2 B. Zhang and R. Breslow, J. Am. Chem. Soc., 1997, 119, 1676; M. W.
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4 (a) K. Kavallieratos, S. R. de Gala, D. J. Austin and R. H. Crabtree,
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Kobayashi and Y. Aoyama, Tetrahedron Lett., 1991, 4757.
6 (a) V. van Axel-Castelli, A. Dalla Cort, L. Mandolini and D. N.
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N–H sulfonamide resonance with trace protic impurity and the
chemical shift change for the C–H aromatic resonance being too
small to allow accurate titration monitoring. From literature
data,5a association constants in CH2Cl2 for hydrogen bond
receptors having two convergent hydrogen bond donor groups
with neutral carbonyl substrates are in the range of 1 to 2 3 103
M21. Assuming that the transition state is bound to the receptor
approximately as well as acetate (2 3 104 M21) an acceleration
factor of 10–20 is predicted, a value comparable with the
experimental value of 6.1.
Molecular cleft receptors, even very simple ones like 1, can
be catalytically active for reactions such as eqn. (1), where the
transition state for the slow step is thought to be bound more
strongly than starting materials or products. As a cleft rather
than a macrocycle, this receptor is expected to bind the substrate
carbonyl group without significantly blocking access of the
nucleophile to the carbonyl.
7 E. S. Gould, Mechanism and Structure in Organic Chemistry, Holt,
Reinhart and Winston, N.Y., 1959, p. 543.
We thank the US National Science Foundation for funding,
and Professor David J. Austin for valuable suggestions.
8 With excess amine, observing the disappearance of the p-Me and CHO
resonances of the aldehyde and the appearance of the p-Me and CH2
resonances of the imine. In a typical experiment, a 5 mm NMR tube
containing p-tolualdehyde (0.025 ml, 0.21 mmol) and anhydrous
MgSO4 (5.2 mg, 0.043 mmol) in 0.750 ml of CD2Cl2 was introduced
into the probe and left at 220 °C to equilibrate. Receptor 1 (6.3 mg,
0.016 mmol) was added and the spectrum recorded, then BnNH2 (0.250
ml, 2.3 mmol) was added and the aldehyde resonances (d 9.94, 2.45) and
the imine resonances (d 4.80, 2.41) were monitored. Plotting the
integration values vs. time for the first 20 min and linear fitting of the
straight line gave the initial rates.
Notes and references
1 (a) A. D. Hamilton, Frontiers in Bioorganic Chemistry, H. Dugas ed.,
Springer, Berlin, 1991, vol. 2. p. 117; (b) D. A. Bell and E. V. Anslyn,
Hydrogen-Bonding Receptors: Open-Chain Catalytic Systems, in
Comprehensive Supramolecular Chemistry, ed. F. Vögtle, Pergamon,
New York, 1996, vol. 2 ch. 14 pp. 439–475; (c) M. C. Feiters,
Supramolecular Catalysis, ed. D. N. Reinhoudt, Pergamon, New York,
1996, vol. 10, ch. 11, pp. 267–360; (d) R. Breslow, Acc. Chem. Res.,
1995, 28, 146; (e) A. J. Kirby, Angew. Chem., Int. Ed. Engl., 1996, 35,
707; (f) Y. Murakami, J. Kikuchi, Y. Hisaeda and O. Hayashida, Chem.
Rev. 1996, 96, 721.
9 F. A. Cotton and P. F. Stokely, J. Am. Chem. Soc., 1970, 92, 294; G.
Dauphin and A. Kergomard, Bull. Soc. Chim. Fr., 1961, 3, 486.
10 S. J. Benkovic, A. D. Napper and R. A. Lerner, Proc. Natl. Acad. Sci.
U.S.A., 1988, 85, 5355.
Communication 9/05838I
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Chem. Commun., 1999, 2109–2110