Effect of water on chemo- and endo-selectivity in high pressure Diels-Alder furan reactions. Hydrophobic or polar effects?

Effect of aqueous PEG or PPG solvents on reaction selectivity and Gibbs energies

“…It has been proposed in the literature that Diels-Alder reaction endo:exo ratios can be influenced by a number of solvent properties: solvophobic interactions, hydrogen bonding, and polarity interactions (Ahmad-Zadeh Samii et al, 1985;Cativiela et al, 1994Cativiela et al, , 1996Jenner, 1994;Otto and Engberts, 2000). From our kinetic data alone, it is difficult to determine if the differences in the product ratio are caused from solvophobic interactions, hydrogen bonding, and/or polarity interaction as Rate constants in ethanol and 1-propanol from Blokzijl et al (1991).…”

Catalytic activity of cycloaurated complexes in the addition of 2‐methylfuran to methyl vinyl ketone

“…As a suitable reaction we chose the gold(III)-catalysed addition of 2-methylfuran (1) to methyl vinyl ketone (MVK) (2) to give 4-(5-methyl-2-furanyl)butan-2-one (3) (Scheme 1). The reaction occurs under a number of different conditions, including carrying out the reaction in the presence of an ethereal solution of BF 3 at low temperatures [13] or by using high pressures; [14] Cu(O 3 SCF 3 ) 2 has also been shown to catalyse the reaction. [15] A mechanism for the catalytic cycle has been proposed on the basis of NMR experiments, using AuCl 3 as the catalyst; [16] the first step in the reaction was proposed to be the auration of the furan at the 2-position.…”

Kinetic effect of pressure on Michael and Diels-Alder reactions in aqueous solutions

“…Comparison of the respective values shows that whereas E was little affected, operation in water produced a change of ln A and DS ≠ . (b) In a previous paper, 29 it was shown that for furan cycloaddition (entry 3) the stereoselectivity was dependent on the polarity of the medium: the endo selectivity decreased with increasing polarity except in water, which favoured the most compact endo transition state. The result was rationalized by considering simultaneously hydrophobic interactions and polarity effects.…”

“…In an earlier paper, we suggested that hydrogen bonding is likely to intervene in aqueous Diels-Alder reactions involving MVK. 29 Taking into account hydrophobic and electrostatic effects, we suggest the following expression for DV…”

“…27 To our knowledge, the pressure effect in aqueous DielsAlder reactions has not yet been reported except in a recent paper describing the condensation of anthracene-9-methanol and N-ethylmaleimide 28 and in a study emanating from our laboratory. 29 The pressure kinetics of several Diels-Alder reactions were studied in CH 2 Cl 2 and H 2 O. The cycloadditions considered were normal electron demand cycloadditions (entries 1-4 and 6) and one inverse electron demand reaction (entry 5).…”