High pressure-assisted low-loading asymmetric organocatalytic conjugate addition of nitroalkanes to chalcones.

The application of high pressure (up to 9 kbar) allows for relatively fast (1-5 h) and highly enantioselective 1,4-addition of nitromethane and 2-nitropropane to chalcones at room temperature with substantial reduction of catalyst loading (0.2-1 mol% of cinchona alkaloid-based thioureas and squaramides). Various γ-nitroketones were obtained at 9 kbar with high yield and enantioselectivity (up to 98%), whereas in control experiments at atmospheric pressure usually only a small amount (<10%) of products were formed after 20 h.

Disulphide bond exchange inhibited by air - kinetic and thermodynamic products in a library of macrocyclic cysteine derivatives.

In this paper we present the synthesis and reactivity of dithiols comprising of two cysteine moieties attached to a dipicolinic acid core. Oxidation of these thiols provides oligomeric macrocycles. Monomers with 13-membered rings are kinetic products which are, however, strained and readily transform into higher oligomers under basic conditions or elevated temperature via a disulphide exchange reaction. Dimers, which are the most stable thermodynamic products, equilibrate only under inert conditions with thiolate as a catalyst. Under aerobic conditions, the thiols are oxidised before the equilibrium is reached.

8-Propyldithieno[3,2-b:2',3'-e]pyridine-3,5-diamine (DITIPIRAM) Derivatives as Neutral Receptors Tailored for Binding of Carboxylates.

The DITIPIRAM (8-propyldithieno[3,2-b:2',3'-e]pyridine-3,5-diamine)-based receptors 11 and 12 were readily synthesized, and their anion-binding properties were studied both in solution and in the solid-state. 1H NMR titrations revealed that receptor 12 equipped with two phenyl-urea groups preferentially binds carboxylates, even in the highly competitive DMSO-d6/CD3OH solvent mixture. X-ray analysis showed that receptor 12 exhibited great complementarity for benzoate, which is cooperatively bound by the means of four highly directional hydrogen bonds from the two urea groups. Comparison with the most effective acyclic receptors based on a structurally related rigid carbazole platform demonstrates that the DITIPIRAM motif provides a better suited geometry in the binding pocket, and consequently stronger anion binding.

Efficient and highly enantioselective construction of trifluoromethylated quaternary stereogenic centers via high-pressure mediated organocatalytic conjugate addition of nitromethane to ß,ß-disubstituted enones.

A very effective high-pressure-induced acceleration of asymmetric organocatalytic conjugate addition of nitromethane to sterically congested ß,ß-disubstituted ß-CF3 enones has been developed. A combination of pressure (8-10 kbar) and noncovalent catalysis with low-loading of chiral tertiary amine-thioureas (0.5-3 mol %) is shown to provide very efficient access to a wide range of γ-nitroketones containing trifluoromethylated all-carbon quaternary stereogenic centers in the ß-position (80-97%, 92-98% ee).