Small-sized N-heterocycles are important structures in organic synthesis and medicinal chemistry. Palladium-catalysed intramolecular aminations of the C−H bonds of unfunctionalized amine precursors have recently emerged as an attractive new method for N-heterocycle synthesis. However, the way to control the reactivity of high-valent Pd intermediates to form the desired C−N cyclized products selectively remains poorly addressed. Herein we report a strategy to control the reductive elimination (RE) pathways in high-valent Pd catalysis and apply this strategy to achieve the synthesis of highly strained four-membered benzazetidines via the Pd-catalysed intramolecular C−H amination of N-benzyl picolinamides. These reactions represent the first practical synthetic method for benzazetidines and enable access to a range of complex benzazetidines from easily obtainable starting materials. The use of a newly designed phenyliodonium dimethylmalonate reagent is critical, as oxidation of Pd(II) palladacycles with this reagent favours a kinetically controlled C−N RE pathway to give strained ring-closed products.
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G.C. thanks the State Key Laboratory of Elemento-Organic Chemistry at Nankai University and the Pennsylvania State University for financial support for the experimental part of this work. P.L. thanks the University of Pittsburgh for financial support for the computational part of the work. Calculations were performed at the Center for Simulation and Modeling at the University of Pittsburgh and the Extreme Science and Engineering Discovery Environment (XSEDE) supported by the National Science Foundation.
The authors declare no competing financial interests.
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He, G., Lu, G., Guo, Z. et al. Benzazetidine synthesis via palladium-catalysed intramolecular C−H amination. Nature Chem 8, 1131–1136 (2016). https://doi.org/10.1038/nchem.2585
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