UBC Theses and Dissertations
Strategies towards carbon-carbon bond formation via tandem hydrothiolation/Kumada cross-coupling Sabarre, Anthony
Using recently developed methodology from our group, a variety of aryl and aliphatic terminal alkynes were reacted with n-propanethiol to undergo catalytic alkyne hydrothiolation in the presence Tp*Rh(PPh₃)₂ The alkynes examined afforded the branched isomer with high regioselectivity and moderate-to-high yield. Unsubstituted aryl alkynes, or those containing an electron-donating substituent at the para position, gave the branched vinyl sulfide in good isolated yield. In contrast, vinyl sulfides derived from aryl alkynes containing an electron-withdrawing substituent at the para position showed a decrease in reactivity and yield. The aliphatic alkynes that were investigated gave the desired branched vinyl sulfide in good yield. The isolated vinyl sulfides were then subjected to Kumada cross-coupling in the presence of NiCl₂(PPh₃)₂ with various aryl and aliphatic Grignard reagents, affording the corresponding 1,1 -disubstituted olefins. While benzyl-, phenyl- and trimethylsilylmagnesium halides were shown to be suitable cross-coupling partners, phenylethynyl-, vinyl- and n-butylmagnesium halides were not. Once the viability for the Kumada cross-coupling of vinyl sulfides was established, a one-pot protocol was investigated. It was shown that the one-pot procedure afforded the desired 1,1 -disubstituted olefin from readily available terminal alkynes in similar, and in some cases superior, yields than the two-step process.
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