Please do not adjust margins
RSC Advances
DOI: 10.1039/C5RA12135C
COMMUNICATION
Journal Name
1
(a) Y. Hayashi, T. Sumiya, J. Takahashi, H. Gotoh, T.
Urushima, M. Shoji, Angew. Chem. Int. Ed. 2006, 45, 958-
the catalyst (See Figure 4 and ESI). Trifluoroacetate-catalyst
interactions were found to be crucial to define a catalytic cavity in
protonated aminobenzimidazole organocatalysts working in
9
61; (b) Y. Hayashi, S. Aratake, T. Okano, J. Takahashi, T.
Sumiya, M. Shoji, Angew. Chem. Int. Ed. 2006, 45, 5527-
529; (c) S. Aratake, T. Itoh, T. Okano, N. Nagae, T. Sumiya,
1
7
toluene. However, in the presence of water buffered at pH 7,
partial protonation of the amino group and easier dissociation of
the ion pairs makes unlikely that catalyst 1a·2TFA keeps such a tight
structure completely during the reaction, and the loss of one or
even both trifluoroacetate anions into solution is highly probable.
The persistence of the intramolecular hydrogen bond is in contrast
much more likely, and since it is closer to the dodecyl chain and
therefore the organic phase, it should be little affected by the
aqueous environment.
5
M. Shoji, Y. Hayashi, Y., Chem. Eur. J. 2007, 13, 10246-10256.
(a) N. Mase, Y. Nakai, N. Ohara, H. Yoda, K. Takabe, F.
Tanaka, C. F. Barbas, J. Am. Chem. Soc. 2006, 128, 734-735;
(b) N. Mase, K. Watanabe, H. Yoda, K. Takabe, F. Tanaka, C. F.
Barbas, J. Am. Chem. Soc. 2006, 128, 4966-4967.
(3) Selected references: (a) Z. Jiang, Z. Liang, X. Wu, Y. Lu,
Chem. Commun. 2006, 2801-2803; (b) G. Guillena, M. C. Hita,
C. Nájera, Tetrahedron: Asymmetry 2006, 17, 1493-1497; (c)
S. S. Chimni, D. Mahajan, Tetrahedron: Asymmetry 2006, 17,
2
3
2
108-2119; (d) S. Aratake, T. Itoh, T. Okano, T. Usui, M. Shoji,
Y. Hayashi, Chem. Commun. 2007 2524-2526; (e) S.
Guizzetti, M. Benaglia, L. Raimondi, G. Celentano, Org. Lett.
007, 9, 1247-1250; (f) C. Palomo, A. Landa, A. Mielgo, M.
Oiarbide, A. Puente, S. Vera, Angew. Chem. Int. Ed. 2007, 46,
431-8435; (g) Y. Hayashi, S. Samanta, H. Gotoh, H. Ishikawa,
,
2
8
Angew. Chem. Int. Ed. 2008, 47, 6634-6637; (h) Y. Hayashi, T.
Urushima, S. Aratake, T. Okano, K. Obi, Org. Lett. 2008, 10,
2
1-24; (i) C.-M. Lo, H.-F. Chow, J. Org. Chem. 2009, 74, 5181-
5191; (j) J. Xiao, F.-X. Xu, Y.-P. Lu, T.-P. Loh, Org. Lett. 2010
12, 1220-1223; (k) J. Li, Y. Liu, L. Liu, Lett. Org. Chem. 2012, 9,
1-55; (l) L. Qin, L. Zhang, Q. Jin, J. Zhang, B. Han, M. Liu,
Angew. Chem. Int. Ed. 2013, 52, 7761-7765; (m) A. Kumar, S.
S. Chimni, Tetrahedron 2013, 69, 5197-5204; (n) Y. Qiao, A.
D. Headley, Green Chem. 2013, 15, 2690-2694; (o) A. Psarra,
Figure 4. DFT (B3LYP/6-31G*) optimized structure for catalyst
,
1
a·2TFA showing hydrogen bonding (dotted lines). Hydrogen,
5
white; Carbon, grey; Fluorine, yellow; Oxygen, red; Nitrogen, blue.
Conclusions
C. G. Kokotos, P. Moutevelis-Minakakis, Tetrahedron 2014
0, 608-615; (p) J. Duschmale, S. Kohrt, H. Wennemers,
Chem. Commun. 2014, 50, 8109-8112. (q) F. Rodríguez-
Llansola, J. F. Miravet, B. Escuder, Chem. Commun. 2009
303-7305. (r) C. Berdugo, J. F. Miravet, B. Escuder, Chem.
Commun. 2013, 10608-10610.
(a) J. Mlynarski, J. Paradowska, Chem. Soc. Rev. 2008, 37,
502-1511; (b) J. Paradowska, M. Stodulski, J. Mlynarski,
,
7
In conclusion, we have shown that amphiphilic guanidinium
cations are efficient organocatalysts for asymmetric aldol reactions
in water, forming an unstable emulsion. Besides proving the high
dependence of reactivity and especially stereoselectivity on the
electronic nature of the aldehyde, which gives rise to a free energy
linear correlation, we have also found out that intramolecular
hydrogen bonding in 1a provides a particular locked conformation
that explains not only the structural rigidity of the catalyst as found
by NMR but the efficiency in conveying asymmetry during the
reaction as well. It is remarkable that this hydrogen bonding seems
to remain stable during the reaction in the presence of water. This
can be rationalized because the acyl-guanidinium hydrogen bond
stays close to the dodecyl chain and therefore must remain
embedded in the organic phase, rather than exposed to the
aqueous phase. Therefore the success of the system is sustained by
,
7
4
1
Angew. Chem. Int. Ed. 2009, 48, 4288-4297; (c) J. Mlynarski,
S. Bas, Chem. Soc. Rev. 2014, 43, 577-587.
(a) A. P. Brogan, T. J. Dickerson, K. D. Janda, Angew. Chem.
Int. Ed. 2006, 45, 8100-8102; (b) Y. Hayashi, Angew. Chem.
Int. Ed. 2006, 45, 8103-8104.
Recent examples: (a) C. Jimeno, J. Miras, J. Esquena,
ChemCatChem 2014, 6, 2626-2633. (b) C. Jimeno, J. Miras, J.
Esquena, Catal. Lett. 2013, 143, 616-623.
(a) E. Alza, X. C. Cambeiro, C. Jimeno, M. A. Pericàs, Org. Lett.
2007, 9, 3717-3720; (b) D. Font, C. Jimeno, M. A. Pericàs,
Org. Lett. 2006, 8, 4653-4655; (c) D. Font, S. Sayalero, A.
Bastero, C. Jimeno, M. A. Pericàs, Org. Lett. 2008, 10, 337-
5
6
7
a
delicate combination of intermolecular (hydrophobic) and
3
40.
intramolecular (H-bonds) non-covalent interactions. The
understanding of the structural factors (amphiphilicity and
conformational effects) governing the catalytic process will allow us
a further improvement of these catalysts for intended functions,
either in this or in related chemical processes.
8
9
(a) J. Atcher, I. Alfonso, RSC Adv. 2013, 3, 25605-25608; (b) J.
Atcher, A. Moure, I. Alfonso, Chem. Commun. 2013, 487-489;
(c) J. Solà, M. Lafuente, J. Atcher, I. Alfonso, Chem. Commun.
2014, 4564-4566; (d) J. Atcher, A. Moure, J. Bujons, I.
Alfonso, Chem. Eur. J. 2015, 21, 6869-6878.
Selected references: (a) C. Uyeda, E. N. Jacobsen, J. Am.
Chem. Soc. 2011, 133, 5062-5075; (b) C. Uyeda, E. N.
Jacobsen, J. Am. Chem. Soc. 2008, 130, 9228-9229; (c) C.
Uyeda, A. R. Roetheli, E. N. Jacobsen, Angew. Chem. Int. Ed.
Acknowledgements
2
010, 49, 9753-9756; (d) Y. Kobayashi, Y. Taniguchi, N.
Hayama, T. Inokuma, Y. Takemoto, Angew. Chem. Int. Ed.
013, 52, 11114-11118; (g) Y. Sohtome, B. Shin, N. Horitsugi,
Financial support from Ministerio de Economía y Competitividad
(
CTQ2012-38594-C02-02
and
CTQ2012-38543-C03-03)
and
2
Generalitat de Catalunya (2014 SGR 231) is gratefully
acknowledged. CJ is a Ramón y Cajal fellow (RYC-2010-06750).
K. Noguchi, K. Nagasawa, Chem. Asian J. 2011, 6, 2463-2470;
(h) Y. Sohtome, N. Takemura, K. Takada, R. Takagi, T. Iguchi,
K. Nagasawa, Chem. Asian J. 2007, 2, 1150-1160; (i) K.
Takada, K. Nagasawa, Adv. Synth. Catal. 2009, 351, 345-347;
(
1
l) L.-J. Wang, F.-F. Flu, Bull. Korean Chem. Soc. 2010, 31,
280-1282; (m) M. Orlandi, M. Benaglia, L. Raimondi, G.
Notes and references
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins