Diels-Alder reactions in aqueous solutions. Enforced hydrophobic interactions between diene and dienophile

Origins of Stereoselectivity in Diels−Alder Cycloadditions Catalyzed by Chiral Imidazolidinones

“…[23][24][25] In water the endo selectivity enhancement is accompanied by a considerable reaction acceleration due to enforced hydrophobic interactions between diene and dienophile. [28][29][30][31] The introduction of an alkyl group at R 2 slightly decreases the endo selectivity, 26 while an inversion of the endo orientation is observed when the hydrogen atom at R 3 is substituted by an alkyl group. 26,27 The results were attributed to an attractive C-H···π interaction between the methyl group and the diene π-system.…”

Three-component process for the synthesis of 4-amino-5- pyrimidinecarbonitriles under thermal aqueous conditions or microwave irradiation

“…The enhanced reactivity and selectivity observed in some reactions have been rationalized by various authors as being a consequence of hydrophobic effects and enforced hydrophobic interactions. [28][29][30][31] When the reaction was carried out in alcoholic solution good yields were obtained due to the solubility of all the reagents in alcohol solvent. Microwave-assisted solvent-free synthesis in organic reactions has been of growing interest as an efficient, economic and clean procedure ("green chemistry").…”

Understanding organic reactions in water: from hydrophobic encounters to surfactant aggregates

“…Later we found that the secondorder rate constant for the DA reaction of 5-methoxynaphthoquinone with CP was about 1.3 3 10 4 times higher in water than in n-hexane. 43 Detailed examination of aqueous solvent effects on the otherwise solvent-insensitive DA reactions showed that enforced hydrophobic interactions between diene and dienophile and hydrogen bonding of water to the polarised carbonyl moieties in the activated complex play a major role in the large aqueous rate acceleration. 45 The enhanced preference for the endo reaction product (mentioned above) is understood in terms of the smaller solvent accessible surface area for the activated complex leading to this stereoisomer.…”