Hydrophobicity and mixing effects on select heterogeneous, water-accelerated synthetic reactions.

The influence of aqueous reaction media on organic reactions is a topic of long-standing interest, particularly as it affects the rate or selectivity of synthetic reactions. Sometimes such reactions appear homogeneous, typically in dilute solution, whereas others are obviously heterogeneous, typically in concentrated solution that is more characteristic of a preparative synthetic reaction. The latter situation has been termed "on water." Here, it is demonstrated that the rates of heterogeneous ene reactions, Passerini reactions, and Ugi reactions in pure water and in aqueous solutions are dependent on the mixing method and reactant polarity, consistent with the involvement of hydrophobic interactions in their acceleration.