Trifunctional catalyst

Recently, Liu has developed a Bronsted acid activated trifunctional organocatalyst, based on the BINAP scaffold, that was used for the first time to catalyze aza MBH reactions between N tosylimines and MVK with fast reaction rates and good enantioselectivity at room temperature. This trifunctional catalyst containing a Lewis base, a Bronsted base and a Bronsted acid, required add activation to confer its enantioselectivity and rate improvement for both electron rich and electron deficient imine substrates. The role of the amino Lewis base of 27 was investigated and found to be the activity switch in response to an acid additive. The counterion of the acid additive was found to influence not only the excess ratio but also the sense of asymmetric induction (Scheme 13.23) [36]. 

Scheme 3.32 Aza-Morita-Baylis-Hillman reactions catalysed by trifunctional catalyst.

Synthetic highlights The partial synthesis of paclitaxel was necessary to enhance the availability of the drug substance and avoid unsustainable use of yew trees. Many different synthetic routes have been reported and three inventive pathways for the enantioselective or site-selective approaches to various segments of the paclitaxel molecule are described. These are aU promoted by organometal catalytic complexes. Reactions presented include use of the intramolecular Heck reaction in the synthetic pathway to baccatine III the Sharpless reaction and the introduction of a trifunctional catalyst for biomimetic synthesis of chiral diols synthesis of the paclitaxel side-chain and use of a Zr-complex catalyst in the reductive N-deacylation of taxanes to primary amine, the key precursor of paclitaxel. 

Trifunctional Catalyst for Biomimetic Synthesis of Chiral Dials Synthesis of the Paclitaxel Side-Chain... 

As indicated in the introductory paragraph of this section, the most efficient dihydroxylation was achieved with heterogeneous catalysts. Scheme 14.11 presents the catalytic cycle in the AD reaction catalyzed by the heterogeneous trifunctional catalyst [42]. 

Using the trifunctional catalyst in the one-pot reaction for the preparation of diol 2R,3S-27, the authors completed synthesis of the side chain of paclitaxel according to Scheme 14.12. 

Table 14 2 Synthesis of chiral diols using the heterogeneous trifunctional catalyst (LDH-...

The single-pot biomimetic synthesis of chiral diol 27, mediated by the recyclable trifunctional catalyst, Na2PdCl4-K20s04-Na2W04 embedded in a matrix of layered double hydroxides, resulted in an efficient, low cost process. This protocol provided the desired prochiral olefin from Heck precursors and the in situ recycling of NMM to NMO. The whole process starts with cheap precursors and minimizes the number of unit operations. Other similar broad, interdisciplinary studies which led to an extraordinarily selective solution to the splitting of the amide bond in a mixture of compounds from a natural source will be considered in the next section. 

Scheme 7.13 Methanolysis of vinyl trifluoroacetate catalyzed by Sakai s trifunctional catalyst 56...

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