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Published on: June 21, 2017
Ruthenium-Catalyzed Intermolecular [2 + 2] Cycloaddition of Unactivated Allenes and Alkynes with Unusual
Chaoshen Zhang1, Herman H Y Sung1, Ian D Williams1
1Department of Chemistry and the Hong Kong Branch of Chinese National Engineering Research Centre for Tissue Restoration & Reconstruction, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR 999077, China.
This study introduces an efficient protocol for cycloaddition reactions using a CpRu catalyst, yielding diverse cyclobutenes with unexpected regioselectivity. The findings offer new synthetic routes and mechanistic insights into these important chemical transformations.
Area of Science:
- Organic Chemistry
- Catalysis
- Cycloaddition Reactions
Background:
- Intermolecular [2+2] cycloadditions are crucial for synthesizing cyclic compounds.
- Controlling regioselectivity in cycloadditions of unactivated allenes and alkynes remains challenging.
Purpose of the Study:
- To develop an efficient protocol for intermolecular [2+2] cycloaddition of unactivated and unsymmetrical allenes and alkynes.
- To achieve unusual regioselectivity, favoring the most hindered isomer.
- To explore the scope and functional group compatibility of the reaction.
Main Methods:
- Utilized CpRu(MeCN)3PF6 as a catalyst for the cycloaddition reaction.
- Employed a combination of experimental studies and Density Functional Theory (DFT) calculations.
- Investigated the reaction mechanism and regioselectivity.
Main Results:
- Developed an efficient protocol for [2+2] cycloaddition of allenes and alkynes.
- Achieved counterintuitive regioselectivity, favoring the sterically hindered isomer.
- Synthesized a diverse range of 3-alkylidenecyclobutenes with broad scope and good functional group tolerance.
Conclusions:
- CpRu(MeCN)3PF6 is a uniquely effective catalyst for this transformation.
- The developed protocol offers a novel synthetic pathway to substituted cyclobutenes.
- Experimental and DFT studies elucidated the mechanism and the origin of the unusual regioselectivity.
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