Modular synthesis, applications and photophysical study of novel acridinium photocatalysts Valeriia Hutskalova and Christof Sparr University of Basel, Switzerland Photoredox catalysis has experienced significant advances over the last decade to become a valuable tool for otherwise intractable transformations under mild conditions. [1] In this context, short and modular synthesis of diverse photocatalysts with different photochemical properties is an important instrument for the further development of the field. As a sustainable replacement for the precious-metal photoredox catalysts, aсridinium salts have emerged as valuable organic cationic photocatalysts due to their favorable photophysical features. [2,3] We herein describe a new short two-step route to acridinium dyes comprising aryne-imine-aryne coupling combined with subsequent oxidation. [4,5] This strategy was also applied for the preparation of a key tetrafluorinated acridinium salt which served as a linchpin intermediate for the late-stage diversification by nucleophilic aromatic substitution. Diverse acridinium derivatives were prepared with high yields using this methodology including aza- rhodols as a novel class of acridinium photocatalysts. [6] The obtained photocatalysts were successfully applied for organocatalytic C–N cross-coupling. Furthermore, the modularity of the developed synthetic strategy allowed the preparation of the acridinium derivatives with efficient intersystem crossing that were suitable for the polyarene reduction and triplet-triplet annihilation upconversion. [7]
References 1. J. M. R. Narayanam, C. R. J.Stephenson, Chem. Soc. Rev. 2011 ,40,102–113. 2. C. Fischer, C.Kerzig, B.Zilate, O. S. Wenger, C.Sparr, ACS Catal. 2020 ,10,210–215. 3. V. Hutskalova, C. Sparr, Science of Synthesis Knowledge Updates , (2022) 1, 1–44. 4. V. Hutskalova, C. Sparr, Synlett 2021 , 33, 1180–1183. 5. V. Hutskalova, C. Sparr, Helv. Chim. Acta 2021 , 104, e2100182. 6. V. Hutskalova, C. Sparr, Org. Lett. 2021 , 23, 5143–5147. 7. B. Pfund ‡ , V. Hutskalova ‡ , C. Sparr, O. S. Wenger, unpublished results . ( ‡ B. F. and V. H. contributed equally)
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