Exploring oxocarbenium ion chemistry Diana Berheci, Jonathan Burton University of Oxford, UK
Oxonium and oxocarbenium ions are compounds bearing trivalent, positively charged oxygen atoms. 1 Although they are often proposed as key reactive intermediates in organic chemistry reactions and natural product biosynthesis, 2–4 their chemistry is still underexplored. As part of our ongoing efforts in synthesis and characterisation of oxonium ions, we investigated the formation of oxonium ions such as 2 from acyclic substrates. However, this underwent a previously unreported rearrangement into oxocarbenium ion 3 , which gives enone 4 upon a nucleophilic quench. 5 This project focuses on understanding the mechanism, scope and utility of this novel transformation, which we have described as a Friedel-Crafts Pinacol Rearrangement. We present our optimised, metal-free variation of this reaction, which we were able to expand to a wide range of functional groups, demonstrating the versatility of this methodology. We also outline our mechanistic hypothesis for this transformation, supported by NMR studies. References 1. Olah, G. A. Onium Ions ; Wiley: New York ; Chichester, 1998. 2. Hicks, H. B.; Brown, D. S.; Sam Chan, H. S.; Sousa, B. A.; Christensen, K. E.; Burton, J. W. Total Synthesis and Structure Confirmation of (E) and (Z)-Ocellenyne. Org Lett 2022 , 24 (50), 9174–9178. https://doi.org/10.1021/acs.orglett.2c03524. 3. Sam Chan, H. S.; Nguyen, Q. N. N.; Paton, R. S.; Burton, J. W. Synthesis, Characterization, and Reactivity of Complex Tricyclic Oxonium Ions, Proposed Intermediates in Natural Product Biosynthesis. J Am Chem Soc 2019 , 141 (40), 15951– 15962. https://doi.org/10.1021/jacs.9b07438. 4. Chan, H. S. S.; Thompson, A. L.; Christensen, K. E.; Burton, J. W. Forwards and Backwards – Synthesis of Laurencia Natural Products Using a Biomimetic and Retrobiomimetic Strategy Incorporating Structural Reassignment of Laurefurenynes C–F. Chem Sci 2020 , 11 (42), 11592–11600. https://doi.org/10.1039/D0SC04120C. 5. Chan, H. S. S.; Burton, J. W. Unpublished Results .
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