Synthesis of 3,6‐Branched β‐d‐Glucose Oligosaccharides

A glucohexasaccharide, β‐d‐Glcp‐(1 → 3)‐[β‐d‐Glcp‐(1 → 3)‐β‐d‐Glcp‐(1 → 6)]‐β‐d‐Glcp‐(1 → 3)‐β‐d‐Glcp‐(1 → 3)‐β‐d‐Glcp was synthesized as its 4‐methoxyphenyl glycoside via 2 + 2 + 2 strategy with benzylidenated glucose mono‐ and disaccharides as the key intermediates.     

Facile and Efficient Synthesis of Substituted 1,4‐Dithiafulvalenes from β‐Dicarbonyl Compounds

A facile and efficient synthetic route to substituted 1,4‐dithiafulvalenes has been developed. The precursors 2 may be easily prepared from the reactions of β‐dicarbonyl compounds 1 with CS₂ and 1,2,3‐tribromopropane under mild conditions. The elimination of HBr of 2 in basic media furnishes corresponding acetyl substituted 1,4‐dithiafulvalenes 3 in 85–93% yields. The aldol condensation reaction of 2 with various arylaldehydes affords alkenoyl substituted 1,4‐dithiofulvalenes 4 in high to excellent yields.     

Crystal Structures of β‐1‐N‐Chloroacetamido Derivatives of d‐Glucose and d‐Galactose

Crystal structures of 1‐N‐(β‐d‐glucopyranosyl)chloroacetamide (1), an inhibitor of glycogen phosphorylase, and the corresponding galactopyranosyl amide (2) have been determined. Both crystals belong to P2₁2₁2₁ space group with 1 having the unit cell dimensions of a = 7.939(3), b = 9.547(3) and c = 14.157(2) Å, while those of 2 are, a = 7.636(10), b = 9.004(8) and c = 14.807(5) Å. The sugar ring takes a ⁴ C ₁ conformation and the amide linkage exists in Z‐anti conformation in both crystals. The torsion angle O5–C1–N1–C1′ is ? 93.9(5) for 1 and ? 111.5(3)° for 2. The conformational preference of Cl and N1 in 1 and 2 is found to be between anti and gauche. The molecular assembly in both 1 and 2 is stabilized by a finite chain of hydrogen bonds starting from N1H and ending at O1′, whereas a ten membered hydrogen‐bonded ring involving O4H and O5 is observed in 1.     

N‐Methylation of Nitrogen‐Containing Heterocycles with Dimethyl Carbonate

Reactivity of dimethyl carbonate, the environmentally friendly reagent, as methylating agent for nitrogen‐containing heterocyclic compounds has been studied. Reactions of imidazole, pyrazole, pyrrole, morpholine, and piperazine with dimethyl carbonate to afford N‐methylated products were reported. The reactions were carried out with neither catalyst nor solvent at a temperature range of 110–170°C under atmospheric pressure.     

Preparation of Nitrogen Heterocycles of Spiro[Furo[2,3‐d]‐Pyrimidine]Pyrimidine Derivatives

Abstract

The NMR evaluation of the reaction progression of the bromination of heterocyclic dibarbiturates was used to develop an efficient synthetic procedure for the preparation of heterocyclic spiro[furo]pyrimidines. The structure of one of these compounds was confirmed by X‐ray analysis.     

Efficient Synthesis of N‐Cyano α and β‐Amino Esters

A versatile method for the synthesis of N‐cyano α and β‐amino esters is described. Reaction of different amino esters with cyanogen bromide in dry ether gave the corresponding N‐cyano α and β‐amino esters in excellent yields.     

Synthesis of the C‐Glycoside of Methyl α‐d‐Altropyranosyl‐(1→4)‐α‐d‐glucopyranoside

The C‐glycoside of methyl α‐d‐altropyranosyl‐(1→4)‐α‐d‐glucopyranoside 2 was prepared in a convergent fashion, from readily available precursors, 4‐O‐tert‐butyldiphenylsilyl‐1,2‐O‐isopropylidene‐d‐erythro‐S‐phenyl monothiohemiacetal 13 (five steps from D‐ribose) and the known acid, methyl 2,3,6‐tri‐O‐benzyl‐4‐C‐(carboxymethyl)‐4‐deoxy‐α‐d‐glucopyranoside 17 (seven steps from methyl α‐d‐glucopyranoside). The key reactions in the synthesis are the oxocarbenium ion cyclization of thioacetal‐enol ether 19 to a C1 substituted glycal 20, and the stereoselective hydroboration of 20 to the α‐C‐altroside 21.     

New Straightforward Synthesis of β‐Damascenone and β‐Damascone Derivatives from β‐Ionone via Retro‐α‐ionol

β‐Damascenone and β‐damascone derivatives, important fragrant compounds, were directly obtained from β‐ionone by a new way via retro‐α‐ionol.     

Synthesis of Heteroanellated Pyranosides Starting from Methyl 4,6‐O‐benzylidene‐2,3‐dideoxy‐α‐d‐erythro‐hexopyranosid‐2‐ylidenemalononitrile

The hexopyranosid‐2‐ylidenemalononitrile 1 reacted with phenyl isothiocyanate in the presence of triethylamine to furnish (2R,4aR,6S,10bS)‐8‐amino‐4a,6,10,10b‐tetrahydro‐6‐methoxy‐2‐phenyl‐10‐phenylimino‐4H‐thiopyrano[3′,4′:4,5]pyrano[3,2‐d][1,3]dioxine‐7‐carbonitrile (2). Starting from 1, cyclization with sulphur and diethylamine yielded (2R,4aR,6S,9bR)‐8‐amino‐4,4a,6,9b‐tetrahydro‐6‐methoxy‐2‐phenylthieno[2′,3′:4,5]pyrano[3,2‐d][1,3]dioxine‐7‐carbonitrile (3), which could be transformed into the corresponding aminomethylenamino derivative 4 by treatment with triethyl orthoformate and ammonia. Intramolecular cyclization of 4 to yield (2R,4aR,6S,11bR)‐4,4a,6,11b‐tetrahydro‐6‐methoxy‐2‐phenyl[1,3]dioxino[4″,5″:5′,6′]pyrano[3′,4′:4,5]thieno [2,3‐d]pyrimidin‐7‐amine (5) was achieved by using NaH as base. (2R,4aR,6S,9bS)‐8‐Amino‐4a,6,9,9b‐tetrahydro‐6‐methoxy‐9‐(4‐methylphenyl‐sulfonyl)‐2‐phenyl‐4H‐[1,3]dioxino[4′,5′:5,6]pyrano[4,3‐b]pyrrole‐7‐carbonitrile (6) was prepared by treatment of compound 1 with tosylazide and triethylamine.     

KF/Al2O3‐Mediated N‐Alkylation of Amines and Nitrogen Heterocycles and S‐Alkylation of Thiols

KF/Al₂O₃ efficiently catalyzes N‐alkylation of heterocyclic, primary, and secondary amines and S‐alkylation of thiols with a variety of alkyl halides. The N‐alkylation and S‐alkylation adducts were produced in good to excellent yields and in short times.     

Facile Synthesis of Isoquinolines, β‐Carbolines,and 3‐Deazapurines

Isoquinoline, β‐carbolines, and 3‐deazapurines were prepared in 52–81% yields via oxidative decarboxylation of cyclic α‐amino acids using ammonium persulfate as an oxidant in the presence of catalytic silver.     

Simple and Convenient Synthesis of 21‐Thioalkylether Derivatives of Methyl 16‐Prednisolone Carboxylates

The antedrug approach for corticosteroids has been described as a fundamentally sound approach for the development of safer anti‐inflammatory and anti‐asthmatic therapy. However, the derivatization of prednisolone and its congeners have been considered to be major pitfalls, because their syntheses are complicated by the presence of numerous carboxylate esters and hydroxyl functions in the steroid nucleus. A simple and direct synthesis of 21‐thioalkylether derivatives of methyl 16‐prednisolonecarboxylates is described. The 21‐mesylate of the methyl 16‐prednisolonecarboxylate and 9‐fluoro‐17‐dehydro methyl 16‐prednisolonecarboxylate were reacted with Na‐thioalkoxides to furnish the desired thioethers in good yields. A previously published method for the methanolysis of 16‐cyanoprednisolone to methylcarboxylate has been reexamined, and the conditions are explained clearly. The reaction conditions for all these reactions were critical.     

Convenient Procedure for Synthesis of N‐Protected β‐Aminomalonates and β‐Amino Acids From α‐Amidosulfones

A synthesis of N‐protected β‐aminomalonates starting from α‐amidosulfones under very mild and simple reaction conditions is described. Treatment of the sulfones with malonate esters in the presence of 2.5 equivalents of potassium carbonate affords the desired products in good yield. A variety of N‐Z and N‐Boc protected aliphatic and aromatic α‐aminosulfones and malonate esters have been successfully used as starting materials. Hydrolysis with concomitant decarboxylation of the N‐protected β‐aminomalonates provides a convenient access to racemic β‐amino acids.     

Synthesis of 2,3‐Disubstituted 4‐Pyridone From a β‐Aminocarboxylate Derivative and Acetoacetate

The reaction of diethyl aminomethylenemalonate with ethyl acetoacetate proceeded, when catalyzed by anhydrous hydrogen chloride, toward a respectively substituted α‐ instead of γ‐pyridone derivative formation, contrary to the literature report. Additionally, it was found that the amine used as a starting component in this reaction showed a great tendency to autocondensation under the influence of anhydrous hydrogen chloride to yield 5‐ethoxycarbonyl‐2‐pyridone. The most convenient method to prepare 4‐pyridone 2,3‐disubstituted derivative appeared to be a three‐step synthesis, starting from a chain enamine formation, which was subjected to cyclization, followed by oxidation of the last intermediate. The usefulness of the stepwise synthesis was demonstrated on the 3‐ethoxycarbonyl‐2‐methyl‐4‐pyridone preparation as an example.     

Isolation and Structure Characterization of a (4‐O‐Methyl‐d‐glucurono)‐d‐xylan from the Skin of Opuntia ficus‐indica Prickly Pear Fruits

A slightly water soluble (4‐O‐methyl‐d‐glucurono)‐d‐xylan was isolated from the skin of Opuntia ficus‐indica (OFI) fruits by alkaline extraction, followed by ethanol precipitation and ion‐exchange chromatography. The structure of this xylan was determined by sugar determination coupled with a ¹H and ¹³C NMR spectroscopy analysis. The xylan consisted of a linear (1→4)‐β‐d‐xylopyranosyl backbone decorated with 4‐O‐methyl‐α‐d‐glucopyranosyluronic acid groups linked to the C‐2 of the xylopyranosyl residues, in the ratio of one uronic acid for six neutral sugar units.     

Efficient Synthesis of Phosphono‐ and Phosphinoxidomethylated N‐Heterocycles under Solvent‐Free Microwave Conditions

Simple N‐heterocycles were converted to N‐phosphono‐ and phosphinoxidomethyl derivatives by a solvent‐free microwave‐assisted condensation of the heterocycle, paraformaldehyde, and diethylphosphite or diphenylphosphine oxide in a convenient and, in most cases, efficient way. In contrast to an earlier report, imidazole proved to be unreactive in this type of phospha‐Mannich reaction.     

Expeditious Synthesis of New 3,4,6‐Trihydroxythiepanes from d‐(‐)‐Quinic Acid

We report herein that the new seven‐membered‐ring thiosugars (thiepanes) have been synthesized from d‐(‐)‐quinic acid. The key feature of the synthesis involves the thiocyclization of protected hexane‐1,2,3,5,6‐pentanol derivatives. The subsequent step of acidic removal of protecting groups is critical in the reaction conditions to obtain the required 3,4,6‐trihydroxythiepanes. During the course of studies, the unexpected trihydroxythiopyrans are formed because of the ring contractions of their corresponding trihydroxythiepanes under various conditions.     

Cation‐Exchange Resins: Efficient Heterogeneous Catalysts for Facile Synthesis of Dibenzoxanthene from β‐Naphthol and Aldehydes

β‐Naphthol reacts with alkyl and aryl aldehydes in the presence of Indion‐130 to give 14‐alkyl/aryl‐14H[a,j]dibenzoxanthenes in good yield.     

Improved Preparation of β‐d‐ManNAc‐(1→4)‐d‐Glc and β‐d‐TalNAc‐(1→4)‐d‐Glc Disaccharides and Evaluation of Their Activating Properties on the Natural Killer Cells NKR‐P1 and CD69 Receptors

This article has been retracted.     

CuI/Proline-catalyzed N-Arylation of Nitrogen Heterocycles

Qing Xiang GUON-Arylated heterocycles such as pyrroles, indoles, and imidazoles are important building blocks for the synthesis of natural products, pharmaceuticals, and function materials1. Usually these compounds were synthesized by Cu-catalyzed Ullmann…