Convenient and Regioselective One‐Pot Solvent‐Free Synthesis of ß‐Hydroxyphosphonates

A simple, efficient, regioselective, and solvent‐free method has been developed for the synthesis of β‐hydroxyphosphonates from epoxides and triethyl phosphite using ZnCl₂ in high yields under mild conditions.     

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.     

Crystal Structure and Solid‐State 13C NMR of Methyl α‐d‐Mannofuranoside

The crystal structure of methyl α‐d‐mannofuranoside was determined by X‐ray crystallography. The C‐1–C‐2, C‐2–C‐3, C‐3–C‐4, C‐4–O and O‐4–C‐1 distances within the furanoside ring are 1.513(2), 1.523(2), 1.516(2), 1.445(2) and 1.422(2) Å, respectively. The hydrogen bonding consists of O–H–O interactions which include the anomeric oxygen but exclude the ring oxygen atom. The two hydroxyls OH‐6 and OH‐2 are H‐bond acceptors and donors with H···O distances of 1.92–1.93 Å, whereas the OH‐3 and OH‐5 are only H‐bond donor [H···O distance of 2.04(2) Å]. Additionally, OH‐6 participates in a weak hydrogen bond to the anomeric oxygen [H···O distance of 2.19(3) Å]. The crystalline methyl α‐d‐mannofuranoside adopts an ³ E ring conformation. The analysis of ¹³C CPMAS NMR chemical shifts for solid methyl α‐d‐mannofuranoside confirm such H‐bonding pattern.     

Regioselective Alkylation of Thiazolylsulfonamides: Direct and Efficient Synthesis of 3‐Alkylthiazolidene Derivatives

Various N‐3‐alkylated thiazolidenesulfonamide derivatives were efficiently prepared by the direct endo‐selective alkylation of thiazolylsulfonamides. The effects of different bases and solvents were investigated, and the NaH–THF combination was found to be the most effective at conferring high yields and endo‐selectivity.     

Convenient Method for Synthesis of Substituted 2‐Amino‐2‐chromenes

Some substituted 2‐amino‐2‐chromenes were synthesized by the reaction of arylidenemalononitriles with 1‐naphthol or 2‐naphthol in the presence of sodium hydroxide as catalyst under solvent‐free condition.     

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 Methyl α-d-Allopyranoside and Methyl α-d-Ribo-hexopyranoside: A Convenient Chemoenzymatic Approach

Abstract

An efficient chemoenzymatic synthesis of methyl α-d-allopyranoside and methyl 3-deoxy-α-d-ribo-hexopyranoside starting from methyl 4,6-O-benzylidene-α-d-glucopyranoside is described.     

Convenient,Cost‐Effective,and Mild Method for the N‐Acetylation of Anilines and Secondary Amines

Abstract

An efficient, cost‐effective, and mild method for the N‐acetylation of anilines and secondary amines with ammonium acetate in acetic acid media at reflux temperature in good yield is described.     

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.     

Efficient and Convenient Method for the Synthesis of N‐Arylhydrazones using a Palladium‐Catalyzed Bond‐Forming Reaction

A highly effective, convenient, and reproducible industrial process for palladium‐catalyzed carbon–nitrogen cross coupling has been developed and applied on a large scale. Thus various functionalized N‐arylhydrazones have been easily prepared and well characterized by conventional spectroscopic methods.     

Liquid‐Phase Synthesis of Methyl (E)‐2‐Nitromethyl‐2‐alkenoates Based on PEG‐Supported α‐Phenylselenopropionate

The reaction of the lithio derivative of novel polyethylene glycol (PEG)‐supported α‐phenylselenopropionate with aldehydes, followed by oxidation–elimination with 30% hydrogen peroxide and then treatment with sodium nitrite, formed PEG‐bound 2‐nitromethyl‐2‐alkenoates. Subsequent cleavage from the PEG efficiently afforded methyl (E)‐2‐nitromethyl‐2‐alkenoates in good yields and high purities.     

Regioselective Monoacetylation of Methyl Pyranosides of Pentoses and 6‐Deoxyhexoses by Acetic Anhydride in the Presence of MoCl5

Convenient regioselective syntheses of 3‐acetates of methyl pyranosides of α‐L‐rhamnose, α‐ and β‐L‐arabinose, α‐D‐fucose, α‐D‐lyxose, and β‐D‐ribose with good yields have been attained using MoCl₅ as catalyst. Methyl β‐L‐rhamnopyranoside under this conditions gave 2‐acetate.     

A Novel,Convenient Synthesis of the 3‐O‐β‐D‐ and 4′‐O‐β‐D‐Glucopyranosides of trans‐Resveratrol

Abstract

trans‐Resveratrol‐3‐O‐β‐D‐glucupyranoside (trans‐piceid, 2) and trans‐resveratrol‐4′‐O‐β‐D‐glucupyranoside (trans‐resveratroloside 3) are the naturally occurring O‐glucoside conjugates of the polyphenolic stilbenoid trans‐resveratrol 1. Recently, attention has been drawn towards the interesting biological properties of the glucoside conjugates 2 and 3 as well as those of the aglycone 1. The fact that only limited quantities can be obtained by extraction from natural sources has prompted the development of novel syntheses of 2 and 3, based on a convergent Heck‐coupling strategy, which now conveniently allows for the preparation of multi‐milligram to gram quantities of each.     

Synthesis of Acylated Methyl 2‐Acetamido‐2‐Deoxy‐α‐D‐Mannopyranosides

Abstract

2‐Acetamido‐2‐deoxy‐β‐D‐mannopyranose (1) was glycosylated by the Fischer method using an acidic ion‐exchange resin as the catalyst to give α‐methyl glycoside 2. Selective pivaloylations of methyl 2‐acetamido‐2‐deoxy‐α‐D‐mannopyranoside (2) have been studied under various reaction conditions. Two partially pivaloylated products were submitted to additional acetylations. All structures were established by NMR spectroscopy. Structure of the methyl 2‐acetamido‐2‐deoxy‐3,6‐di‐O‐pivaloyl‐α‐D‐mannopyranoside (4) was determined by X‐ray analysis.     

A Convenient and Efficient Preparation of 2‐Acetyl‐4,5‐difluorothiophene

A convenient, five‐step preparation of 2‐acetyl‐4,5‐difluorothiophene from 2,3‐dibromothiophene is described.     

Convenient and Efficient Method for the Obtainment of Ketones from Highly Hindered Aromatic N,N‐Dimethyl‐amides

A simple and efficient procedure to synthesize highly hindered alkyl aryl ketones that involves the coupling of N,N‐dimethyl‐3,5‐di‐tert‐butylsalicylamide with organolithium compounds is described. Mild reaction conditions and good to excellent yields of the products are the noteworthy advantages of the procedure.     

Conformational Study of α‐N‐Acetyl‐D‐Neuraminic Acid by Density Functional Theory

The stable structures of α‐N‐acetyl‐D‐neuraminic acid (Neu5Acα) in the gas phase were studied at the B3LYP level of theory using 6‐31G(d,p) and 6‐31++G(d,p) basis sets. They are classified into five types according to the patterns of the intramolecular hydrogen bond formations. One of the stable structures had intramolecular hydrogen bond network of O₉H_O9 … O₈H_O8 … O?C₁‐O₁H_O1 and O₇H_O7…O?CHN‐C₅ similar to the crystal structure of Neu5Ac‐α‐methyl glycoside methyl ester. The stable structures of Neu5Acα are reasonable for the following sialooligosaccharide ligand studies with respect to the relationship between OH group orientations and intramolecular hydrogen bond formations. The barrier heights for isomerizations between the stable structures were computed to be 2.8 to 6.7 kcal/mol at the B3LYP/6‐31++G(d,p)//B3LYP/6‐31G(d,p) level, which are basic factors for the conformational behavior of Neu5Acα before its interactions with receptors. We also calculated Neu5Acα–4 or 5‐water complexes to take account of the solvent effect on the intramolecular hydrogen bonds in the stable structures. Consequently, the structures of Neu5Acα in the complexes are similar to each other, which is consistent with the known NMR data. Thus, the optimum Neu5Acα‐water complexes are some of the reasonable pseudohydrous Neu5Acα.     

Synthesis of an α‐Gal epitope α‐D‐Galp‐(1→3)‐β‐D‐Galp‐(1→4)‐β‐D‐Glcp NAc–lipid conjugate*

The synthesis of a neoglycoconjugate containing the Galili epitope trisaccharide connected to a spacer‐lipid entity is described. The α‐D‐Galp‐(1→3)‐β‐D‐Galp‐(1→4)‐β‐D‐GlcpNAc trisaccharide, equipped with a 3‐aminopropyl spacer, is efficiently assembled from easily accessible building blocks in a one‐pot procedure. Global deprotection of the trisaccharide and ensuing introduction of a bis(palmitamido)‐ propanamido moiety afforded title compound 1 as depicted in Scheme 1.     

A Convenient Method of Synthesis of Ferrocenylethynyl Ketones

It is well known that molecules possessing extensive conjugated π-electron systems exhibit large non-linear optical properties,[1,2] but the compounds of ferrocenylethynyl ketones have not been reported so far. We now reported preparation of some ferrocenylethyl ketones. These new ethynylketones containing ferrocenyl were prepared conveniently via coupling reaction catalyzed by PdCl2(PPh3)2/PdBzCl(PPh3)2-CuI from ferrocenylethyne and acyl chlorides. This coupling reaction proceeded smoothly in argon and free-water atmosphere at room temperature and gave coupling products in satisfactory yields. All products were characterized by 1H NMR, MS, IR and UV spectra.