Catalytic Synthesis with Titanium and Carbenes.

The lecture will focus on two research activities of our group: (i) development of novel N-heterocyclic carbenes/azolium salts for catalytic Umpolung reactions, and (ii) development of Ti-salalen catalysts for asymmetric epoxidations with hydrogen peroxide. 
Ad (i): Based on our experience in the first preparation and characterization of Breslow-intermediates,1 we have recently been able to design and synthesize a new generation of carbene organocatalysts2 which promote hitherto impossible catalytic transformations in-volving diamino dienols and azolium enolates, such as the one-step conversion of 9-oxocitral to nepetalactone shown below (Scheme, left). First applications of these novel N-hetero-cyclic carbenes as ligands in Co-catalyzed C-H activation will briefly be presented as well.3 
Ad (ii): The most recent generation of cis-DACH derived salalen-ligands shown in the Scheme (right) allows the efficient and highly enantioselective epoxidation of terminal, non-conjugated olefins with hydrogen peroxide.4 Several examples and mechanistic aspects of this process will be presented. Professor Berkessel

References:

  1. a) A. Berkessel, S. Elfert, V. R. Yatham, J.-M. Neudörfl, N. E. Schlörer, J. H. Teles, Angew. Chem. Int. Ed. 2012, 51, 12370; b) A. Berkessel, V. R. Yatham, S. Elfert, J.-M. Neudörfl, Angew. Chem. Int. Ed. 2013, 52, 11158; c) M. Paul, M. Breugst, J.-M. Neudörfl, R. B. Sunoj, A. Berkessel, J. Am. Chem. Soc. 2016, 138, 5044; d) M. Paul, P. Sudkaow, A. Wessels, N. E. Schlörer, J.-M. Neudörfl, A. Berkessel, Angew. Chem. Int. Ed. 2018, 57, 8310-8315.
  2. V. R. Yatham, W. Harnying, D. Kootz, J.-M. Neudörfl, N. E. Schlörer, A. Berkessel, J. Am. Chem. Soc. 2016, 138, 2670.
  3. N. Sauermann, J. Loup, D. Kootz, V. R. Yatham, A. Berkessel, L. Ackermann, Synthesis, 2017, 49, 3476.
  4. a) A. Berkessel, M. Lansing, H. Engler, T. M. Leuther, J. M. Neudörfl, ChemCatChem, 2016, 8, 3706; b) Q. Wang, J.-M. Neudörfl, A. Berkessel, Chem. Eur. J., 2015, 21, 247; c) A. Berkessel, T.
  5. Günther, Q. Wang, J.-M. Neudörfl, Angew. Chem. Int. Ed. 2013, 52, 8467.