Permethacrylated carbohydrates: synthesis and reactivity in glycosidation reaction

The synthesis of various permethacrylated mono- and disaccharides in acceptable yields is reported. The reactivity of these unusual polymerizable compounds has been investigated in diverse glycosidation reaction conditions. New original polymerizable donor sugars have been prepared successfully in good to excellent yields.     

First stereoselective synthesis of 2-deoxy-alpha-D-ribosyl-1-phosphate: novel application of crystallization-induced asymmetric transformation

A first stereoselective synthesis of bis(cyclohexylamine) 2-deoxy-alpha-D-ribosyl-1-phosphate has been achieved. The synthesis features a key crystallization-induced asymmetric transformation (AT) to generate a desired alpha-anomer in 99% yield at a 98.8:1.2 ratio of alpha/beta.     

Solvent-free asymmetric aminoalkylation of electron-rich aromatic compounds: stereoselective synthesis of aminoalkylnaphthols by crystallization-induced asymmetric transformation.

Electron-rich aromatic compounds such as 2-naphthol give a faster and asymmetric 1-aminoalkylation with high yields when treated with (R)-1-phenylethylamine and aromatic aldehydes in solvent-free conditions. An asymmetric transformation of a second kind, probably induced by the preferential crystallization of one diastereomer, affords the straightforward and stereoselective synthesis of aminoalkylnaphthols. Mechanisms predictable for this asymmetric reaction are reported. The absolute configurations and the conformations of the unknown aminonaphthols are widely ascertained.     

A highly stereoselective synthesis of chiral alpha-amino-beta-lactams via the Kinugasa reaction employing ynamides

A highly stereoselective synthesis of chiral alpha-amino-beta-lactam through an ynamide-Kinugasa reaction is described. In addition, a mechanistic model is illustrated here to rationalize the observed diastereoselectivity, which depends on both the initial [3 + 2] cycloaddition step and the subsequent protonation for which both are highly selective.     

Promising anticancer drug thapsigargin: A perspective toward the total synthesis

The guaianolide ring containing sesquiterpene thapsigargin is found in the roots and fruits of Mediterranean plant Thapsia garganica L. It is known for its activity as a potent antagonist for Ca²⁺-ATPase (sarco–endoplasmic reticulum Ca²⁺-ATPase) inhibition. Recently, a prodrug mipsagargin is being investigated to target the blood vessel of the cancer cells for the treatment of tumors. The limited natural supply (low isolation and only localized growth (Mediterranean area)) from the natural sources strongly urges for the development of chemical synthetic strategies to access these natural products. This review pertain the various strategies used so far in the thapsigargin’s synthesis, focusing on major contributions in the total synthesis till date.     

Lewis acid-catalyzed stereoselective lactonization and subsequent glycosidation of 2-C-malonyl carbohydrates

Gold(III) bromide is a suitable catalyst for the stereoselective cyclization of 2-C-malonyl carbohydrates to the anomeric center under retention of one ester group. Reopening of the lactones with alcohols in the presence of TMSOTf affords allyl, propargyl and benzyl glycosides with high α-selectivity.     

A stereoselective synthesis of squalamine

Squalamine (1) was synthesized stereoselectively in 14 steps and 19% overall yield from 3-keto-5-chenodeoxycholanate (2) by using a modified Sharpless asymmetric dihydroxylation as the key step.     

A stereoselective synthesis of xylitol

Rel-(2S, 3R, 4R)- (6) and rel-(2R,3R,4R)- (7) 1,2,5-triacetoxy-3,4-epoxypentanes have been obtained in seven steps starting from cyclopentadiene. Both diastereoisomers afford xylitol pentaacetate (8) selectively upon epoxide cleavage with acetate ion. In the case of (6), rel-(1s,3R,4r,5S)-3,-bisacetoxymethyl-1-methyl-2,6,7-trioxabicyclo- [2.2.1]heptane (11) has been isolated and characterised as an intermediate in the reaction.     

A novel promoter, heteropoly acid, mediated chemo- and stereoselective sulfoxide glycosidation reactions

The chemo- and stereoselective glycosidations of sulfinylglycosides and alcohols using a heteropoly acid, H₃PW₁₂O₄₀, as a new promoter have been developed.     

A stereoselective formal total synthesis of (+)-hyperaspine via a tandem aza-Michael reaction

A stereoselective formal total synthesis of (+)-hyperaspine via a tandem aza-Michael reaction as the key step in good yield is reported.     

First total synthesis of salinipyrone A using highly stereoselective vinylogous Mukaiyama aldol reaction

A synthetic approach for the total synthesis of salinipyrone A has been developed. Key steps involve the TiCl₄-mediated vinylogous Mukaiyama aldol reaction (VMAR) of chiral ketene silyl N,O-acetal with propionaldyhyde, an aldol condensation, Witting olefination, and a cyclization. The synthesis proceeds in eight steps.     

Enantioselective synthesis of the oxadecalin core of phomactin A via a highly stereoselective Diels-Alder reaction

Phomactin A (1) is a selective antagonist of platelet activating factor (PAF). Herein, we report our progress toward the construction of the oxadecalin core of 1. This route is based on the Diels-Alder cycloaddition of an appropriately functionalized vinyl pyran and a complementary dienophile. A model of this reaction involving 2 and maleic anhydride was conducted. Adduct 3 contains the correct stereochemical arrangements between functional groups necessary for gaining access to phomactin A. Reaction: see text.     

Intramolecular Nicholas reaction: stereoselective synthesis of 5-alkynylproline derivatives

The intramolecular Nicholas reaction of propargylic alcohols derived from N, N-acyl-diprotected omega-semialdehydes obtained from glutamic acid provided stereoselectively 5-alkynylproline derivatives. The suitable choice of the N-protecting group (tosyl or benzoyl derivative) permitted control of the stereochemistry during the ring formation. Semiempirical calculations of the species involved in the cyclization support the observed stereochemistry.     

A general stereoselective method for the synthesis of cyclopropanecarboxylates. A new version of the homologous Horner-Wadsworth-Emmons reaction

The synthesis of alpha-, beta- and gamma-substituted alpha-phosphono-gamma-lactones was accomplished using different ring closure and ring homologation strategies. It was found that the lactones could be selectively transformed into the corresponding ethyl cyclopropanecarboxylates by treatment with sodium ethoxide in boiling THF. The reported reaction provides an attractive alternative to the classical homologous Horner-Wadsworth-Emmons approach to the construction of cyclopropanes with electron-withdrawing functionalities.     

Asymmetric synthesis of (-)-dihydroxanthatin by the stereoselective Oshima-Utimoto reaction

[reaction: see text]. The catalytic stereoselective Oshima-Utimoto reaction is useful for the construction of five-membered oxacycles from simple starting materials and was employed for the preparation of the lactone group in the asymmetric synthesis of (-)-11alpha,13-dihydroxanthatin. Completion of the synthesis is facilitated by ring-closing enyne metathesis and alkene cross metathesis reactions.     

A facile reaction of imines with telluronium allylide. Highly stereoselective synthesis of vinylaziridines

The reaction of telluronium allylides with alkylimines, generated in situ from alpha-amidoalkyl sulfones, affords cis-alkylvinylarizidines with good stereoselectivity in good yields. However, the same ylides react with N-aryl imines to provide trans-vinylaziridines.     

A stereoselective formal synthesis of leucascandrolide A

A stereoselective formal synthesis of leucascandrolide A was accomplished through the tandem and organocatalytic oxa-Michael reactions, which were promoted by the gem-disubstituent effect, in conjunction with the dithiane coupling reaction.