A concise enantioselective synthesis of the fungal metabolite (+)-decarestrictine L

A stereoselective 10-step synthesis of the fungal metabolite (+)-decarestrictine L from commercially available ethyl (R)-3-hydroxybutyrate is described in which tandem oxonium ylide formation and rearrangement is used to construct the tetrahydropyranyl core of the natural product.     

A short synthesis of (+)-harzialactone A and (R)-(+)-4-hexanolide via proline-catalyzed sequential α-aminooxylation and Horner–Wadsworth–Emmons olefination of aldehydes

An efficient and short enantioselective synthesis of the antitumor marine metabolite, (+)-harzialactone A 1 and pheromone, (R)-(+)-4-hexanolide 2 using l-proline-catalyzed sequential α-aminooxylation and Horner–Wadsworth–Emmons olefination of the respective aldehydes is described.     

Short and practical enantioselective synthesis of linezolid and eperezolid via proline-catalyzed asymmetric α-aminooxylation

An efficient enantioselective synthesis of the antibacterials, linezolid (U-100766), and eperezolid (U-100592) using d-proline-catalyzed asymmetric α-aminooxylation of aldehydes as the key step is described here. This is the first report on the enantioselective synthesis of linezolid and eperezolid using asymmetric catalysis.     

A concise enantioselective synthesis of (+)-lentiginosine

A high yielding enantioselective synthesis of the indolizidine alkaloid, (+)-lentiginosine, has been described based on asymmetric aza-Cope rearrangement and the l-proline catalyzed α-aminooxylation of aldehydes. The strategy also makes use of ring-closing metathesis for the construction of piperidine core.     

A concise enantioselective synthesis of (+)-febrifugine

A short enantioselective synthesis of (+)-febrifugine, a potent antimalarial alkaloid, has been described based on the regioselective asymmetric dihydroxylation of a 1,4-dienic ester as the key step. The strategy also involves chemoselective [3,3]-sigmatropic rearrangement of 1,5-hexadiene-3-ol and intramolecular lactamization of azidolactone for the construction of piperidine core.     

Design and Synthesis of New α-hydroxy β-fluoro/β-trifluoromethyl and Unsaturated Phosphonates from Carbohydrate-Derived Building Blocks via Pudovik and Horner–Wadsworth–Emmons Reactions

Herein, we present the application of fluorinated carbohydrate-derived building blocks for α-hydroxy β-fluoro/β-trifluoromethyl and unsaturated phosphonates synthesis. Pudovik and Horner–Wadsworth–Emmons reactions were applied to achieve this goal. The proposed pathway of the key reactions is supported by the experimental results, as well as quantum chemical calculations. The structure of the products was established by spectroscopic (1D, 2D NMR) and spectrometric (MS) techniques. Based on our data received, we claim that the progress of the Pudovik and HWE reactions is significantly influenced by the acidic protons present in the molecules as assessed by pK_a values of the reagent.     

A short enantioselective synthesis of the antiepileptic agent, levetiracetam based on proline-catalyzed asymmetric α-aminooxylation

An efficient enantioselective synthesis of a new antiepileptic drug, levetiracetam is described, in high optical purity (>99.5% ee), using proline-catalyzed α-aminooxylation of n-butyraldehyde as the key step.     

Metal-mediated dearomatization leading to 2-azaspiro[4.5]decanes via tandem nucleophilic aromatic addition–Horner–Wadsworth–Emmons olefination–oxidative demetalation sequences

A ruthenium-mediated dearomatization sequence has been developed that delivers structurally intriguing azaspirolactam products in stereoselective fashion. Treatment of (η⁶-arene)Ru(cyclopentadienyl) complexes bearing N-benzyl-β-amido phosphonate side chains with excess NaH results in intramolecular nucleophilic aromatic addition to the ipso position of the coordinated arenes. Subsequent Horner–Wadsworth–Emmons (HWE) reaction with added aldehydes affords olefinated spirolactam cyclohexadienyl ruthenium complexes. Mild oxidation with CuCl₂ or CuBr₂ under CO effects removal and recovery of the CpRu(II) fragment. Substituents present on the cyclohexadienyl skeleton influence the outcome of demetalation and products obtained in this study include functionalized 2-azaspiro[4.5]decanes and tetrahydroisoquinolinones.     

Asymmetric synthesis of unsaturated α-benzyloxyaldehydes: an enantioselective synthesis of (+)-exo-brevicomin

Enantioselective synthesis of α-hydroxy aldehydes with an alkene tether was accomplished from l-(+)-tartaric acid, employing stereoselective reduction of a 1,4-diketone with L-selectride as the key step. Synthetic utility of these aldehydes was demonstrated in the synthesis of pine beetle pheromone (+)-exo-brevicomin.     

A new general, practical and enantioselective synthesis of α-amino acids

In recent years, considerable efforts have been expended to the development ofenantioselective synthesis of α-amino acids and the use of α-amino acids as chiralbuilding blocks for the synthesis of complex molecules. Numerous unnatural aminoacids which are often the characteristic units of biologically active peptides, have alsobeen discovered. Herein we describe a convenient and general access to natural andunnatural α-amino acids which are based on the use of the chiral building blocks,(S)-1a-e and (R)-1a-e from kinetic resolution of α-furfuryl amines (Scheme 1).     

Enzyme-Mediated Preparation of (+)- and (–)-cis-α-Irone and (+)- and (–)-trans-α-Irone

The preparation of (−)- and (+)-trans-α-irone ( 1a and 1b , resp.) and of (+)- and (−)-cis-α-irone ( 1c and 1d , resp.) from commercially available Irone alpha ^® is reported. The relevant step in the synthetic sequence is the initial chromatographic separation of crystalline (±)-4,5-epoxy-4,5-dihydro-cis-α-irone ((±)- 5 ) from oily (±)-4,5-epoxy-4,5-dihydro-trans-α-irone ((±)- 4 ). The latter was subsequently converted, after NaBH₄ reduction, into the crystalline 3,5-dinitrobenzoate ester (±)- 8 , thus allowing a complete separation of the two corresponding diastereoisomeric alcohol derivatives. Suitable enantiomerically pure precursors of the desired products 1a – d were obtained by kinetic resolution of the racemic allylic alcohols derived from (±)- 5 and (±)- 8 , mediated by lipase PS (Amano). The last steps consisted of MnO₂ oxidation and removal of the epoxy moiety with Me₃SiCl/NaI in MeCN. External panel olfactory evaluation showed that (−)-cis-α-irone ( 1d ) has the finest and most distinct `orris butter' character.     

Carbohydrate‐2‐deoxy‐2‐phosphonates: Simple Synthesis and Horner–Emmons Reaction

Phosphorus meets carbohydrates : Dimethyl phosphite reacts with ceric(IV) ammonium nitrate (CAN) to give phosphonyl radicals that add to glycals 1 . The derivatives 2 were isolated in high yields and during a subsequent Horner–Emmons reaction underwent an interesting elimination to give 3,6‐dihydro‐2H‐pyrans 3 . The short sequence with simple precursors is applicable to the transformation of hexoses, pentoses, and disaccharides. Bn=benzyl.

     

A concise synthesis of chilenine via a sequential reaction process

A new short synthesis of chilenine has been achieved in two steps. The precursor amide was readily prepared by the condensation of the corresponding amine and acid. Treatment of the amide with oxalyl chloride in the presence of AlCl₃ at room temperature afforded the desired product chilenine through sequential Friedel-Crafts acylation, amide cyclization to imide, and intramolecular Friedel-Crafts type reaction. The synthesis suggests a new potential of oxalyl chloride for a two-carbon synthon.     

Palladium-catalysed synthesis of α-methylene γ-butyrolactams via cyclisation of homoallylic chloroformamides

3-Methylene 2-pyrrolidinones were prepared by intramolecular cyclisation of homoallylic chloroformamides catalysed by Pd^II or Pd° complexes.     

The synthesis of β-heteroarylamino-α,β-dehydro-α-amino acid derivatives via thiazolones

2-Alkoxy-4-heteroarylaminomethylene-5(4H)-thiazolones 4 were converted with various nucleophiles into β-heteroarylamino-α,β-dehydro-α-amino acid derivatives 11, 14, 15, 16, 17, 18 , and 19 . Reduction of 4 with sodium borohydride in ethanol saturated with gaseous ammonia afforded the corresponding β-heteroaryl-amino substituted alanyl amides 20 . Thiazoledione derivative 7a was transformed with sodium methoxide in methanol into 1-(4,6-dimethylpyrimidinyl-2)-4-mercaptocarbonylimidazol-2(3H)-one ( 8a ).     

1,6-Asymmetric induction: A higher enantioselective synthesis of γ-butyrolactone

A novel 1,6-asymmetric induction has been observed in the iodolactonization of γ, delta;-unsaturated amides. The optically active γ-butyrolactone was synthesized by employing iodolactonization reaction as a key step.     

The furan approach to oxacycles. Part 4: A synthesis of (+)-decarestrictine L

We describe an efficient new approach for the enantioselective synthesis of (+)-(2R,3S,6R)-decarestrictine L from commercially available starting material using our newly developed methodology based on the oxidation of a furan ring with singlet oxygen followed by an intramolecular hetero Michael addition.