Search results for "Bifunctional"
showing 3 items of 123 documents
Bifunctional Acid-Base Catalysis
2011
Acid-base catalysis with bifunctional catalysts is a very prominent catalytic strategy in both small-molecule organocatalysts as well as enzyme catalysis. In both worlds, small-molecule catalysts and enzymatic catalysis, a variety of different general acids or hydrogen bond donors are used. In this chapter, important parallels between small molecule catalysts and enzymes are discussed, and a comparison is also made to the emerging field of frustrated Lewis pair catalysis.
Organocatalysts Fold to Generate an Active Site Pocket for the Mannich Reaction
2017
Catalysts containing urea, thiourea and tertiary amine groups fold into a three-dimensional organized structure in solution both in the absence as well as in the presence of substrates or substrate analogues, as indicated by solution NMR and computational studies. These foldamer catalysts promote Mannich reactions with both aliphatic and aromatic imines and malonate esters. Hammett plot and secondary kinetic isotope effects provide evidence for the C-C bond forming event as the turnoverlimiting step of the Mannich reaction. Computational studies suggest two viable pathways for the C-C bond formation step, differing in the activation modes of the malonate and imine substrates. The results sh…
Organocatalytic Enantioselective Vinylogous Henry Reaction of 3,5-Dimethyl-4-nitroisoxazole with Trifluoromethyl Ketones
2017
The enantioselective vinylogous Henry reaction of 3,5-dimethyl-4-nitroisoxazole with trifluoromethyl ketones employing a bifunctional squaramide organocatalyst has been developed. A series of isoxazole bearing trifluoromethyl-substituted tertiary alcohols, 2-substituted (R)-1,1,1-trifluoro-3-(3-methyl-4-nitroisoxazol-5-yl)propan-2-ols, were obtained under these mild reaction conditions in good yields and moderate to good enantioselectivities