Functionalization of alkynes is a very important field in organic chemistry, because it provides straightforward synthesis of multi-substituted alkenes, which are widely present in biological compounds, natural products, and pharmaceuticals. However, despite the significant progress made in the past few decades, there still remain challenges (e.g., regio- and stereocontrol), particularly for unsymmetrical internal alkynes in intermolecular reactions under mild conditions. Moreover, previous studies on this topic have been focused on electron-normal and electron-deficient alkynes. In contrast, the simple, mild, highly regio- and stereoselective functionalization of electron-rich alkynes (bearing an electron-donating group (EDG) at the triple bond) remains underdeveloped.

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Functionalization of alkynes is a very important field in organic chemistry, because it provides straightforward synthesis of multi-substituted alkenes, which are widely present in biological compounds, natural products, and pharmaceuticals. However, despite the significant progress made in the past few decades, there still remain challenges (e.g., regio- and stereocontrol), particularly for unsymmetrical internal alkynes in intermolecular reactions under mild conditions. Moreover, previous studies on this topic have been focused on electron-normal and electron-deficient alkynes. In contrast, the simple, mild, highly regio- and stereoselective functionalization of electron-rich alkynes (bearing an electron-donating group (EDG) at the triple bond) remains underdeveloped.

In Chapter 1, Ir-catalyzed highly α regioselective hydroboration and dihydroboration of internal thioalkynes with hydroborane under mild conditions has been developed. Excellent control over mono- and dihydroboration can be achieved by changing the equivalence of the hydroborane employed.

Chapter 2 describes an efficient divergent method for Rh-catalyzed β syn hydrosilylation and HNTf₂-catalyzed β trans hydrosilylation of internal ynamides with high regio- and stereoselectivity for the first time. The reactions feature simple operation under mild reaction conditions. In addition, some useful modifications to the obtained products have been realized successfully.

Chater 3 introduces an efficient and simple method of TMSCN anti addition of ynamides with excellent selectivity, in the presence of catalytic HNTf₂. Several control experiments revealed that the actual catalyst for this process is TMSNTf₂, which is formed in situ from TMSCN and HNTf₂. The reactions has a wide substrate scope. Some related product derivatizations have also been carried out to demonstrate the utility of the efficient process.

In Chapter 4, anti addition of TMSPPh₂ to ynamides with excellent selectivity is disclosed. Similar to TMSCN addition, this process is also catalyzed by HNTf₂ under mild conditions. It also enjoys wide substrate scope and high efficiency. The alkynes can also be extended to thioalkynes and ynol ethers to achieve excellent anti selectivity. Furthermore, controlled experiments revealed that the actual catalyst is TMSNTf₂, which is formed in situ from TMSPPh₂ and HNTf₂.

Next, interesting ligand-controlled divergent syn hydroarylation, anti hydroiodination, and anti-hydrosilylation of internal ynamides are developed, as described in Chapter 5. Controlled experiments were carried out to reveal that the electronic and steric effect of the ligand greatly influence the excellent selectivity of syn hydroarylation and anti hydrosilylation.

Finally, Chapter 6 describes the first metal-free trimolecular [2+2+2] cycloaddition of internal alkynes and nitriles for de novo synthesis of fully-substituted pyridines. With the versatile Brønsted acid catalyst HNTf₂, a range of internal ynamides and unactivated nitriles smoothly participated in the intermolecular cyclotrimerization not only under mild conditions, but also with complementary chemoselectivity and excellent regioselectivity. Particularly remarkable is the smooth acid catalyst turn-over in the presence of the basic pyridine product.