes the development in regioselective synthesis of vinyl silanes and fully substituted triazoles from unsymmetrical internal alkynes, on which my PhD research is mainly focused. In Chaper 2, the first highly efficient ligand-controlled regio- and stereodivergent intermolecular hydrosilylation of internal alkynes is disclosed. The cationic ruthenium complexes [Cp*Ru(MeCN)₃]⁺ and [CpRu(MeCN))₃]⁺ have been demonstrated to catalyze hydrosilylations of silyl alkynes to form a range of vinyldisilanes with excellent but opposite regio- and stereoselectivity, with the former being α anti addition and the latter β syn addition. Theoretical studies combined with experimental evidence confirm that steric effect plays a critical role in governing the regio- and stereoselectivity, and the interplay between the substituent in the alkyne ( e.g., silyl group) and the ligand ultimately determines the observed remarkable regio- and stereodivergence. Described in Chapter 3 is the utilization of the cationic ruthenium complex [Cp*Ru(MeCN)₃]PF₆, for the extension to the hydrosilylation of electron-rich alkynes. With a proper select of silane, various 1-thiovinylsilanes were afforded with high regio- and stereoselectivity. Specifically, this syn-addition process is an important complement to the know processes. Related derivatizations of the product were carried out to demonstrate the utility of this process. We have demonstrated the first Ir-catalyzed hydrosilylation of 1-thioalkynes to provide a variety of 1-thiovinylsilanes with high regio- and stereoselectivities as well. Various 1-thioalkynes and silanes were suitable in this mild process. Related derivatizations of the product were carried out to demonstrate the utility of this process. In Chapter 4, an iridium-catalyzed azide-alkyne cycloaddition reaction (lrAAC) of electron-rich internal alkynes is described. It is the first efficient intermolecular AAC of internal thioalkynes. The reaction exhibits remarkable features, such as high efficiency and regioselectivity, mild reaction conditions, easy operation, and excellent compatibility with air and a broad spectrum of oganic and aqueous solvents. It complements the well-known CuAAC and RuAAC click reactions.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology