[reaction: see text] A new class of thiourea catalysts have been developed which integrate saccharide and primary amine moieties into one small organic molecule. These simple catalysts are shown to be highly enantioselective for direct Michael addition of aromatic ketones to a range of nitroolefins (up to 98% ee).

A new catalytic stereoselective tandem transformation via Nazarov cyclization/electrophilic fluorination has been accomplished. This sequence is efficiently catalyzed by a Cu(II) complex to afford fluorine-containing 1-indanone derivatives with two new stereocenters with high diastereoselectivity (trans/cis up to 49/1). Three examples of catalytic enantioselective tandem transformation are presented.

An efficient, catalytic, diastereo- and enantioselective conjugate addition of N-(diphenylmethylene)glycine tert-butyl ester to β-aryl substituted enones was realized in the presence of 1 mol% of newly desired dinuclear N-spiro-ammonium salts, affording functionalized α-amino acid derivatives in 57-98% yields with high diastereoselectivity (up to 99:1 dr) and enantioselectivity (up to 96.5:3.5 er).

A one-pot three-component cascade reaction proceeds by way of a Lewis acid-catalyzed Knoevenagel condensation/Nazarov cyclization/electrophilic fluorination sequence to afford fluorinated 1-indanone derivatives in moderate to good yields with high diastereoselectivities.

Catalytic asymmetric synthesis provides one of the most powerful and economical approaches for the preparation of a variety of enantiomerically enriched compounds that are critical to developments in medicine, biology, and materials science. [1] In this scenario, the development of environmentally friendly, highly efficient, and selective chiral catalysts is important. Therefore, one crucial objective is the design and synthesis of new chiral catalysts, which enable challenging and/or previously unknown asymmetric transformations to occur in a highly efficient way. The requirement of maximum conformational rigidity is central to the design of a chiral catalyst. The rigid structure of the catalyst would enhance the enantiofacial differentiation by minimizing the possibilities of different conformers available to the coupling partners, and thus, deliver the maximum asymmetric induction from the chiral catalyst.[2] These semiempirical criteria have been applied to the creation of thousands of chiral catalysts in accord with the increasing need for enantiopure medicinal agents and the rapid advancement of the field of asymmetric synthesis.[3] Furthermore, most efficient catalysts with rigid structures, such as cinchona alkaloids, salen complexes, and binol (1,1'-bi-2-naphthol) derivatives, have demonstrated useful levels of enantioselectivity for a wide range of different asymmetric reactions.[4] On the other hand, the conformational flexibility is another fundamental characteristic of a chiral catalyst. Keeping the conformational flexibility at an optimal level is also essential to the catalyst reactivity and stereoselectivity. However, the effect of an appropriate balance between the conformational rigidity and flexibility in asymmetric catalysis has largely been ignored.[5] Herein we report the development of new chiral quaternary ammonium salts as phase-transfer catalysts (PTC) based on the concept of a linker-dictated structure that tunes rigidity and flexibility. This strategy led to the discovery of two catalysts that give access to both enantiomeric products of a catalyzed addition reaction from a common chirality source.In recent years, chiral phase-transfer catalysis has emerged as an area of intense interest in asymmetric synthesis owing to its operational simplicity and mild reaction conditions.[6] Although impressive new advances have been made, there appears a growing number of challenging substrates and difficult transformations that cannot be promoted by existing phase-transfer catalysts. One such instance involves the conjugate addition of nitroalkanes to enones to give products that are useful and versatile precursors for a variety of structures such as aminocarbonyl compounds, aminoalkanes, and pyrrolidines. [7] Although the reactions can be successfully carried out with simple, unhindered linear nitroalkanes in high enantioselectivity, [8] utilization of sterically more demanding nitroalkanes for the reaction of bulky b-aryl-substituted enones such as the chalcones can be less rewarding.[9] Varia...

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Enantioselective syntheses O 0031Highly Enantioselective Michael Addition of Aromatic Ketones to Nitroolefins Promoted by Chiral Bifunctional Primary Amine-Thiourea Catalysts Based on Saccharides. -Thiourea bearing a chiral diamine and a saccharide unit represents a new type of organocatalyst for the asymmetric Michael addition of aryl ketones (I) to nitroolefins (II). A wide variety of substituents is tolerated on both substrates, and only low influence of electronic properties on reaction outcome is observed. -(LIU, K.; CUI, H.-F.; NIE, J.; DONG, K.-Y.; LI, X.-J.; MA*, J.-A.; Org. Lett. 9 (2007) 5, 923-925; Dep. Chem., Tianjin Univ., Tianjin 300072, Peop. Rep. China; Eng.) -Mischke 30-027

A phase‐transfer‐catalyzed asymmetric Michael addition of (iminomethyl)phosphonates to α,β‐unsaturated ketones is described. In the presence of 1 mol‐% of a chiral dinuclear N‐spiro ammonium salt, the addition reaction proceeded smoothly to afford the adducts in up to 97 % yield with up to 99:1 dr and 78 % ee. One of the products was readily converted into a cyclic α‐aminophosphonic acid derivative without any erosion of the enantiopurity.