Stereoselective Aldol Reaction Research Articles

ChemInform Abstract: Asymmetric Total Synthesis of Epolactaene

A total synthesis of the neuritegenic agent, epolactaene has been achieved via a convergent approach in 14 steps from optically active lactaldehyde derivatives. The key steps include (i) the stereoselective aldol reaction between malonate ester enolate and α-alkoxy aldehyde (ii) diastereospecific lactonization of malonate ester (iii) E-selective Wittig reaction. The optical rotation was identical with that of the natural (+) -epolactaene, which establishes that the absolute configuration of natural (+) -epolactaene is (13R, 14R) definitively. Other several epoxy-γ-lactam compounds also synthesized which suggest this method would be general for organic synthesis.

Total synthesis of auripyrone B using a non-aldol aldol-cuprate opening process.

A non-aldol aldol-cuprate opening generates the polypropionate 11 from the epoxy ether 14 in eight steps as a single diastereomer. A highly stereoselective aldol reaction of 8 with 9 gives the aldol product 7 in high yield and excellent diastereoselectivity, due to double stereodifferentiation. This compound was used for an efficient synthesis of the natural product auripyrone B 2 in only 20 steps and 8% overall yield from 14 using a late-stage spiroketalization onto a stable hemiketal as the final key step.

ChemInform Abstract: Stereoselective Aldol Reaction of Glutarimides Using Pseudo C2 Symmetry.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Stereoselective Aldol Reaction of Glutarimides Using Pseudo C2 Symmetry

Stereoselective Aldol Reaction of Glutarimides Using Pseudo <i>C</i>₂ Symmetry

Evaluation of retro-inverso modifications of HTLV-1 protease inhibitors containing a hydroxyethylamine isoster

Effects of retro-inverso (RI) modifications of HTLV-1 protease inhibitors containing a hydroxyethylamine isoster backbone were clarified. Construction of the isoster backbone was achieved by a stereoselective aldol reaction. Four diastereomers with different configurations at the isoster hydroxyl site and the scissile site substituent were synthesized. Inhibitory activities of the new inhibitors suggest that partially modified RI inhibitors would interact with HTLV-1 protease in the same manner as the parent hydroxyethylamine inhibitor.

Stereoselective total synthesis of (+)-polyrhacitide A

A facile stereoselective total synthesis of secondary metabolite (+)-polyrhacitide A is described. Stereoselective aldol reaction, Horner–Wardsworth–Emmons reaction, Evans acetal intramolecular oxa-Michael reaction and diastereoselective syn reduction reaction are the key steps involved in the target synthesis.

Stereoselective Aldol Reaction of Glutarimides Using PseudoC2Symmetry

The boron aldol reaction of beta-substituted glutaric imides bearing an oxazolidinone-based auxiliary proceeds with excellent diastereoselectivity; switching the tertiary amine employed between i-Pr(2)EtN or Et(3)N affords enantiomeric lactone product.

Synthesis of Furanoid Amino Acids via a Domino Michael-Aldol-Addition-Cyclization Approach

Chelated enolates undergo Michael addition towards halogenated α,β-unsaturated esters m a highly stereoselective fashion. The enolates formed can be trapped with aldehydes in a stereoselective aldol reaction, before subsequent cyclization gives rise to substituted furanoid amino acids. Up to for stereogenic centers can be formed in this new one-pot reaction.

ChemInform Abstract: Highly Stereoselective Aldol Reactions in the Total Syntheses of Complex Natural Products

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.

Total syntheses of (+)-tedanolide and (+)-13-deoxytedanolide.

Convergent total syntheses of the potent cytotoxins (+)-tedanolide (1) and (+)-13-deoxytedanolide (2) are described. The carbon framework of these compounds was assembled via a stereoselective aldol reaction that unifies the C(1)-C(12) ketone fragment 5 with a C(13)-C(23) aldehyde fragment 6 (for 13-deoxytedanolide) or 52 (for tedanolide). Multiple obstacles were encountered en route to (+)-1 and (+)-2 that required very careful selection and orchestration of the stereochemistry and functionality of key intermediates. Chief among these issues was the remarkable stability and lack of reactivity of hemiketals 33b and 34 that prevented the tedanolide synthesis from being completed from aldol 4. Key to the successful completion of the tedanolide synthesis was the observation that the 13-deoxy hemiketal 36 could be oxidized to C(11,15)-diketone 38 en route to 13-deoxytedanolide. This led to the decision to pursue the tedanolide synthesis via C(15)-(S)-epimers, since this stereochemical change would destabilize the hemiketal that plagued the attempted synthesis of tedanolide via C(15)-(R) intermediates. However, use of C(15)-(S)-configured intermediates required that the side-chain epoxide be introduced very late in the synthesis, owing to the ease with which the C(15)-(S)-OH cyclized onto the epoxide of intermediate 50.

Stereoselective aldol reaction catalyzed by a highly recyclable polystyrene supported substituted prolinamide catalyst

Polystyrene supported substituted prolinamide was used as catalyst in the aldol reaction between cyclohexanone or acetone and several substituted benzaldehydes in chloroform/water. This catalyst afforded aldol products in high yields and stereoselectivities, especially in the case of reactions performed with acetone. The catalyst was easily recovered by filtration and reused, after regeneration with formic acid, up to 22 times.

Efficient stereoselective synthesis of enantiopure 2-substituted paraconic acids

Eight enantiopure (2 S,3 S)-2-aryl-5-oxotetrahydrofuran-3-carboxylic acids have been synthesized. The key step was a highly stereoselective aldol reaction between an N-acyl oxazolidinone and a corresponding aldehyde.

Facile Synthesis of γ‐Alkylidenebutenolides.

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.

Studies directed towards the total synthesis of botcinic acid, the revised structure of botcinolide: synthesis of the highly substituted tetrahydropyran moiety

Synthesis of the highly substituted polyoxygenated tetrahydropyran ring of botcinic acid, the revised structure of botcinolide is achieved using, as key steps, a highly stereoselective aldol reaction of the titanium enolate from a lactate-derived chiral ketone and a stereoselective dihydroxylation.

Synthesis of RK-397

RK-397 possesses antifungal, antitumor and antibacterial activity. Stereoselective aldol reactions, hydroxyl-directed reductions and allylborations were used to create most of the stereo­centers in the polyol portion of the target. Markworthy features include the cross-metathesis of heptatrienal and fragment A to initiate construction of the polyene fragment and the 1,5-asymmetric induction used to fashion fragment D.

Studies directed towards the total synthesis of lycoperdinosides: stereoselective construction of the C1–C9 and C10–C21 segments of the molecules

The three chiral centres of the C1–C9 moiety of the six-membered lactone glycosides, lycoperdinosides A and B, have been derived from a common starting material containing a single chiral centre. In contrast, the C10–C21 segment of these molecules has been synthesized using, as key steps, a highly stereoselective aldol reaction, a Ti(III)-mediated opening of a trisubstituted epoxy alcohol and an efficient directed hydrostannylation of a suitably substituted internal alkyne.

Stereoselective Tandem Reductive Aldol Reaction

Stereoselective Tandem Reductive Aldol Reaction

Total synthesis of erythromycin B

We report the details of the first total synthesis of erythromycin B using two different strategies for the end game. The first of these follows a classical approach in which the desosamine and cladinose residues are sequentially appended to a macrocyclic lactone, which was formed by cyclization of a seco acid derivative, to give a bis-glycosylated macrolide intermediate that is converted into erythromycin B. The second strategy features an abiotic approach in which a seco acid bearing a desosamine residue is cyclized to give a monoglycosylated macrocyclic lactone that is then transformed into erythromycin B via a sequence of steps involving refunctionalizations and a glycosylation to introduce the cladinose moiety. Attempts to prepare a bis-glycosylated seco acid by de novo synthesis were unsuccessful. The syntheses of the key seco acid intermediates feature the oxidative transformation of a furan containing C(3)–C(10) to provide a dioxabicyclo[3.3.1]nonenone that served as a template on which to create the stereocenters at C(6) and C(8). A stereoselective aldol reaction was used to establish the C(11)–C(15) segment, and a stereoselective crotylation was implemented to introduce the propionate subunit comprising C(1)–C(2).

Expedient Stereoselective Synthesis of Coronafacic Acid Through Intramolecular Diels−Alder Cyclization

A stereoselective synthesis of coronafacic acid, a natural component of the phytotoxin coronatin, was achieved using an intramolecular Diels-Alder reaction as the key step. The triene precursor bearing a substituted diene and a vinylketone as dienophile was synthesized and then tested in the thermal intramolecular cyclization. We have devised a new strategy to assemble the E,Z-diene through the stereoselective aldol reaction of an ester enolate followed by a stereoselective dehydration. Following the thermal cyclization, the corresponding hydrindanone thereby obtained with the desired relative stereochemistry could easily be converted into the natural product. The synthesis of the coronafacic acid was accomplished in six steps in 29% overall yield.

Stereoselective Aldol Reactions Catalyzed by Acyclic Amino Acids in Aqueous Micelles

AbstractThe catalytic properties of all proteinogenic, acyclic amino acids for direct aldol reaction in H2O, assisted by various surfactants, were investigated. The basic and neutral amino acids were shown to be efficient catalysts, giving rise to good‐to‐excellent yields of adducts (up to 95%), with moderate‐to‐good diastereoselectivities (up to 86%), L‐arginine being the most‐effective catalyst. The syn/anti diastereoisomer ratio could be readily tuned by proper choice of the amino acid used. Also, the range of substrates that underwent the reaction was extended to less‐reactive aldehydes carrying electron‐donating Br substituents.