Catalytic enantioselective 6π photocyclization of acrylanilides Pearse Solon 1 , Benjamin Jones 1 , Mihai Popescu 1,2 , Jiyuan Du 1 , Robert Paton 2 , Martin Smith 1 1 University of Oxford, UK, 2 Colorado State University, USA Controlling absolute stereochemistry in photochemical reactions is challenging due to high rates of background reactivity stemming from low excited state activation barriers. Successful strategies generally rely on selective excitation of the reaction substrate in a chiral environment. 1 Recent studies have demonstrated that chiral Lewis acids can mediate energy transfer from a photosensitizer to enable dual catalytic enantioselective triplet state reactions. 2-4
Here, we apply this approach to the enantioselective catalysis of a [6π] photocyclization; a reaction class that until now has not been amenable to asymmetric catalysis. High enantioselectivity was made possible by the design of a novel homoleptic iridium photosensitizer optimized to undergo energy transfer to the reaction substrate only in the presence of a chiral Lewis acid. The enantioselectivity of the process depended not just on the triplet energy of the photosensitizer, with neutral iridium complexes outperforming cationic complexes with similar triplet energies. The results presented here demonstrate that photocatalyst tuning can offer a means to suppress background reactivity and improve enantioselectivity in photoreactions where chiral Lewis acids give rise to only small changes in triplet energy. 5 References 1. Johannes Großkopf, Thilo Kratz, Thomas Rigotti, and Thorsten Bach, Chem. Rev. 2022, 122, 2, 1626–1653 2. Travis R. Blum, Zachary D. Miller, Desiree M. Bates, Ilia A. Guzei, Tehshik P. Yoon, Science, 2016, 354, 1391 3. Juana Du, Kazimer L. Skubi, Danielle M. Schultz, Tehshik P. Yoon, Science, 2014, 344, 6182, 392 4. R.Brimioulle, T. Bach, Science 2013, 342, 840– 8435) Benjamin A. Jones, Pearse Solon, Mihai V. Popescu, Ji-Yuan Du, Robert Paton, Martin D. Smith, ChemRxiv, 2022, DOI: 10.26434/chemrxiv-2022-dnzbk
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