Theoretical Studies on the Regioselectivity of Iridium-Catalyzed 1,3-Dipolar Azide鈥揂lkyne Cycloaddition Reactions

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• 作者：Qiong Luo ; Guochen Jia ; Jianwei Sun ; Zhenyang Lin
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：December 19, 2014
• 年：2014
• 卷：79
• 期：24
• 页码：11970-11980
• 全文大小：776K
• ISSN：1520-6904

文摘

Iridium-catalyzed cycloaddition of thioalkynes and bromoalkynes with azides have been investigated with the aid of density functional theory (DFT) calculations at the M06 level of theory. Our investigation focused on the different regioselectivity observed for the reactions of the two classes of alkynes. The DFT results have shown that the mechanisms of cycloaddition reactions using thioalkynes and bromoalkynes as substrates are similar yet different. The reactions of thioalkynes occur via a metallabicyclic Ir鈥揷arbene intermediate formed through alkyne鈥揳zide oxidative coupling via attack of the azide terminal nitrogen toward the 尾 alkyne carbon, whose carbene ligand is stabilized by an alkylthio/arylthio substituent. Reductive elimination from the intermediate leads to the formation of the experimentally observed 5-sulfenyltriazole. In the reactions of bromoalkynes RC鈮Br, the reaction mechanism involves the initial formation of a six-membered-ring metallacycle intermediate in the oxidative coupling step. The six-membered-ring intermediate then undergoes isomerization via migrating the terminal azide nitrogen from the 尾 carbon to the 伪 carbon to form a much less stable metallabicyclic Ir鈥揷arbene species from which reductive elimination gives 4-bromotriazole.