A Photocatalyzed Synthesis of Naphthalenes by Using Aniline as a Traceless Directing Group in [4 + 2] Annulation of Amino-benzocyclobutenes with Alkynes

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Amino-benzocyclobutenes, Annulation, C-C cleavage, Photocatalysis, Substituted naphthalenes


We report a visible-light-promoted synthesis of substituted naphthalenes via [4 + 2] annulation of amino-benzocyclobutenes with alkynes. Amino-benzocyclobutenes, which are conveniently synthesized by [2 + 2] cycloaddition of arynes with ketenes followed by reductive amination, undergo regioselective opening of the cyclobutenyl ring to reveal a presumably distonic radical cation upon photooxidation by an excited iridium complex. The distonic radical cation undergoes the annulation with terminal and internal alkynes as well as diynes to afford structurally diverse naphthalenes. The regiochemistry of the annulation follows the pattern displayed in the addition of nucleophilic carbon radicals to alkynes. The aniline group plays a dual role in which it not only directs the initial photooxidation to generate the amine radical cation but also serves as a leaving group to complete aromatization.


Principal Investigator: Nan Zheng

Acknowledgements: We thank the University of Arkansas, the Arkansas Bioscience Institute, the National Institutes of Health (NIH) (grant number P30 GM103450) from the National Institute of General Medical Sciences, and NSF Career Award (Award Number CHE-1255539) for generous support of this research.

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