Amphiphilic proline and prolylproline derivatives in the rhodium(I)-catalyzed asymmetric hydrogenation in water: Chiral induction as indication of the location of reactants within the micelle

Abstract

Proline and prolylproline dipeptide derived surfactants promote the asymmetric hydrogenation of (Z)‐methyl α‐acetamidocinnamate in water in the presence of the catalytic system [Rh(cod)2]BF4 + BPPM. Activity and enantioselectivity are enhanced significantly and the results in water are similar to those obtained with organic solvents. The possibility of a chiral induction was investigated in the presence of the optically active amino acid and peptide amphiphiles and an achiral rhodium catalyst [Rh(bdpb)(cod)]BF4. The analysis of the low optical induction gave some indications of the site where the reaction takes place within the micelle. Selected critical micelle concentrations (cmc) of the new prepared surfactants were determined by surface tension measurements. Chirality 10:754–759, 1998. © 1998 Wiley‐Liss, Inc.

Reactions in Micellar Systems

“…[155] In the previous examples the enantioselectivity was induced by the catalyst. Only low inductions of up to 11 % have been observed when nonchiral catalysts and optically active surfactants, such as derivatives of cholesterol, [156] carbohydrates, [157] and a-amino acids, [158] have been employed. The use of (d)-and (l)-prolinates as well as (d,d)-, (l,l)-, (d,l)-, and (l,d)-prolylprolinates as hydrophilic head groups have given particularly important clues about the reaction site within the micelle.…”

“…The use of (d)-and (l)-prolinates as well as (d,d)-, (l,l)-, (d,l)-, and (l,d)-prolylprolinates as hydrophilic head groups have given particularly important clues about the reaction site within the micelle. [158] The transfer of chirality implies that the hydrogenation takes place in the palisade layer, that is, at the interface of the head group with the hydrophobic core. [2a] Other important hints at a intramicellar mechanism were gained from "pulsed field gradient spin echo" NMR (PGSE-NMR) measurements.…”

Polymerized Ionic Amphiphiles: Synthesis and Effects in the Enantioselective Hydrogenation of an Amino Acid Precursor

“…Figures 1 b, 2 a, b) in comparison to sample poly 3 (see Figure 1 a) may be caused by an impeded diffusion of the reactants or a reduced solubility of the clustered aggregates although the asymmetric hydrogenation seems to proceed in the palisade layer near the micelle surface (transition region between hydrophilic headgroups and hydrophobic tails). [44] Apart from that it seems reasonable to assume that solubilization of reactants and therefore catalytic activity should be higher in case of small aggregates possessing a far larger surface than the clustered aggregates. Table 1. Quite another situation is met with the amphiphile 7 (Table 5) possessing a sulfate headgroup.…”

Self-assembly properties of some chiral N-palmitoyl amino acid surfactants in aqueous solution

“…As could be expected, the racemic mixtures did not generate a CD spectrum. For all pure enantiomers, the spectrum showed a CD band peaking between 210 and 220 nm that can be attributed to the π-π * transition of the amide carbonyl group [53,54]. The molar ellipticity was quite low.…”