Cross‐metathesis of C‐Glycosides and Peptides

Peptides bearing an acryloyl residue at their N‐terminus were coupled with various C‐glycosides in an equimolar ratio via cross‐metathesis. The newly formed olefin was obtained with high E/Z selectivity in satisfying to high yields with low homodimerization of the starting materials. The posttranslational cross‐metathesis approach was shown to be suitable for the combinatorial synthesis of a small library of C‐glycopeptides.     

Olefin Cross‐Metathesis: A Powerful Tool for Constructing Vaccines Composed of Multimeric Antigens

The preparation of biologically pertinent glycosylamino acids from O‐pentenyl glycosides is described. The procedure involves sequential cross‐metathesis reactions followed by hydrogenation. The generality and value of this procedure have been demonstrated by the preparation of peracetylated Gb3, GM2, and fucosyl GM1 glycosylamino acids, which are of potentially large value in the preparation of future anticancer vaccines.     

Radical Mediated Diastereoselective Synthesis of Benzothiazole Sulfonyl Ethyl C‐Glycosides

Diastereoselective synthesis of a variety of benzothiazole sulfonyl ethyl C‐glycosides has been developed by a radical mediated approach on the reaction of glycosyl bromides and benzothiazolyl vinyl sulfone in the presence of n‐Bu₃SnH and AIBN in good yields.     

Synthesis of C‐3 Branched Allyl and Pentadienyl Glucosamines via Radical Coupling of Sugar‐Thionocarbonates

Abstract

The intermolecular AIBN‐promoted free radical reaction of glucosamine thionocarbonates as radical donors, and allyl or pentadienyl‐tributyltin reagents gave the expected C‐3 branched sugar derivatives in good yield and with total equatorial selectivity.     

Selective Reductions of C‐(4,6‐O‐Benzylidene‐β‐d‐glucopyranosyl) Nitromethane

Abstract

The nitromethyl group of C‐(4,6‐O‐benzylidene‐β‐d‐glucopyranosyl) nitromethane was manipulated by various reduction and oxidation methods and further functionalizations into –CH₂NHOH, –CH?NOH, –CN, –CH?O, and –CH₂NHCONH₂, all with retention of the 4,6‐O‐benzylidene group. Certain reduction methods gave rise to a novel secondary amine via an unusual dimeric aminal.     

Preparation of 4‐Arylcyclopentenes by Sequential Diallylation of Arylaldehydes and Ring‐Closing Metathesis

Abstract

Allylsilane diallylation of aryl aldehydes followed by ring closure metathesis leads to 4‐arylcyclopentenes in good yields.     

Selective Mono‐BOC Protection of Diamines

A facile route for mono‐BOC protection of symmetrical and unsymmetrical diamines was developed by sequential additions of 1 mol of HCl and 1 mol of (BOC)₂O followed by neutralization.     

Efficient Selective Formation of C‐C Single Bonds and C˭C Double Bonds by NBS‐Promoted Oxidative Coupling of β‐Keto Esters

Abstract

A new application of NBS, which results in the oxidative coupling of β‐keto esters to selectively form C‐C single and C?C double bonds, can be controlled by the amount of NBS and t‐BuOK employed. This methodology adds a new entry to C‐C single and C?C double‐bond formation between active methylene groups under mild conditions with high selectivity.     

Novel Synthesis of Dihydrothiazoles from the Selenium‐Induced Cyclization of Allyl Thioureas

The reaction of allylic thioureas with phenylselenenyl chloride affords 2‐amino dihydrothiazoles in excellent yields by selenium‐induced cyclization of allylic thioureas.     

Effect of Substitution in Stannic Chloride–Mediated Heterocyclization of 4‐Allyl‐3‐hydroxyquinolin‐2(1H)‐ones

Effect of substituents at the allylic position in a stannic chloride–iodine–mediated heterocyclization of 4‐allyl‐3‐hydroxyquinolin‐2(1H)‐ones for the regioselective formation of five‐ and six‐membered heterocyclic rings has been rationalized by the application of restricted Hatree–Fock calculation.     

Microwave‐Enhanced Ferrier Reaction: A Facile Synthesis of 2,3‐Unsaturated‐O‐Glycosides Under Solvent‐Free Conditions

A variety of 2,3‐unsaturated‐O‐glycosides have been prepared by the Ferrier rearrangement of acetyl protected glycals under microwave irradiation using silica gel as an acid catalyst. Environmental friendliness, high yields, and short reaction times are the key features of this method. Furthermore, the method was applicable not only to the Ferrier reaction of 3,4,6‐tri‐O‐acetyl glucal and 3,4,6‐tri‐O‐acetyl galactal but also to the Ferrier reaction of 3,4‐di‐O‐acetyl arabinal.     

Metathesis reactions of Δ-steroids

Metathesis reactions of Δ²²-steroids are studied. The cross metathesis reactions of model Δ²²-steroids with excess of simple alkenes are sluggish or do not occur at all. In contrast, derivatives of both trans- and cis-Δ²²-cholesterol undergo ring closing metathesis reactions but the former reacts faster. However, the side chain double bond in stigmasterol and ergosterol is too crowded for metathesis reactions promoted by currently available catalysts.     

Convenient Synthesis of Tolcapone,a Selective Catechol‐O‐methyltransferase Inhibitor

A convenient and efficient synthesis of tolcapone from commercial 4‐benzyloxy‐3‐methoxybenzaldehyde is presented. Grignard reaction of 4‐benzyloxy‐3‐methoxybenzaldehyde (1) with p‐tolylmagnesium bromide followed by Oppenauer oxidation of the hydroxyl functionality and subsequent O‐debenzylation gave phenol 5. Compound 5 was regioselectively nitrated and then subjected to O‐demethylation to produce tolcapone in 60% overall yield.     

Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

Synthesis of 3,4,5‐Tris(alkyloxy)benzyl Glycosides as Glycolipid Analogues

Abstract

A series of 3,4,5‐tris(alkyloxy)benzyl glycosides of D‐glucose, D‐galactose, D‐mannose, N‐acetyl‐D‐glucosamine and N‐acetyl‐D‐galactosamine were prepared by the trichloroacetimidate procedure. After immobilization on a hydrophobic surface, the affinity of the carbohydrate to a lectin was evaluated using a surface plasmon resonance biosensor. The selective interaction achieved with the lectin showed that the glycosides had potential for use as glycolipid analogues. The 3,4,5‐tris(dodecyloxy)benzyl glycosides were soluble in ethanol, and potentially would be useful for cell culture experiments.     

Acid‐Catalysed Selective Monoiodination of Electron‐Rich Arenes by Alkali Metal Iodides

Abstract

The reaction of electron‐rich arenes with alkali metal iodides such as sodium and potassium iodides in the presence of conc. H₂SO₄ gives p‐iodoarenes in high yields.     

Synthesis and Characterization of a New UV Cross‐linkable Waterborne Siloxane‐polyurethane Dispersion

A new cross‐linkable waterborne siloxane‐polyurethane dispersion (PEDA‐SiPU) was synthesized by incorporating the acrylate groups into the side chain of the polyurethane using the pentaerythritol diacrylate(PEDA) and introducing polysiloxane groups into the soft segment of the polyurethane using dihydroxybutyl‐terminated polydimethylsiloxane (PDMS). They can form the cross‐linking structure by UV radiation in the presence of a photo‐initiator. Fourier transform infrared spectroscopy (FTIR) was used to identify the chain structure of PEDA‐SiPU. The effect of the PDMS content and the PEDA content on the C?C conversion behaviors under UV irradiation was investigated. Water resistance and the mechanical properties of the UV cured films were also studied. Through the controlling of suitable content of PDMS and PEDA introduced in the chain, the obtained PEDA‐SiPU films were proved to possess both good water resistance and mechanical properties.     

Ferric Sulphate Hydrate–Catalyzed,Microwave‐Assisted Synthesis of 2,3‐Unsaturated O‐Glycosides via the Ferrier Reaction

Fe₂(SO₄)₃ · xH₂O catalyzes the Ferrier reaction of per‐O‐acetylated/benzylated glycals with alcohols to give 2,3‐unsaturated α‐glycosides in a few minutes under microwave irradiation.     

Highly Regio‐ and Stereoselective Synthesis of β‐Phenyl‐chalcogenyl Allyl Sulfones by Hydrochalcogenation Reaction of 1,2‐Allenyl Sulfones

The hydrochalcogenation of allenyl sulfones with sodium organyl chalcogenolates can proceed smoothly to give β‐phenylchalcogenyl allyl sulfones in high yields with exclusive regioselectivity. For the asymmetric allenyl sulfone, the reaction has both high regio‐ and stereoselectivity with the predominace of E‐isomer. Some applications of β‐phenyltelluro and β‐phenylselanyl allyl sulfone in organic synthesis are also investigated.