Regio‐ and Diastereoselective Formal [2+2] Cycloaddition of Allenes with Amino‐Functionalized Alkenes by Rare‐Earth‐Catalyzed C(sp2)−H Activation

• Published in: Angewandte Chemie International Edition 2022-11, Vol.61 (45), p.e202210624-n/a
• Main Authors: Xu, Wenxuan, Cong, Xuefeng, An, Kun, Lou, Shao‐Jie, Li, Zhenghua, Nishiura, Masayoshi, Murahashi, Tetsuro, Hou, Zhaomin
• Format: Article
• Language: English
• Subjects: Alkenes; Allene; Allenes; C(sp2)−H Activation; Catalysts; Cycloaddition; Cyclobutane; Cyclobutanes; Earth; Rare species; Rare-Earth Catalysts; Stereoselectivity
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202210624

The [2+2] cycloaddition of allenes with alkenes is of much interest and importance as a straightforward route for the construction of four‐membered carbocycles but has remained much underexplored to date. Herein we report for the first time the intermolecular regio‐ and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino‐functionalized alkenes by half‐sandwich rare‐earth catalysts. The reaction proceeded through an allene C(sp2)−H activation mechanism initiated by the site‐selective deprotonation of the allene unit by a rare‐earth metal alkyl species followed by alkene insertion into the resulting metal‐allenyl bond and the subsequent intramolecular cycloaddition to an allene C=C bond. This protocol offers a unique route for the synthesis of a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously. Half‐sandwich rare‐earth catalysts serve as a unique platform for the regio‐ and diastereoselective formal [2+2] cycloaddition of a wide range of allenes with amino‐functionalized alkenes via allene C(sp2)−H activation, affording a new family of cyclobutane and cyclobutene derivatives which were difficult to access previously.