26
S.C. Pan, B. List
Scheme 20. Organocatalytic asymmetric transfer hydrogenation of different
α,β-unsaturated aldehydes
catalyst (Yang et al. 2005; for an independent study on the same reaction, see Ouelett et al. 2005). We found that upon treating aromatic,
trisubstituted α,β-unsaturated aldehydes 20 with a slight excess of dihydropyridine 21 and a catalytic amount of 19 at 13 °C in dioxane, the
corresponding saturated aldehydes 22 were obtained in high yields and
enantioselectivities (Scheme 20).
5
Asymmetric Counteranion Directed Catalysis
Most chemical reactions proceed via charged intermediates or transition
states. In asymmetric Brønsted acid catalysis the substrate is protonated
by the catalyst and a chiral H-bond-assisted ion pair is generated. We
reasoned that, in principle, any reaction that proceeds via cationic in-
S.C. Pan, B. List
Scheme 20. Organocatalytic asymmetric transfer hydrogenation of different
α,β-unsaturated aldehydes
catalyst (Yang et al. 2005; for an independent study on the same reaction, see Ouelett et al. 2005). We found that upon treating aromatic,
trisubstituted α,β-unsaturated aldehydes 20 with a slight excess of dihydropyridine 21 and a catalytic amount of 19 at 13 °C in dioxane, the
corresponding saturated aldehydes 22 were obtained in high yields and
enantioselectivities (Scheme 20).
5
Asymmetric Counteranion Directed Catalysis
Most chemical reactions proceed via charged intermediates or transition
states. In asymmetric Brønsted acid catalysis the substrate is protonated
by the catalyst and a chiral H-bond-assisted ion pair is generated. We
reasoned that, in principle, any reaction that proceeds via cationic in-