Diastereoselective chelation-controlled additions to β-silyloxy aldehydes

A general diastereoselective method for the addition of dialkylzincs and (E)-di- and (E)-trisubstituted vinylzinc reagents to β-silyloxy aldehydes is presented. This method employs alkyl zinc triflate and nonaflate Lewis acids and affords chelation-controlled products (6:1 to > 20:1 dr).     

Enantioselective synthesis of gabapentin analogues via organocatalytic asymmetric Michael addition of α-branched aldehydes to β-nitroacrylates

Michael addition reaction of α-branched aldehydes to β-nitroacrylates was successfully carried out by using a mixed catalyst consisting of a primary amino acid, L-phenylalanine, and its lithium salt to give β-formyl-β'-nitroesters having a quaternary carbon centre in good yields (up to 85%) with high enantioselectivity (up to 98% ee). By using benzyl β-nitroacrylates as Michael acceptors, the obtained β-formyl-β'-nitroesters were converted into various 4,4-disubstituted pyrrolidine-3-carboxylic acids including analogues of gabapentin (Neurotin(?)) in one step from the Michael adducts in high yields.     

Asymmetric organocatalytic oxy-Michael addition of alcohols to α,β-unsaturated aldehydes

A 1,4-addition of alcohols to α,β-unsaturated aldehydes was found to be efficiently promoted by biphenyldiamine-based catalyst 3 without formation of the acetals. An asymmetric variant of this reaction has also been performed by designing a novel axially chiral organocatalyst (R)-10c.     

Enantioselective organocatalytic formal allylation of α-branched aldehydes

Heteroarylvinyl sulfone 1 has been successfully used as a new sulfonyl Michael acceptor in aminocatalytic reactions with branched aldehydes. Subsequent one-pot Julia-Kocienski olefination allows the challenging preparation of enantiomerically pure α-allylated aldehydes bearing C-α quaternary carbons.     

Enantioselective organocatalytic α-sulfamidation of aldehydes using sulfonyl azides

Enantioselective organocatalytic α-sulfamidation of unbranched aldehydes is described using MacMillan’s second-generation imidazolidinone catalyst and o-nitrobenzenesulfonyl azide. The reactions are highly stereoselective (89.9–96.3% ee) with yields up to 71%. A strong correlation between aldehyde structure and product yield was found to exist, with 3-arylpropanals providing the best results. Application to functionalized amino acid synthesis is presented.     

Stereoselective synthesis of the dolastatin units by organotrifluoroborates additions to α-amino aldehydes

Dolastatin units were synthesized from the 1,2-addition reactions of potassium allyl or crotyltrifluoroborate salts to aldehyde derivatives from natural amino acids. The reactions were carried out in presence of a phase-transfer catalyst in a biphasic medium at room temperature and excellent yields (>89-93%) and stereoselective (>90:10 to 98:2) were obtained. The dolastatin units 8 and 14a-b were obtained after three steps in good overall yields (50-62%).     

Highly asymmetric Michael additions of α,α-disubstituted aldehydes to β-nitroalkenes promoted by chiral pyrrolidine-thiourea bifunctional catalysts

A series of secondary amine-thiourea catalysts derived from l-proline and chiral diamine were prepared and first applied to the Michael addition of α,α-disubstituted aldehydes to trans-β-nitroalkenes. Moderate yields (47-75%) and excellent enantioselectivities (up to 96% ee) were obtained for a variety of aryl and heteroaryl nitroalkenes.     

Highly enantioselective organocatalytic α-selenylation of aldehydes using hypervalent iodine compounds

The highly enantioselective organocatalytic α-selenylation reaction of aldehydes using a hypervalent iodine compound as an oxidative agent from commercially available phenyl diselenide under mild oxidative conditions is described. This transformation affords α-selenyl aldehydes in good yields and with excellent enantioselectivities. By using hypervalent iodine compounds, it opens up a suitable and alternative way for the preparation of biologically active building blocks such as β-hydroxy alcohols, α-amino acids, and α-hydroxy esters.     

Highly efficient asymmetric organocatalytic Michael addition of α,α-disubstituted aldehydes to nitroolefins under solvent-free conditions

A chiral pyrrolide-based diamine in combination with benzoic acid has been found to be an effective organocatalyst for Michael addition of α,α-disubstituted aldehydes with nitroolefins. The reaction provided the desired Michael products possessing all-carbon quaternary center with high yields (76–98%) and high levels of enantioselectivities (up to 97% ee) under solvent-free reaction conditions. The procedure presented is simple and makes this method suitable for practical use.     

Oxygen–chlorine interactions in the transition state of asymmetric Michael additions of carbonyl compounds to β-nitrostyrene

An oxygen–chlorine interaction is reported in the transition state of the Michael addition of acetone to nitrostyrene catalyzed by enantioenriched monosulfonamides. The interaction between the oxygen from the nitro group and the chlorine at the ortho-position of the sulfonamide moiety is supported by theoretical calculations. Asymmetric Michael addition products catalyzed by monosulfonamides were obtained in moderate yields and enantioselectivities.     

A Complete Solution to a Conjecture on the β-Polynomials of Graphs

In 1990, Gutman and Mizoguchi conjectured that all roots of the -polynomial (G,C,x) of a graph G are real. Since then, there has been some literature intending to solve this conjecture. However, in all existing literature, only classes of graphs were found to show that the conjecture is true; for example, monocyclic graphs, bicyclic graphs, graphs such that no two circuits share a common edge, graphs without 3-matchings, etc, supporting the conjecture in some sense. Yet, no complete solution has been given. In this paper, we show that the conjecture is true for all graphs, and therefore completely solve this conjecture.     

Enantioselective conjugate addition of oximes to trisubstituted β-nitroacrylates: an organocatalytic approach to β(2,2)-amino acid derivatives

A highly enantioselective organocatalytic intermolecular conjugate addition of oximes to β-nitroacrylates has been developed. The highly functionalized adducts obtained are valuable precursors for asymmetric synthesis, as demonstrated by the synthesis of β(2,2)-amino acids and oxazolidin-2-ones.     

Condensation of polyfluorinated β-diimines with aromatic aldehydes

Polyfluorinated 2-arylpyrimidines were synthesized by the reaction of polyfluorinated -diimines with aromatic aldehydes.     

Complete configuration interaction and π-shell structure in 10-center conjugated systems

An exact -electron calculation is presented for the ground singlet and lowest triplet states in naphthalene, azulene, and linear and cyclic decapentaene.Kharkov University. Translated from Teoreticheskaya i Éksperimental'naya, Vola 27, No. 4, pp. 452–455, July–August 1991. Original article submitted January 14, 1991.     

Role of quaternary ammonium salts as new additives in the enantioselective organocatalytic β-benzylation of enals

We report herein the efficiency of quaternary ammonium salts as co-catalysts in organocatalytic Michael reactions involving iminium activation of α,β-unsaturated aldehydes. The enantioselective formal benzylation of these substrates has been optimized and used to rationalize the role of the ammonium salts in these processes.     

β-Cyclodextrin promoted oxidation of aldehydes to carboxylic acids in water

A facile,efficient and substrate-selective oxidation of aldehydes to carboxylic acids with NaClO catalyzed byβ-cyclodextrin in water has been developed.A series of aldehydes which could form inclusion complex withβ-cyclodextrin(β-CD)were oxidized selectively with excellent yields.