Highly enantioselective Michael addition of acetone to nitroolefins catalyzed by chiral bifunctional primary amine-thiourea catalysts with acetic acid

Synthesis and Applications of Carbohydrate-Based Organocatalysts

Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described.

Asymmetric organocatalytic synthesis of tertiary azomethyl alcohols: key intermediates towards azoxy compounds and α-hydroxy-β-amino esters

A series of peracylated glycosamine-derived thioureas have been synthesized and their behavior as bifunctional organocatalysts has been tested in the enantioselective nucleophilic addition of formaldehyde tert-butyl hydrazone to aliphatic α-keto esters for the synthesis of tertiary azomethyl alcohols. Using the 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-β-d-glucosamine derived 3,5-bis-(trifluoromethyl)phenyl thiourea the reaction could be accomplished with high yields (75-98%) and moderate enantioselectivities (50-64% ee). Subsequent high-yielding and racemization-free tranformations of both aromatic- and aliphatic-substituted diazene products in a one pot fashion provide a direct entry to valuable azoxy compounds and α-hydroxy-β-amino esters.

Progress in aminosugar derived asymmetric organocatalysis

This review sheds light on the effect of the structural modification of sugar amines on their catalytic efficiency and the stereoselectivity of the reaction.

Liposome Membrane as a Platform for the L-Pro-Catalyzed Michael Addition of trans-β-Nitrostyrene and Acetone

Herein, we show that the L-proline (L-Pro)-catalyzed Michael addition of trans-β-nitrostyrene and acetone can proceed in "water" using liposome membranes and that the membrane fluidity and polarity are major controlling factors for this reaction. The highest conversion and rate constant of the reaction within the liposomes was achieved with the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dipalmitoyl-3-trimethylammoniumpropane (DPTAP) system. The catalytic activity of L-Pro in the liposome suspension was found to be comparable to that in a DMSO system. The reaction rate constant was found to be controlled by both the phase state of the liposome membrane and the surface charge on the membrane. Greater enantioselectivity was achieved in the presence of the liposomes than in DMSO solution, with corresponding enantiomeric excess values of 97.6% for the DOPC/DPTAP liposome system and 10% in DMSO. The hydrophobic region of the liposome membrane, which is a relatively stable self-organizing system, can serve as an effective "platform" for molecular recognition and selective conversion in aqueous media.

New ureas containing glycosyl and diphenylphosphinyl scaffolds: synthesis and the first attempts to use them in asymmetric synthesis

Chiral ureas containing glycosyl and diphenylphosphinyl scaffolds were found to be an effective organocatalyst. They were synthesised in high yields by a one-pot tandem Staudinger/aza-Wittig coupling reaction. The first attempts of using them in asymmetric synthesis are presented. Yields of the Morita-Baylis-Hillman reaction were moderate with an enantiomeric excess of up to 80%.

Bifunctional primary amine-thioureas in asymmetric organocatalysis

Research disclosed since the demonstration of the first examples of primary amine-thiourea organocatalysis in 2006 has shown that primary amine-based thioureas can successfully catalyze a diverse variety of highly enantioselective transformations providing a wide range of versatile organic compounds. Recent remarkable progress with these chiral catalysts is summarized in this review.

Asymmetric Michael addition of ketones to nitroolefins: pyrrolidinyl-oxazole-carboxamides as new efficient organocatalysts

New pyrrolidinyl-oxazole-carboxamides were synthesized and utilized as efficient organocatalysts for asymmetric Michael addition reaction. In addition, computational mechanistic studies were performed.

Catalyst-free and solvent-free Michael addition of 1,3-dicarbonyl compounds to nitroalkenes by a grinding method

An environmentally benign, fast and convenient protocol has been developed for the Michael addition of 1,3-dicarbonyl compounds to β-nitroalkenes in good to excellent yields by a grinding method under catalyst- and solvent-free conditions.