Propargylic Dialkyl Effect for Cyclobutene Formation through Ir(III)-Catalyzed Cycloisomerization of 1,6-Enynes
Xuanyu Zhu1, Yi Li1, Hongtao Luo1
1Shanghai Frontiers Science Center of Biomimetic Catalysis, Joint Laboratory of International Cooperation of Resource Chemistry of Ministry of Education, Shanghai Normal University, Shanghai 200234, China.
Abstract:
The propargylic dialkyl effect (PDAE) has a significant impact on the cyclization reaction of enynes, partly reflected in changing the types of products. Herein, we described the influence of the propargylic dialkyl effect on the Ir(III)-catalyzed cycloisomerization of 1,6-enynes to provide strained cyclobutenes. A series of substituted 1,6-enynes were proved to be excellent substrate candidates in the presence of [Cp*IrCl2]2 in toluene. Mechanistic investigation, based on deuterium labeling experiments and control experiments, indicated that the propargylic dialkyl effect might boost C(sp)-H activation by preventing the coordination of active iridium species to the C(sp)≡C(sp) bond of enynes. This finding contributes to the fundamental understanding of enyne cyclization reactions and offers valuable insight into the propargylic dialkyl effect.
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