Direct Aldol Addition Research Articles

Synthesis of the seed germination stimulant 3-methyl-2 H-furo[2,3- c]pyran-2-ones utilizing direct and regioselective Ti-crossed aldol addition

3-Methyl-2 H-furo[2,3- c]pyran-2-ones 1 and 2, a unique and remarkable seed germination stimulant, and its analogue were synthesized using direct and regioselective Ti-crossed aldol addition between dihydro-2 H-pyran-3(4 H)-ones and methyl pyruvate as the key step, followed by furanone formation.

ChemInform Abstract: Noncovalently Supported Heterogeneous Chiral Amine Catalysts for Asymmetric Direct Aldol and Michael Addition Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: A Facile and Efficient anti‐Selective Four‐Component Direct Aldol Addition via Chemoselective Thioester Enolate Formation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Noncovalently Supported Heterogeneous Chiral Amine Catalysts for Asymmetric Direct Aldol and Michael Addition Reactions

A new strategy for the immobilization of asymmetric organocatalysts by combining polystyrene (PS)/sulfonic acids and chiral amines in situ through acid-base interactions is presented. The PS/sulfonic acids play a dual role as catalyst anchors and modulators for activity and stereoselectivity. Different types of polymeric sulfonic acids were examined and 1% divinylbenzene (DVB) cross-linked PS/sulfonic acid 1 e with a medium loading of sulfonic acid moieties was found to be the optimal support. Furthermore, the noncovalency of this system allows combinatorial screening of optimal catalysts for the targeted reactions. In this regard, highly efficient and enantioselective heterogeneous catalysts were identified for the asymmetric direct aldol and Michael addition reactions. The catalysts could be easily recovered by filtration and reused for six cycles with similar stereoselectivity but slightly decreased activity. Significantly, the deactivated catalysts could be regenerated following an acidic washing/amine recharging procedure.

Tetranuclear BINOL−Titanium Complex in Selective Direct Aldol Additions

The extremely robust and water-stable tetranuclear complex Ti(4)(micro-BINOLato)(6)(micro(3)-OH)(4) (1) catalyzes the direct aldol addition with high degrees of regioselectivity at the sterically more encumbered alpha-side of unsymmetrical ketones. The formation of quaternary stereocenters is described. Oxygen-containing ene components can also be used as starting material in these reactions. When used with aliphatic aldehydes, acetals 18 or acetals of aldol adducts 20 were observed. As few as 0.2 mol % loadings with this catalyst 1 were enough to complete the reactions. Mechanistical aspects of the reactions are discussed.

A Facile and Efficient Anti-Selective Four-Component Direct Aldol Addition via Chemoselective Thioester Enolate Formation

A facile and efficient four-component anti-selective direct aldol addition of thioester enolates has been developed that is fully compatible with enolizable aldehydes and able to be conducted using untreated reagent-grade CH2Cl2 open to the air. The thioester enolates are generated in situ via an acylation/conjugate addition sequence using commercially available PhSLi and acryloyl chloride, thus avoiding prior enolate formation while maintaining complete chemoselectivity. The organosulfur products are convertible into various polyketide-based structures.

Amine‐Catalyzed Direct Aldol Addition.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Novel Synthons from Mucochloric Acid: The First Use of α,β‐Dichloro‐γ‐butenolides and γ‐Butyrolactams for Direct Vinylogous Aldol Addition.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Amine-Catalyzed Direct Aldol Addition

An efficient organo-catalytic, highly syn-stereoselective method for aldol additions between enolizable aldehydes and hydroxyacetone as well as dihydroxyacetone is disclosed. Reactions proceed in the presence of tertiary amines at room temperature. The aldol adducts can be obtained in good to high yields and with high degrees of syn-diastereoselectivity. This new aldol reaction provides an operationally simple protocol for the stereocontrolled synthesis of carbohydrates

Novel Synthons from Mucochloric Acid: The First Use of α,β-Dichloro-γ-butenolides and γ-Butyrolactams for Direct Vinylogous Aldol Addition

Novel 5-(1'-hydroxy)-gamma-butyrolactone and gamma-butyrolactam subunits were synthesized by direct vinylogous aldol addition of alpha,beta-dichloro gamma-butyrolactones and gamma-butyrolactams with aldehydes under basic conditions. Different bases and solvents were screened in the context of generating gamma-butyrolactones. Diastereoselectivity was observed and gamma-butenolides and gamma-butyrolactams showed opposite diastereoselectivity under the same reaction condition.

Multinuclear enantiopure titanium self‐assembly complexes—synthesis, characterization and application to organic synthesis

AbstractHexa‐ and nonanuclear titanium complexes were obtained by self‐assembly of titanium(IV)‐tert‐butoxide and D‐mandelic acid. Suitable single crystals of these complexes were characterized by X‐ray structure analysis. When used with these complexes, aldol adducts were isolated with a high degree of regioselectivity in direct aldol additions of aromatic and aliphatic aldehydes to functionalized unsymmetrical ketones. High syn‐diastereoselectivities were obtained in aldol additions of enolizable aldehydes with hydroxyacetone and methoxyacetone. Copyright © 2007 John Wiley & Sons, Ltd.

Brønsted Acids as Additives for the Direct Asymmetric Aldol Reaction Catalyzed by l-Prolinethioamides. Direct Evidence for Enamine−Iminium Catalysis

The use of protonated l-prolinethioamide instead of the free base derivative 1 as the organocatalyst for the direct aldol addition has a profound and appreciable effect on both the yield and the stereochemical course of the reaction. 4-Nitrobenzaldehyde (2) reacts with acetone in the presence of the protonated catalyst 1.TFA, affording aldol product 3 with a yield up to 99% and an ee up to 98%. The catalyst loading can be lowered to 2.5 mol %. More than 20 different acids were investigated as an additive, and its role as cocatalyst has been discussed. Furthermore, reactions of l-prolinethioamide salts with acetone have been monitored using ESI-MS and 1H NMR techniques, giving insight into the mechanism of the direct aldol reaction. The presumed formation of the iminium salt 10 has been unambiguously confirmed.

A Direct Aldol Addition of Simple Thioesters Employing Soft Enolization

Simple thioesters undergo direct aldol addition to aldehydes in the presence of magnesium bromide-diethyl ether and N,N-diisopropylethylamine using untreated, reagent grade dichloromethane under atmospheric conditions. The reactions proceed extremely rapidly and in excellent yield.

Direct Asymmetric Aldol‐Tishchenko Reaction

AbstractThe asymmetric direct aldol reaction of nonpreactivated substrates constitutes one of the most powerful tools in current synthetic chemistry. In the last few years, chiral metal complexes have been found to catalyze the direct aldol addition of unmodified ketones to aldehydes with both high efficiency and selectivity. However, many problems have to be overcome in this still young field of chemistry. The most challenging aspect of this chemistry is the substrate limitation of known catalysts. In this field, the asymmetric aldol‐Tishchenko reaction can be regarded as a parallel methodology that expands the scope of possible applications. In the aldol‐Tishchenko reaction, two aldehyde molecules undergo addition to form an aldol adduct, which is subsequently reduced by a third aldehyde to yield 1,3‐diol monoesters through a [3,3]‐bond reorganization. With the use of aldehydes and ketones in the aldol‐Tishchenko reaction, diols with three adjacent stereogenic centers can be created in one single operation. Thus, the reaction can be regarded as an extremely atom efficient method for the construction of enantiomerically enriched products that can serve as fundamental building blocks in synthesis. Moreover, the aldol‐Tishchenko condensation is nowadays the most efficient methodology available for the direct catalytic asymmetric aldol reaction of methylene ketones. This article provides a synopsis of this field and highlights some of the challenges that still remain.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A Facile and Efficient Direct Aldol Addition of Simple Thioesters.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Unusual Highly Regioselective Direct Aldol Additions with a Moisture‐Resistant and Highly Efficient Titanium Catalyst.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

A Facile and Efficient Direct Aldol Addition of Simple Thioesters

[reaction: see text] Simple thioesters undergo direct aldol addition to aldehydes in the presence of MgBr(2).OEt(2) and i-Pr(2)NEt using untreated, reagent-grade CH(2)Cl(2) under atmospheric conditions. The reactions proceed extremely rapidly and in excellent yield.

Unusual Highly Regioselective Direct Aldol Additions with a Moisture-Resistant and Highly Efficient Titanium Catalyst

[reaction: see text] The extremely robust and water-stable tetranuclear complex Ti(4)(mu-BINOLato)(6)(mu(3)-OH)(4) was found to catalyze the direct aldol addition with high regioselectivities at the more steric alpha-encumbered side of unsymmetrical ketones. As few as 0.2 mol % loadings with this cluster were enough to afford complete conversions. The reaction proceeds very smoothly without a significant amount of byproducts. The formation of quaternary stereocenters is described.

Amino Acid Catalyzed Dynamic Kinetic Asymmetric Transformations (DYKAT): One‐Step de novo Synthesis of Polyketide Sugars from Racemic β‐Hydroxy Aldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Amino acid-catalyzed dynamic kinetic asymmetric transformations (DYKAT): one-step de novo synthesis of polyketide sugars from racemic β-hydroxy aldehydes

The ability of amino acids to catalyze dynamic kinetic asymmetric transformation (DYKAT) with excellent stereoselectivity is presented. The novel DYKAT process was applied in the proline-catalyzed one-step de novo synthesis of triketide- and deoxysugars, which were formed with excellent diastereoselectivity and up to 99% ee. The de novo synthesis is accomplished via an enzyme-like DYKAT process, which includes continuous amino acid-mediated racemization of the acceptor β-hydroxy aldehyde in combination with amino acid-catalyzed direct selective aldol addition.