Search results for "aldol"

ChemInform Abstract: A Catalytic Highly Enantioselective Direct Synthesis of 2-Bromo-2-nitroalkan-1-ols Through a Henry Reaction.

2009

Highly enantiomerically enriched 2-bromo-2-nitroalkan-1-ols are prepared by direct condensation of aliphatic and aromatic aldehydes with bromonitromethane in the presence of a catalytic amount of copper(II) acetate and a C1-symmetric camphor-derived amino pyridine ligand.

ChemInform Abstract: Enantioselective Addition of Nitromethane to 2-Acylpyridine N-Oxides. Expanding the Generation of Quaternary Stereocenters with …

2014

The direct asymmetric Henry reaction with prochiral ketones, leading to tertiary nitroaldols, is an elusive reaction so far limited to a reduced number of reactive substrates such as trifluoromethyl ketones or α-keto carbonyl compounds. Expanding the scope of this important reaction, the direct asymmetric addition of nitromethane to 2-acylpyridine N-oxides catalyzed by a BOX-Cu(II) complex to give the corresponding pyridine-derived tertiary nitroaldols having a quaternary stereogenic center with variable yields and good enantioselectivity, is described.

Stereoselective anti aldol reactions of erythrulose derivatives. Functionalized chiral d3 and d4 synthons.

2004

An improved procedure for the synthesis of anti aldols from protected erythrulose derivatives is reported. The preparation of functionalized d3 and d4 synthons with various stereochemical arrays by means of this methodology is described and subsequently applied to a stereoselective formal synthesis of the natural metabolite goniothalesdiol.

Bis(oxazoline) Lewis Acid Catalyzed Aldol Reactions of PyridineN-Oxide Aldehydes—Synthesis of Optically Active 2-(1-Hydroxyalkyl)pyridine Derivatives…

2006

A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro-chiral pyridine-N-oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1-oxypyridine-2-carbaldehyde derivatives catalyzed by chiral copper(II)-bis(oxazoline) complexes gave optically active 2-(hydroxyalkyl)- and 2-(anti-1,2-dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities-up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.

Theozyme for antibody aldolases. Characterization of the transition-state analogueElectronic supplementary information (ESI) available: MP2/6-31G** e…

2003

A theozyme for antibody aldolases has been studied at the MP2/6-31G** computational level. Formation of two cooperative hydrogen-bonds between the acidic hydrogen atoms of the enamine and of a methanol molecule with the oxygen atom of the aldol acceptor markedly favors the C–C bond-formation associated with the aldol reaction. A comparative analysis of the geometry, the charge distribution and the shape of the molecular electrostatic potential of the transition structure (TS) with the covalent adduct, resulting from the reaction of methylamine and the β-diketone used as a hapten allows us to characterize the transition-state analogue (TSA) generated at immunization. This finding allows us t…

New recyclable materials for L-proline-catalyzed aldol reactions

A Green Look at the Aldol Reaction

2005

Aldol reactions have been and are widely applied for the preparation of β-hydroxy aldehydes, β-hydroxy ketones or α,β-unsaturated aldehydes or ketones through addition or addition-elimination reactions of aldehydes and ketones. The study of the aldol reaction from the point of view of its greenness must have in mind first of all that a general synthetic method must be based on complete and efficient conversions of well defined selectivity and that greenness is more a term for comparison than an absolute kind of qualification. This comparison, when referred to the aldol reaction, applies here to the diverse modifications of the reaction. Thus, the original poorly selective, but highly atom e…

Organocatalytic Asymmetric Synthesis of Trifluoromethylated Tetrahydrocarbazoles by a Vinylogous Michael/Aldol Formal [4+2] Annulation

2018

Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions

2016

A novel one-pot, three-component diastereo- and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β-unsaturated pyrazolones, which react with a second equivalent of enal through an N-heterocyclic carbene (NHC)-catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3-diketones, 2,5-chromenediones are available through [2+4] annulation.

ChemInform Abstract: New Highly Asymmetric Henry Reaction Catalyzed by CuIIand a C1-Symmetric Aminopyridine Ligand, and Its Application to the Synthe…

2008

A new catalytic asymmetric Henry reaction has been developed that uses a C(1)-symmetric chiral aminopyridine ligand derived from camphor and picolylamine. A variety of aromatic, heteroaromatic, aliphatic, and unsaturated aldehydes react with nitromethane and other nitroalkanes in the presence of DIPEA (1.0 equiv), Cu(OAc)(2)*H(2)O (5 mol %), and an aminopyridine ligand (5 mol %) to give the expected products in high yields (up to 99 %), moderate-to-good diastereoselectivites (up to 82:18), and excellent enantioselectivities (up to 98 %). The reaction is air-tolerant and has been used in the synthesis of the antifungal agent miconazole.