Hydrophobic acceleration

Rideout, D. and R. Breslow (1980) Hydrophobic acceleration of Diels-Alder reactions. Journal of the American Chemical Society 102,7816-7817. 

Preliminary examples suggest that the techniques of hydrophobic acceleration and dry-state adsorption conditions recently applied to the acceleration of the all-carbon Diels-Alder reaction should prove equally useful in the Diels-Alder reactions of heterodienes. Hydrophobic acceleration T. A. Eggelte, H. De Koning and H. O. Huisman, Tetrahedron, 1973, 29, 2491 R. Breslow and D. C. Rideout, J. Am. Chem. Soc., 1980, 102, 7816 R. Breslow, U. Maitra and D. C. Rideout, Tetrahedron Lett., 1983, 24, 1901 dry-state adsorption conditions (Si02, florisil, alumina) V. V. Veselovsky, A. S. Gybin, A. V. Lozanova, A. M. Moiseenkov, W. A. Smit and R. Caple, Tetrahedron Lett., 1988, 29, 175 H. Parlar and R. Baumann, Angew. Chem., Int. Ed. Engl., 1981, 20, 1014 H. Parlar, R. Baumann and F. Korte, Z. Natursforsch., Teil B, 1981, 36, 898. 

Breslow R and Rideout DC. Hydrophobic Acceleration of Diels-Alder Reactions. 

Rideout, D. C. Breslow, R. Hydrophobic Acceleration of Diels-Alder Reactions. /. Am. Chem. Soc. 

Rideout DC, Breslow R (1980) Hydrophobic acceleration of diels-alder reactions. J Am Chem Soc... 

The reaction of two molecules of benzaldehyde to form benzoin is generally referred to as the benzoin condensation. It is normally catalyzed by cyanide ion, although thiazolium ions will also catalyze it, as we have discussed above and shown in Fig. 1.2. The normal solvent for the benzoin condensation is ethanol, to dissolve all the components of the reaction. However, it seemed to us likely that there would be overlap of the phenyl rings in the transition state for the benzoin condensation, and thus that reaction in water could lead to hydrophobic accelerations. This proved to be the case. We saw that the rate of the cyanide-catalyzed benzoin condensation was 200-fold faster in water than in ethanol. Also, we saw that added LiCl increased the reaction rate, while added lithium perchlorate decreased it. Such salt effects are diagnostic of the presence of some acceleration by hydrophobic packing in the transition state for the reaction. 

Biscoe, M., Uyeda, C. and Breslow, R., Requirements for selective hydrophobic accelerations in the reduction of ketones, Org. Lett., 2004,6,4331-4334. 

R. Breslow and Carmelo J. Rizzo, "Chaotropic Salt Effects in a Hydrophobically Accelerated Diels-Alder Reaction", T. Am. Chem. Soc. 113,4340-4341 (1991). 

E. T. Kool and R Breslow, "Dichotomous Salt Effects in the Hydrophobic Acceleration of the Benzoin Condensation", T. Am. 

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