UBC Theses and Dissertations
Synthesis of 1,1-disubstituted alkyl vinyl sulfides via rhodium-catalyzed alkyne hydrothiolation : scope and limitations Yang, Jun
Tp*Rh(PPh₃)₂ is a useful catalyst for alkyne hydrothiolation. Vinyl sulfides, the products of this reaction, are useful synthetic intermediates. The goal of this thesis project was to explore the scope and limitations of alkyne hydrothiolation with alkyl thiols catalyzed by Tp*Rh(PPh₃)₂ A variety of thiols and alkynes successfully undergo catalytic hydrothiolation. In general, the branched isomer was formed in good-to-excellent yields and with high selectivity. Electron rich phenylacetylenes were more reactive than electron deficient ones, and provided higher yields. Aliphatic alkynes need longer reaction times than aromatic alkynes in order to reach complete conversion. A broad range of functional groups were well tolerated, including halides, amines, nitriles, amines, ethers, esters and silanes. Alkoxy groups with the ability to coordinate with rhodium slowed down the catalytic turnover and lowered the yields. Strongly coordinating groups, such as pyridine, precluded catalysis. Alkynes that are Michael acceptors react with reversed regioselectivity. Hydrothiolation using internal alkynes was successful, although the reaction times were longer and temperatures are higher than that needed for terminal alkynes. Overall, the work presented in this thesis provides a general method in construction of branched alkyl vinyl sulfides from alkynes.
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