Communication
Organic & Biomolecular Chemistry
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3 S. Díez-González, N. Marion and S. P. Nolan, Chem. Rev.,
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Fig. 1 Pseudo-stereochemical ligands 12a and 17c.
5 Selected examples: (a) D. Enders, H. Gielen, G. Raabe,
J. Runsink and J. H. Teles, Chem. Ber., 1996, 129, 1483;
(b) W. A. Herrmann, L. J. Goossen, C. Köcher and
G. R. J. Artus, Angew. Chem., Int. Ed. Engl., 1996, 35, 2805;
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the greatest er to date (86 : 14). Both 17d and 17e (entries 4
and 5) afforded 3 with detectable er’s but were ultimately less
efficient systems.
Conclusions
6 Selected examples: (a) E. P. Kündig, T. M. Seidel, Y. X. Jia
and G. Bernardinelli, Angew. Chem., Int. Ed., 2007, 46, 8484;
(b) C. T. Check, K. P. Jang, C. B. Schwamb, A. S. Wong,
M. H. Wang and K. A. Scheidt, Angew. Chem., Int. Ed., 2015,
54, 4264.
7 Selected examples: (a) F. Glorius, G. Altenhoff, R. Goddard
and C. Lehmann, Chem. Commun., 2002, 2704; (b) S. Würtz,
C. Lohre, R. Fröhlich, K. Bergander and F. Glorius, J. Am.
Chem. Soc., 2009, 131, 8344; (c) P. J. Czerwinski and
M. Michalak, Synthesis, 2019, 51, 1689.
In summary, a series of pseudo-enantiomeric carbohydrate-
based NHC-ligands featuring sterically differentiated groups at
positions C1 or C3 of the carbohydrate were synthesized by
simple glycosylation or SNAr strategies and evaluated in the
Rh-catalyzed hydrosilylation of acetophenone. We show that
ligands bearing a bulky group at C1 lead to a preference for
(S)-phenyl-1-ethanol, while the presence of large groups at C3
afforded preferentially the (R)-enantiomer. Our results suggest
this effect is achieved by the steric differentiation of the carbo-
hydrate’s C1 and C3 positions which flank the attachment to
the imidazolylidene scaffold. This “pseudoenantiomeric”
design feature is shown in Fig. 1.22
While our efforts to achieve a high level of asymmetric
induction in the benchmark hydrosilylation reaction11,12 have
been less successful, we have surpassed our previous result9
and shown, to the best of our knowledge for the first time, that
the judicial functionalization of carbohydrate synthons can
lead to pseudo-enantiomeric NHC-ligands for asymmetric
catalysis.
8 L. Benhamou, E. Chardon, G. Lavigne, S. Bellemin-
Laponnaz and V. César, Chem. Rev., 2011, 111, 2705.
9 Selected reviews: (a) M. Diéguez, O. Pàmies and
C. Claver, Chem. Rev., 2004, 104, 3189; (b) Carbohydrates:
Tools for Stereoselective Synthesis, ed. M. M. K. Boysen,
Wiley-VCH, Weinheim, 2013; (c) A. S. Henderson,
J. F. Bower and M. C. Galan, Org. Biomol. Chem., 2016,
14, 4008; (d) R. Pretorius, J. Olguin and M. Albrecht,
Inorg. Chem., 2017, 56, 12410; (e) M. E. Cucciolito,
A. D’Amora, G. De Feo, G. Ferraro, A. Giorgio, G. Petruk,
D. M. Monti, A. Merlino and F. Ruffo, Inorg. Chem., 2018,
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J. F. Wei and L. Jia, Eur. J. Inorg. Chem., 2007, 2221;
(g) J. P. Byrne, P. Musembi and M. Albrecht, Dalton
Trans., 2019, 48, 11838; (h) B. K. Keitz and R. H. Grubbs,
Organometallics, 2010, 29, 403; (i) W. H. Zhao, V. Ferro
and M. V. Baker, Coord. Chem. Rev., 2017, 339, 1;
( j) Z. G. Zhou, Y. Y. Yuan, G. H. Xu, Z. W. Chen and
M. Li, Prog. Chem., 2019, 31, 351; (k) T. Shibata,
H. Hashimoto, I. Kinoshita, S. Yano and T. Nishioka,
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10 (a) A. S. Henderson, J. F. Bower and M. C. Galan, Org.
Biomol. Chem., 2014, 12, 9180; (b) F. Tewes, A. Schlecker,
K. Harms and F. Glorius, J. Organomet. Chem., 2007, 692,
4593; (c) B. K. Keitz and R. H. Grubbs, Organometallics,
2009, 29, 403; (d) M. Guitet, P. Zhang, F. Marcelo, C. Tugny,
J. Jiménez-Barbero, O. Buriez, C. Amatore, V. Mouriès-
Mansuy, J.-P. Goddard, L. Fensterbank, Y. Zhang,
S. Roland, M. Ménand and M. Sollogoub, Angew. Chem.,
Int. Ed., 2013, 52, 7213.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
ASH thanks EPSRC Bristol Chemical Synthesis CDT EP/
G036764/1, JFB thanks Royal Society for a University Research
Fellowship and MCG thanks the ERC (COG: 648239) and
EPSRC CAF EP/L001926/1 and EPSRC EP/J002542/1 for funding.
Notes and references
1 (a) W. A. Herrmann and C. Köcher, Angew. Chem., Int. Ed.
Engl., 1997, 36, 2162; (b) N-Heterocyclic Carbenes, ed.
S. P. Nolan, Wiley-VCH, Weinheim, 2014.
Org. Biomol. Chem.
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