Bifunctional catalysis condensation reactions

Feedstock Reactions Catalyst References Acetone Condensation-hydrogenation (bifunctional catalysis) Pd on sulfonated PS-DVB [6] Methanol, Raffinate II Condensation, hydrogenation Pd on sulfonated PS-DVB [61] Dioxygen dissolved in water Hydrogenation Pd on sulfonated PS-DVB [8]... 

The availibility of three geometric isomers of our artificial enzyme lets us examine other reactions that can show bifunctional catalysis. Enolization of a ketone— and its addition to an aldehyde group in an aldol condensation—are two cases examined so far in which an isomer of our catalyst is preferred that is not the one that was best in the ribonuclease mimic. The geometric preference indicates something novel about the geometry of enolization reactions. 

Other publications have also appeared describing condensation kinetics with heterogeneous catalysts by a designed experimental approach to optimize reaction conditions, stannous octanoate condensation catalysis and the role of bifunctional catalysis mechanisms. A bifunctional transition state , shown for compound 8, was postulated to explain the kinetics of heterofunctional condensation reactions catalysed by CI3CCOOH, Et2NOH, MeEtC=NOH or CH3COOH (equation 6). 

Trost s group reported direct catalytic enantioselective aldol reaction of unmodified ketones using dinuclear Zn complex 21 [Eq. (13.10)]. This reaction is noteworthy because products from linear aliphatic aldehydes were also obtained in reasonable chemical yields and enantioselectivity, in addition to secondary and tertiary alkyl-substituted aldehydes. Primary alkyl-substituted aldehydes are normally problematic substrates for direct aldol reaction because self-aldol condensation of the aldehydes complicates the reaction. Bifunctional Zn catalysis 22 was proposed, in which one Zn atom acts as a Lewis acid to activate an aldehyde and the other Zn-alkoxide acts as a Bronsted base to generate a Zn-enolate. The... 

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