School of Natural and Environmental Sciences

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Understanding product chemoselectivity in organocatalysis by carbenes

Chemistry Seminar Series - Dr AnnMarie O’Donoghue, Durham University

Date/Time: Tuesday 11 December 2018, 14:00 to 15:00

Venue: Room 2.76, Bedson Building

Despite many conceptual synthetic advances in organocatalysis by N-heterocyclic carbenes (NHCs), it is not understood why product distributions often differ dramatically with catalyst scaffold or with subtle substituent variation within a catalyst family.1

In particular, a variety of chemo- and stereoselective reaction types are known for the archetypal acyl anion mode of NHC-reactivity, with a generally accepted mechanism shown in Fig. 1.

Comparatively small changes in structure, e.g. variation of fused ring size (n = 1-3) can dramatically alter the product outcome.

In the first part of the seminar, our recent mechanistic and kinetic studies of the impact of the fused ring size in 1 will be reported.

First isolated by Bertrand in 2006,2 bis(amino)cyclopropenylidenes (BACS) 2 are promising as organocatalysts for acyl anion and extended umpolung reactions showing orthogonal chemoselectivity to N-heterocyclic carbenes (NHCs).

Typically generated in situ from cyclopropenium precursors 3, BACS 2 (R = Et) efficiently promote the Stetter reaction with minimal contribution from a competing benzoin reaction even with more ‘difficult’ Stetter acceptors such as β-alkyl substituted-(α,β-unsaturated)-ketone acceptors.3

In the second part of the seminar, our recent mechanistic and kinetic results on the origins of the orthogonal reactivities of BACs 2 and NHCs 1 will be presented.

References

  1. D. M. Flanigan, F. Romanov-Michailidis, N. A. White and T. Rovis, Chem. Rev., 2015, 115, 9307-9387
  2. V. Lavallo, Y. Canac, B. Donnadieu, W. W. Schoeller and G. Bertrand, Science, 2006, 312, 722
  3. M. M. D. Wilde and M. Gravel, Angew. Chem. Int. Ed., 2013, 52, 12651
Fig. 1 and 2 and 3.
Fig. 1, 2 and 3