Nucleophilic displacement by azide and cyanide on Baylis-Hillman acetates in water

Baylis-Hillman acetates undergo smooth nucleophilic displacement with sodium azide and sodium cyanide in water under mild conditions to afford the corresponding ethyl 2-azidomethyl-3-phenylpropenoate, 2-azidomethyl-3-phenylacrylonitrile and 2-(phenylmethylidene)succinonitrile in excellent yields.     

Reactive polymeric nanoparticles based on unconventional dextran derivatives

Unconventional dextran derivatives with reactive tosyl- and deoxy-azido moieties were synthesized homogeneously under various reaction conditions. Well soluble tosyl dextran of a high degree of substitution up to 1.66 was prepared applying N,N-dimethylacetamide/LiCl as solvent. Almost 50% of secondary toslyate moieties could be replaced by nucleophilic displacement reaction with azide ions. The structure of the products was efficiently analyzed by NMR spectroscopy also after peracylation of the unconventional dextran derivatives. Applying a simple dialysis technique, nanospheres with a size in the range from 160 to 420 nm (D50%) were obtained that possess reactive functional tosyl- and deoxy-azido groups.     

Preparation of 5-Alkylthio and 5-Arylthiotetrazoles from Thiocyanates Using Phase Transfer Catalysis

A very efficient method of preparation for 5-alkyl and 5-arylthiotetrazoles from the corresponding alkyl or aryl halides is described. The halides are first transformed into thiocyanates which further react with azide, yielding the corresponding tetrazoles with [2+3] polar cycloaddition. All synthetic transformations are performed under phase transfer catalytic conditions. The yields vary from good to excellent except for the preparation of 5-benzylthiotetrazole, where the reaction between benzyl thiocyanate and azide [2+3] cycloaddition is in competition with nucleophilic substitution, with benzyl azide as product.     

Catalyst-free aromatic nucleophilic substitution of meso-bromoporphyrins with azide anion: efficient synthesis and structural analyses of meso-azidoporphyrins

meso-Mono- or diazidoporphyrins were readily obtained in high yields by the catalyst-free aromatic nucleophilic reaction of the corresponding bromoporphyrins with azide anions under mild conditions. The molecular structures of the obtained azides were unambiguously determined by X-ray crystallographic analysis.     

Protection des phenols par le groupement azidomethylene application a la synthese de phenols instables

Phenols are protected by the azidomethylene group in basic, nucleophilic, oxidative, weakly reductive and weakly acidic media. This group is obtained by the reaction of sodium azide with aryloxymethyl chlorides. Its utility lies in the ease with which it can be removed under very mild conditions which allows the synthesis of very unstable phenolic compounds.     

Synthesis of New Substituted 4-Amino-3,5-dinitropyridine Derivatives

Facile synthetic routes for the preparation of some new 4-amino-3,5-dinitropyridine derivatives have been revealed. Nitration of 2-chloropyridin-4-amine （1） as a starting material, in an unexpected one-step reaction, to give dinitrated derivatives, followed by nucleophilic substitution reactions with sodium azide, potassium fluoride, ammonia, methylamine, and 4-nitroimidazol, respectively, gave substituted 4-amino-3,5-dinitropyridine derivatives. Meanwhile, its azide derivative underwent a ring closure conversion into 7-amino-6-nitro-[1,2,5]oxadiazolo[3,4-b]- pyridine-1-oxide. It is of significance that all of the nucleophilic substitution reactions were carried out under mild conditions.     

Ionic liquid as an efficient promoting medium for two-phase nucleophilic displacement reactions

The use of the room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate as an efficient catalyst and solvent for several representative nucleophilic substitution reactions under aqueous-RTIL phase transfer conditions was explored. Recycling and reuse of the reaction medium was demonstrated for the azide formation.     

Azide functional monolayers grafted to a germanium surface: model substrates for ATR-IR studies of interfacial click reactions

High-quality azide-functional substrates are prepared by a low temperature reaction of 11-bromoundecyltrichlorosilane with UV-ozone-treated germanium ATR-IR plates followed by nucleophilic substitution of the terminal bromine by addition of sodium azide. The resulting monolayer films are characterized by atomic force microscopy (AFM), contact angle analysis, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR-IR), and ellipsometry. XPS and ellipsometric thickness data correspond well to the results of molecular model calculations confirming the formation of a densely packed azide-functional monolayer. These azide-functional substrates enable interfacial "click" reactions with complementary alkyne-functional molecules to be studied in situ by ATR-IR. To illustrate their potential utility for kinetic studies we show that, in the presence of copper(I) catalyst, the azide-modified surfaces react rapidly and quantitatively with 5-chloro-pentyne to form triazoles via a 1,3-dipolar cycloaddition reaction. Time-resolved ATR-IR measurements indicate that the interfacial click reaction is initially first order in azide concentration as expected from the reaction mechanism, with a rate constant of 0.034 min(-1), and then transitions to apparent second order dependence, with a rate constant of 0.017 min(-1)/(chains/nm(2)), when the surface azide and triazole concentrations become similar, as predicted by Oyama et al. The reaction achieves an ultimate conversion of 50% consistent with the limit expected due to steric hindrance of the 5-chloro-pentyne reactant at the surface.     

Convenient synthesis of sulfonyl azides using PEG-400 as an efficient and eco-friendly reaction medium

Sulfonyl azides have efficiently been synthesized via a convenient and environmentally benign procedure, in which sulfonyl chlorides undergo nucleophilic substitution reaction with sodium azide in PEG-400 under mild conditions. The sulfonyl azides were obtained in 84–97% isolated yields.

     

Synthesis of a conformationally locked version of puromycin amino nucleoside

[reaction: see text] A conformationally locked carbocyclic version of puromycin amino nucleoside was synthesized via Mitsunobu coupling of a 3-azido-substituted carbocyclic moiety with 6-chloropurine without interference from the azido group reacting with triphenylphosphine. The requisite 3-azido-substituted carbocyclic pseudosugar was prepared by a double inversion of configuration at C3' (nucleoside numbering) involving a nucleophilic displacement with azide.     

Reactions of acyl azides with secondary amines in the presence of copper(ii) acetate

The nucleophilic substitution of the azide group in acyl azides for secondary amines in the presence of copper(ii) acetate was studied. The formation of the corresponding amides and copper(ii) azide in the course of the reaction was observed. The shift of the absorption band of stretching vibrations of the azide group was observed in the IR spectra of the reaction products, which could be explained by the intermediate formation of a complex of acyl azide with the amine complex of copper(ii) acetate and by its decomposition to form copper(ii) azide and the corresponding amide. A blue-green color of the solution characteristic of copper(ii) acetate changed in the course of the reaction to the brown color of a solution of copper(ii) azide.     

The synthesis and reactions of certain pyridazine 1-oxides

Nucleophilic displacement reactions under acidic and basic conditions have been studied with 4,6-dinitro-3-methoxypyridazine 1-oxide ( 1 ) and with 6-chloro-3-methoxy-4-nitropyridazine 1-oxide ( 2 ). Depending on the nature of the nucleophilic reagent and the conditions of the reaction we have found that the chloro group, the nitro group, as well as the methoxy group of 1 and 2 may be displaced by the nucleophile. This type of compound possesses significant in vitro antifungal activity.     

Orthoacylimines: a new class of chiral auxiliaries for nucleophilic addition of organolithium reagents to imines

A new class of orthoacylimine-derived chiral auxiliaries has been synthesized and tested in the nucleophilic addition of organolithium reagents to imines. The precursors can be prepared by an aza-Wittig reaction between the corresponding orthoacyl azide and a variety of aldehydes in the presence of trialkylphosphines. The nucleophilic addition of organolithium reagents led to the addition products in good yields and with good to excellent diastereoselectivities (from 85:15 to 99:1). The chiral, nonracemic secondary amines could be readily obtained under mild hydrolytic condition. Furthermore, the chiral auxiliary can be recovered in quantitative yield and reconverted to the starting orthoacyl azide precursor. This method was applied to the synthesis of (S)-t-leucine.     

A Study of Graphene‐Based Copper Catalysts: Copper(I) Nanoplatelets for Batch and Continuous‐Flow Applications

The use of graphene derivatives as supports improves the properties of heterogeneous catalysts, with graphene oxide (GO) being the most frequently employed. To explore greener possibilities as well as to get some insights into the role of the different graphenic supports (GO, rGO, carbon black, and graphite nanoplatelets), we prepared, under the same standard conditions, a variety of heterogeneous Cu catalysts and systematically evaluated their composition and catalytic activity in azide–alkyne cycloadditions as a model reaction. The use of sustainable graphite nanoplatelets (GNPs) afforded a stable Cu^I catalyst with good recyclability properties, which are compatible with flow conditions, and able to catalyze other reactions such as the regio‐ and stereoselective sulfonylation of alkynes (addition reaction) and the Meerwein arylation (single electron transfer process).     

Photolysis of zinc azide in the solid state

The photolysis of anhydrous zinc azide prepared by (1) dehydration of Zn(N₃)₂·2H₂O and (2) precipitation by acetone from aqueous solution, under the action of high pressure mercury arc is reported here. The pressure of nitrogen developed during photolysis under steady-state conditions at constant intensity is a linear function of t^1/2 in both the samples. The rate of photolysis is a linear function of intensity at constant temperature. A detailed analysis of the dark rate suggests that the dependence on t^1/2 should be due to the diffusion of nitrogen from the reaction site to the surface of the solid azide. An appropriate mathematical analysis is presented. The linear dependence of the rate of photolysis on the intensity of irradiation is interpreted in terms of the reaction of a trapped exciton with an adjacent azide ion. Absence of any detectable photoconduction in the wavelength range of the irradiating radiation suggests that excitons are the most probable reactive species. The sample of zinc azide obtained by the first method decomposes faster than the other under identical conditions, and has a slightly lower energy of activation of 1.4 kcal/mole compared to 1.75 kcal/mole for the second. These differences are discussed in terms of the defect concentrations of the two azide samples.     

Oligoethylene Glycols as Highly Efficient Mutifunctional Promoters for Nucleophilic‐Substitution Reactions

Herein, we report the promising use of n‐oligoethylene glycols (oligoEGs) as mutifunctional promoters for nucleophilic‐substitution reactions employing alkali metal salts. Among the various oligoEGs tested, pentaethylene glycol (pentaEG) had the most efficient catalytic activity. In particular, when compared with other nucleophiles examined, a fluorine nucleophile generated from CsF was significantly activated by the pentaEG promoter. We also performed various facile nucleophilic‐displacement reactions, such as the halogenation, acetoxylation, thioacetoxylation, nitrilation, and azidation of various substrates with potassium halides, acetate, thioacetate, cyanide, and sodium azide, respectively, in the presence of the pentaEG promoter. All of these reactions provided their desired products in excellent yields. Furthermore, the combination of pentaEG and a tert‐alcohol medium showed tremendous efficiency in the nucleophilic‐displacement reactions (fluorination and methoxylation) of base‐sensitive substrates with basic nucleophiles (cesium fluoride and potassium methoxide, respectively). The catalytic role of oligoEGs was examined by quantum‐chemical methods. The oxygen atoms in oligoEGs were found to act as Lewis bases on the metal cations to produce the “flexible” nucleophile, whereas the two terminal hydroxy (OH) groups acted as “anchors” to orientate the nucleophile and the substrate into an ideal configuration for the reaction.     

以森田-贝里斯-希尔曼(MBH)碳酸酯为原料合成多取代1,4-二氢喹啉类衍生物

以森田-贝里斯-希尔曼(MBH)碳酸酯和活泼亚甲基类化合物为原料,在叔胺的催化下,经历两次亲核取代反应得到关键叠氮中间体,再与三苯基膦作用经连续的Staudinger反应、分子内aza-Wittig反应及异构化等,在温和的反应条件下合成了17个新的多取代1,4-二氢喹啉类衍生物.中间体及目标化合物均为新化合物,其结构均经红外光谱、高分辨质谱、核磁共振氢谱和核磁共振碳谱确证.     

A traceless solid-phase synthesis of pteridines

The linking of pyrimidines to polystyrene supports via either a 2- or 4-thioether provides access to pteridines through solid-phase synthesis. Oxidative cleavage (dimethyldioxirane) followed by nucleophilic substitution by amines, azide, or water completes a traceless synthesis of pteridines.     

Nickel azide photolysis

Photolysis of anhydrous NiN₆ at 30° under the action of high pressure Hg arc is reported. The sample for photolysis studies is prepared by treating aqueous nickel azide solution with excess of AnalaR dimethyl ketone. The pressure of N developed during photolysis under steady state conditions at constant intensity is a linear function oft ^1/2 and dark rate analysis suggests that the dependence ont ^1/2 should be due to the diffusion of N from reaction site to the surface of solid azide. Absence of photoconduction in the wavelength range of the irradiating radiation suggests that excitons are the reactive species and the linear dependence of the rate of photolysis on intensity is interpreted in terms of the reaction of a trapped exciton with adjacent azide ion.The authors are thankful to Mr. Etim, E. S. for technical assistance and to University of Calabar, Calabar, C.R.S., Nigeria for financial support.     

Synthesis and characterization of poly(isobutylene‐co‐isoprene)‐derived macro‐monomers

Allylic halide displacement from brominated poly(isobutylene‐co‐isoprene) (BIIR) by carboxylate nucleophiles is used to prepare elastomer derivatives containing pendant polymerizable functionality. These solvent‐borne substitutions are conducted under homogeneous and phase‐transfer catalyzed reaction conditions to synthesize acrylate and vinylbenzoate esters in high yield. The resulting macro‐monomer derivatives are shown to crosslink efficiently with peroxide initiation to give high modulus, thermoset products that cannot otherwise be accessed from isobutylene‐rich elastomers. The extent of cure, as measured by the storage modulus of the vulcanizate, scales with RCH=CH₂ content, and can be extended by co‐oligomerization of pendant unsaturation with that contained within multifunctional coagents. An alternate approach involving the introduction of pendant sulfonyl azide functionality is described, wherein thermal decomposition to nitrene intermediates supports an efficient crosslinking process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010