Aldol Coupling Reaction Research Articles

Valmet Chiral Schiff‐Base Ligands And Their Copper(II) Complexes as Organo, Homogeneous and Heterogeneous Catalysts for Henry, Cyanosilylation and Aldol Coupling Reactions

AbstractCyanosilylation, aldol coupling and asymmetric Henry reactions were carried out with L‐ and D‐valmet ligands in different configurations: i) coordinated to sodium ions, as organocatalysts, with week base properties, ii) complexes with copper(II), as homogeneous catalysts, and iii) immobilized copper(II) complexes onto graphene oxide (GO) as heterogeneous catalysts. For the reaction of benzaldehyde and nitromethane in water these afforded an asymmetric Henry reaction, with a spectacular increase of the conversion and ee (92.5 and 95.8 %, respectively) after the deposition on GO. Ligand complexed copper was also effective for cyanosilylation and Aldol coupling reaction.

Stereoselective Convergent Synthesis of Carbon Skeleton of Cotylenin A Aglycone

AbstractIn this paper, the synthesis of the carbon skeleton of cotylenin A aglycone is described. The key reactions, including an intramolecular aldol reaction, an aldol coupling reaction, and a ring-closing meta­thesis, allow for the effective and stereoselective access to the carbon skeleton of cotylenin A aglycone. The stereochemistry was confirmed by single-crystal X-ray crystallographic analyses of related compounds.

Chemical and Biochemical Approaches for the Synthesis of Substituted Dihydroxybutanones and Di- and Tri-Hydroxypentanones.

Polyhydroxylated compounds are building blocks for the synthesis of carbohydrates and other natural products. Their synthesis is mainly achieved by different synthetic versions of aldol-coupling reactions, catalyzed either by organocatalysts, enzymes, or metal-organic catalysts. We have investigated the formation of 1,4-substituted 2,3-dihydroxybutan-1-one derivatives from para- and meta-substituted phenylacetaldehydes by three distinctly different strategies. The first involved a direct aldol reaction with hydroxyacetone, dihydroxyacetone, or 2-hydroxyacetophenone, catalyzed by the cinchona derivative cinchonine. The second was reductive cross-coupling with methyl- or phenylglyoxal promoted by SmI2, resulting in either 5-substituted 3,4-dihydroxypentan-2-ones or 1,4 bis-phenyl-substituted butanones, respectively. Finally, in the third case, aldolase catalysis was employed for synthesis of the corresponding 1,3,4-trihydroxylated pentan-2-one derivatives. The organocatalytic route with cinchonine generated distereomerically enriched syn-products (de = 60-99%), with moderate enantiomeric excesses (ee = 43-56%) but did not produce aldols with either hydroxyacetone or dihydroxyacetone as donor ketones. The SmI2-promoted reductive cross-coupling generated product mixtures with diastereomeric and enantiomeric ratios close to unity. This route allowed for the production of both 1-methyl- and 1-phenyl-substituted 2,3-dihydroxybutanones at yields between 40-60%. Finally, the biocatalytic approach resulted in enantiopure syn-(3 R,4 S) 1,3,4-trihydroxypentan-2-ones.

Highly Selective Formation of n-Butanol from Ethanol through the Guerbet Process: A Tandem Catalytic Approach.

A highly selective (>99%) tandem catalytic system for the conversion of ethanol (up to 37%) to n-butanol, through the Guerbet process, has been developed using a bifunctional iridium catalyst coupled with bulky nickel or copper hydroxides. These sterically crowded nickel and copper hydroxides catalyze the key aldol coupling reaction of acetaldehyde to exclusively yield the C4 coupling product, crotonaldehyde. Iridium-mediated dehydrogenation of ethanol to acetaldehyde has led to the development of an ethanol-to-butanol process operated at a lower temperature.

Synthesis of the C7-26 Fragment of Amphidinolides G and H

A new approach to the synthesis of the C7-26 fragment of amphidinolides G and H was developed. In the sequence, the C7-18 portion of this fragment was synthesized using an acetylide coupling protocol, while an Evans alkylation and Sharpless asymmetric dihydroxylation were employed as key steps in construction of the C19-26 subfragment. Finally, both of these units were joined by utilizing an aldol coupling reaction to produce the target C7-26 fragment in good yield.

Felkin–Anh selectivity in Rh(bisoxazolinylphenyl)-catalyzed reductive aldol coupling reaction: asymmetric synthesis of stereotriads

The catalytic reductive aldol coupling of 2-phenylpropionaldehyde and acrylate derivatives with rhodium-bisoxazolinyl catalysts resulted in high Felkin–Anh selectivity (β,γ- syn) up to 98% accompanied by α,β- anti diastereoselectivity and high enantiomeric excesses up to 99%.

Racemic and asymmetric cobalt-catalysed reductive aldol couplings of α,β-unsaturated amides with ketones

In the presence of diethylzinc as a stoichiometric reductant, substoichiometric quantities of an appropriate cobalt source catalyse diastereoselective reductive aldol coupling reactions of α,β-unsaturated amides with ketones. The use of a readily available oxazolidine as a chiral auxiliary imparts high levels of asymmetric induction in these reactions.

Asymmetric synthesis of α-chiral dihydrocinnamates by catalytic reductive aldol coupling and subsequent dehydroxylation

Optically active dihydrocinnamate derivatives bearing the chiral carbon center at α-position were synthesized by Rh(Phebox)-catalyzed asymmetric reductive aldol coupling reaction with substituted cinnamates and benzaldehyde derivatives and subsequent dehydroxylation reaction.

‘GaI’: A new reagent for chemo- and diastereoselective C–C bond forming reactions

The potential of ‘GaI’ as a reductant in organic transformations, in particular C–C bond forming reactions involving α-functionalised ketones, has been investigated. Of most interest are the diastereoselective aldol coupling reactions of the α-alkoxy ketones, PhC(O)C(H)(OR)Ph, R = Me, Et or iPr, which give the novel γ-alkoxy, β-hydroxy ketones, PhC(O)C(H)(Ph)C(OH)(Ph)C(H)(OR)Ph, containing three contiguous stereogenic centres. The diastereostereoselectivity of these reactions was established from NMR spectroscopic and X-ray crystallographic studies of the products. When R = Me, the 2R,3S,4R/2S,3R,4S-enantiomeric pair is formed, whereas when R = Et or iPr, 2R, 3R, 4S/2S, 3S, 4R-diastereoisomers result. These differences are rationalised in terms of the likely transition states of the reactions. The same products are not formed when higher oxidation salts of gallium, or InI, are employed as the inorganic reagent. The reactivity of “GaI” towards α-halo ketones, a 1,2-diketone and α,β-unsaturated ketones has also been explored. Again, the outcomes of these reactions have been compared to those involving Ga(II) and Ga(III) reagents.

The First Total Synthesis of the Diastereoisomers A and B ofTuxpanolidefromPerymenium hintonii

The first total synthesis of the diastereoisomers A and B of the natural product Tuxpanolide have been achieved through the stereo-controlled construction of optically active β-hydroxyl-y-butyrolactones, the aldol coupling, dehydration and deprotection reaction with the p-TsOH as the key steps.

Diastereoselective aldol reactions with butane-2,3-diacetal protected glyceraldehyde derivatives

Diastereoselective aldol coupling reactions with butane-2,3-diacetal (BDA) protected glyceraldehyde derivatives are reported. Good selectivities of up to 20:1 for the homologated aldol products have been achieved in preparatively useful yields.

Total synthesis of zaragozic acid C by an aldol-based strategy

A total synthesis of zaragozic acid C by a convergent strategy is described in which the key features include (1) the simultaneous creation of the C4 and C5 quaternary stereogenic centers by a Sn(OTf) 2-promoted aldol coupling reaction between an α-keto ester and a silyl ketene thioacetal derived from l- and d-tartaric acids, respectively, (2) the direct introduction of lithium acetylide as the C1 side chain equivalent onto the fully functionalized aldehyde, and (3) construction of the bicyclic core structure by acid-catalyzed internal ketalization under kinetically controlled conditions.

Total Synthesis of the Squalene Synthase Inhibitor Zaragozic Acid C

Zaragozic acids and squalestatins were documented by Merck, Glaxo, and Tokyo Noko University/Mitsubishi Kasei Corporation as part of a program aimed at identifying novel inhibitors of squalene synthase, as well as farnesyl transferase. These natural products have attracted considerable attention from numerous synthetic chemists because of their therapeutic potential and novel architecture. This review highlights our total syntheses of zaragozic acid C by two convergent strategies. The key steps in our first-generation synthesis involve 1) simultaneous creation of the C4 and C5 quaternary stereocenters through the Sn(OTf)2-promoted aldol coupling reaction between the alpha-keto ester and silyl ketene thioacetal derived from L- and D-tartaric acids, respectively; and 2) construction of the bicyclic core structure via acid-catalyzed internal ketalization under kinetically controlled conditions. The second-generation strategy relies on a tandem carbonyl ylide formation/1,3-dipolar cycloaddition approach and features elongation of the C1 alkyl side chain through an olefin cross-metathesis as well as high convergency and flexibility.

Diastereoselective Additions of Nucleophiles to α-Acetoxy Ethers Using the α-(Trimethylsilyl)benzyl Auxiliary

We report the diastereoselective addition of a variety of nucleophiles to alpha-(trimethylsilyl)benzyl-substituted oxocarbenium ions. The oxocarbenium ions are generated from alpha-acetoxy ethers, which are easily prepared via reductive acetylation of esters. The alpha-(trimethylsilyl)benzyl auxiliary produces good to excellent facial selectivity with a variety of nucleophiles, including silyl enol ethers, silyl ketene acetals, allylsilanes, and crotylsilanes. The utility of this auxiliary is further demonstrated in a complex ketone aldol coupling reaction. [reaction: see text]

Formal synthesis of (+)-discodermolide.

[structure: see text] Herein we report the formal total synthesis of (+)-discodermolide in 21 steps (longest linear sequence) from commercially available Roche ester. This synthesis features the assembly of C(9-18) and C(19-24) fragments via a metal-chelated aldol coupling reaction.

Synthesis of a C(1)-C(14)-containing fragment of callipeltoside A.

[formula: see text] A C(1)-C(14)-containing fragment of callipeltoside A (1, Scheme 1) was synthesized efficiently via a dianion aldol coupling reaction between aldehyde 2 and ketoester 3. A surprising lack of reactivity between the alkenes in 13 and the Grubbs initiator 15 was encountered. An equally surprising rate acceleration of the reaction between 15 and allylic alcohols (alk-1-en-3-ols) as well as their subsequent cleavage to methyl ketones was discovered. In situ 1H NMR analysis has proven to be a very useful tool for monitoring RCM reactions of complex substrates such as 13.

Synthesis of the C19 through C27 segment of okadaic acid using vinylogous urethane aldol chemistry: Part III

The synthesis of the C-19 through C-27 segment of the marine natural product okadaic acid was accomplished employing a highly enantio- and diasteroselective aldol coupling reaction of a chiral vinylogous urethane lactone enolate. The remainder of the carbon skeleton of this segment was constructed by a diastereoselective γ-oxygenated allylstannane addition. Formation of the tetrahydropyran ring was achieved utilizing a stereoselective electrophilic cyclization.

Bifunctional Condensation Reactions of Alcohols on Basic Oxides Modified by Copper and Potassium

Alcohol dehydrogenation and condensation reactions are involved in chain growth pathways on Cu/MgCeOxpromoted with potassium. These pathways lead to the formation of isobutanol with high selectivity via reactions of higher alcohols with methanol-derived C1species in reaction steps also relevant to higher alcohol synthesis from CO/H2mixtures at higher pressures on K–Cu/MgCeOxcatalysts. Ethanol reactions on K–CuyMg5CeOxshow that both Cu and basic sites participate in alcohol dehydrogenation and aldol condensation steps leading to n-butyraldehyde and acetone. Chain growth occurs by condensation reactions involving a metal-base bifunctional aldol-type coupling of alcohols. Reactions of12C2H5OH–13C2H4O mixtures show that direct condensation reactions of ethanol can occur without requiring the intermediate formation of gas phase acetaldehyde. Reactions of C2H5OH/D2mixtures show that Cu sites increase the rate of aldol condensation by introducing recombinative desorption sites that remove hydrogen atoms formed in C–H activation steps leading to the unsaturated aldol-type species required for chain growth. Reactions of acetaldehyde and13C-labeled methanol lead predominantly to 1-13C-propionaldehyde and 2-13C-isobutyraldehyde, both of which lead to isobutanol during CO/H2reactions. Mixtures of propionaldehyde and13C-labeled methanol lead to singly-labeled isobutyraldehyde. Chain growth to C2+alcohols occurs via addition of a methanol-derived C1species to adsorbed oxygen-containing intermediates. The gradual appearance of13C in the unlabeled reactant within these mixtures shows that aldol coupling reactions are reversible. Reverse aldol condensation reactions after intramolecular hydride transfer lead to the formation of acetone from ethanol. Isobutyraldehyde is a preferred end-product of aldol-type chain growth reactions of alcohols because it lacks the two α-hydrogens required for subsequent chain growth.

Studies in marine macrolide synthesis: Synthesis of the C 1C 15 subunit of spongistatin 1 (altohyrtin A) and 15,16- anti aldol coupling reactions

The C 1C 15 aldehyde 3, containing the AB-spiroacetal of spongistatin 1 ( 1), was prepared in 17 steps from methyl ketone ( S)-8. The C 15 and C 16 stereocentres could be introduced together, relying on Felkin-Anh control, by using a boron-mediated, anti aldol coupling reaction, as in 22 → 25 and 26.

Total Synthesis of the Squalene Synthase Inhibitor Zaragozic Acid C

The total synthesis of zaragozic acid C has been achieved by a convergent strategy, wherein the key feature of the construction of 2,8-dioxabicyclo[3.2.1]octane core structure is a simultaneous creation of the C4 and C5 quaternary carbon centers by Sn(OTf)2-promoted aldol coupling reaction between α-keto ester and silyl ketene thioacetal derived from L- and D-tartaric acids, respectively.