R-3-methyl-γ-butyrolactone as a template for the synthesis of (+)-invictolide

The dextrorotatory antipode of the pheromone invictolide has been synthesized from R-3-methyl-γ-butyrolactone, which is employed as a stereochemical template for the addition of propionate units via a Claisen rearrangement and a palladium-catalyzed alkylation. (+)-Invictolide is inactive.     

Enantioselective formal synthesis of (−)-ovalicin using quinic acid as a chiral template

The key intermediate 18 for the synthesis of (−)-ovalicin was synthesized using (−)-quinic acid as the chiral source, through a series of stereocontrolled and efficient chemical reactions, thus establishing a new, formal synthesis of the natural target. The featuring spirocyclic epoxide function has been installed by internal Williamson ether synthesis using the functionalities originally present at C-1 of (−)-quinic acid after the appropriate adjustments required to introduce the necessary functionality at C-2.     

Asymmetric synthesis of 3-butylphthalide using isomannide and isosorbide as chiral auxiliaries

A new approach for asymmetric syntheses of (S) and (R)-3-n-butylphthalide (NBP) is presented.The diastereoselective addition of dibutylzinic to aromatic aldehyde 10 or 11 generated from isomannide-or isosorbide-derived chiral auxiliary afforded S-NBP or R-NBP in high optical yields.     

Studies on the synthesis of chiral nonracemic 3,4-disubstituted azepanes,a formal synthesis of (+)- and (−)-balanol

Sugar lactones were converted to 3,4-disubstituted azepanes and caprolactam derivatives by selective deoxygenation, functionalization and reductive cyclization. The cyclization proved troublesome with 6-azidolactols but led to good results with the corresponding lactones. A formal synthesis of (+)- and (−)-balanol is reported.     

Stereoselective synthesis of C-alkyl and functionalised C-alkyl glycosides using ‘thiophene’ as a masked C-4 synthon

Synthesis of C-alkyl and functionalised C-alkyl glycosides is achieved by desulphurisation of the corresponding thiophene glycosides, wherein ‘thiophene’ is utilised as a masked four-carbon synthon. Thiophene glycosides in turn were prepared from the corresponding sugar lactols.     

Formal synthesis of (−)-stemoamide using a useful epimerization at C-8

The formal synthesis of (?)-stemoamide was achieved starting from l-pyroglutamic acid. The key steps used are the allylation using BF₃·OEt₂, ring closing metathesis, allylic oxidation and a novel epimerization at C8.     

( S )-(?)-α-Methylbenzylamine as chiral auxiliary in the synthesis of (+)-lortalamine

Abstract  

(+)-Lortalamine was synthesised using (S)-(−)-α-methylbenzylamine as a chiral auxiliary. The stereochemistry of an intermediate compound was established on the basis of X-ray crystallography, allowing unambiguous assignment of the absolute configuration.     

(+)-δ-Cadinol as a promising starting compound in the synthesis of eleuthesides

Russian Chemical Bulletin -     

Asymmetric synthesis of quaternary α-amino acids using d-ribonolactone acetonide as chiral auxiliary

We describe a new simple methodology to prepare enantiopure α,α-dialkylglycines based on the use of commercially available d-ribonolactone as a chiral auxiliary. Enantiopure α-methyl and α-butyl series are prepared through diastereoselective alkylation and subsequent Schmidt rearrangement of α,α-dialkylacetoacetates of d-ribonolactone acetonide. Absolute configuration was assigned through preparation of enantiopure 4,4-disubstituted 3-methyl-2-pyrazolin-5-ones.     

Stereoselective synthesis of protected threo-β-hydroxy-l-glutamic acid using a chiral aziridine

Threo-β-hydroxy-l-glutamic acid derivatives with different carboxylic acid protecting groups were stereoselectively prepared from a chiral aziridine-2-carboxylate using an aldol reaction, stereoselective ketone reduction, and aziridine ring transformation.     

Formal total synthesis of (±)-bisabolangelone by using a radical cyclization

A photoreductive cyclization has been used to synthetize the bicyclic core of (±)-bisabolangelone.     

Preparation of new chiral pyrrolidinebisphosphines as highly effective ligands for catalytic asymmetric synthesis of R-(−)-pantolactone

New chiral pyrrolidinebisphosphines, MSCPM, PCPM and BCPM, were prepared. Among them, BCPM was found to be the most effective ligand for catalytic asymmetric synthesis of R-(−)-pantolactone.     

Formal synthesis of (+)-lactacystin based on a novel radical cyclisation of an α-ethynyl substituted serine

A diastereoselective 5-exo-dig radical cyclisation of the bromoamide 7 produced from the enantiopure α-ethynyl substituted amino alcohol 5 led to the pyrrolidinone 8 (2:1 α:β epimers) in 70% yield. Oxidative cleavage of the alkene bond in 8, followed by a stereoselective α-methylsulfanylation of the resulting 4-keto derivative 9, next led to the methylsulfanyl derivative 10. Finally, the pyrrolidinone derivative 10 was converted into the key intermediate 12 used previously in an enantioselective synthesis of (+)-lactacystin.     

(<Emphasis Type="Italic">S</Emphasis>)-(−)-α-Methylbenzylamine as chiral auxiliary in the synthesis of (+)-lortalamine

Abstract  (+)-Lortalamine was synthesised using (S)-(−)-α-methylbenzylamine as a chiral auxiliary. The stereochemistry of an intermediate compound was established on the basis of X-ray crystallography, allowing unambiguous assignment of the absolute configuration. Graphical abstract        

Diphenylparabanic acid as a synthon for the synthesis of α-diketones and α-ketocarboxylic acids

Diphenylparabanic acid was found to react with >2 equiv of organolithiums at -78 °C to effectively give the corresponding symmetrical α-diketones. However, upon treatment with 1 equiv of organolithium, the parabanic acid gave mainly 5-substituted 5-hydroxyimidazolidine-2,4-diones. On the other hand, Grignard reagents were less reactive toward the parabanic acid at low temperature, and selectively gave the corresponding 5-hydroxyimidazolidine-2,4-diones even if more than 1 equiv of the reagents was used. A tandem process in which the parabanic acid was first reacted with a Grignard reagent and then reacted in one-pot with an organolithium effectively gave the unsymmetrical α-diketone. 5-Substituted 5-hydroxyimidazolidine-2,4-diones were useful as versatile precursors for preparing α-ketocarboxylic acids as well as unsymmetrical α-diketones.     

Total synthesis of (+)-nafuredin-γ using a highly stereoselective Ti-mediated aldol reaction

An efficient total synthesis of (+)-nafuredin-γ has been achieved in 10 steps from (E)-3-(tributylstannyl)propenal. The synthesis features direct construction of an anti-1,2-diol moiety via a Ti-mediated aldol reaction of lactyl derivative and rapid fragment assembly, which relied on well-established Pd chemistry.     

A total synthesis of (±)-α-cyclopiazonic acid using a cationic cascade as a key step

The indole alkaloid α-cyclopiazonic acid 1 has been synthesised by a route, which features at its core an acid-catalysed cationic cascade cyclisation terminated by a sulfonamide group.     

Asymmetric synthesis of the C1–C6 portion of the psymberin using an Evans chiral auxiliary

The C1–C6 region of the potent cytotoxic agent psymberin has been synthesized. The key transformations of the synthesis are an auxiliary-controlled addition of a Sn(II)-glycolate enolate to an aldehyde to yield the anti-aldol product and transforming the primary alcohol into a terminal olefin utilizing organoselenium chemistry.