Modifications of Norditerpenoid Alkaloids: Ⅰ.N-Deethylation Reactions

Thenorditerpenoidandditerpenoidalkaloidsareagroupofhighl}oxygellatedandcomplexnaturalproducts.Theynotonlyhaveimportantpharnlacologicalactivitiessuchasanalgesic.localanesthetic,anti-inflammator}'andantiarrhythmetic'.butalso"la}'setoffalotofinterestingchemicalreactions'.Inordertosearchforhighactivit};.fox'..toxicitycompoundsandconversionoftheskeletons,wearecarryingoutthestructuremoditlcationsoftheaconitine-typenorditerpenoidalkaloids.Inthiscase,the,..l\l'deethviationisoneofthemostcommonreaction…     

Reactions of α-Sulfenyl-N-anions at the Nitrogen Atom. Reactions of N-Substituted Arenesulfenamide Sodium Salts with Isocyanates

N-Arylsulfonylarenesulfenamide sodium salts react with isocyanates in acetone to give N-arylsul- fonyl-N-arylsulfenyl-N'-substituted urea sodium salts which are converted into the corresponding ureas by the action of mineral acids.     

Chemical Modification of Kanamycin A. II. Nucleophilic Displacement Reactions of Kanamycin-A-4″-sulfonates

Abstract

Reactions of 2′,3′,4′,2″,6″-penta-O-acetyl-tetra-N-tert-butyloxycarbonyl-kanamycin-A-4″-brosylate (4b) or-4″-triflate (4c) with acetate, thiolacetate, azide, and fluoride, respectively, result in the formation of the corresponding derivatives of 4″-epi-kanamycin A (5a-d). While 4b invariably forms an elimination byproduct (9), the only side—reaction of 4c consists in a neighboring group attack with formation of a 3″-epi-4″-cyclic urethane (7). Removal of the protecting groups yields 4″-epi-(6a), 4″-thio-4″-epi-(6b), 4″-deoxy-4″-fluoro-4″-epi-(6d), 4″-azido-4″-deoxy-4″-epi-(6c), and after hydrogenation of the latter, 4″-amino-4″-deoxy-4″-epi-kanamycin A (6f).

Methyl 2,6-di-O-acetyl-3-amino-3-N-tert-butyloxycarbonyl-3-deoxy-4-O-triflyl-β-D-glucopyranoside (1b) served as a model to anticipate preparation, handling, and reactivity of 4c.     

Reactions of 3-(Β-hydroxyethyl)-8-thiaxanthine

Depending on the base used, reaction of 3-(-hydroxyethyl)-8-thiaxanthine with p-toluenesulfonylchloride either stops at the stage of formation of the tosylate or gives 1,2,5-thiadiazolo[3,4-d]oxazolidino[2,3-b]pyrimidin-9(4H)-one. Upon treatment with ammonia or methylamine, both of these compounds react to give 3-(-hydroxyethyl)-8-thiaguanines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 272–274, February, 1991.     

Reactions of γ-Sultines with Electrophilic Reagents. 3. Chlorination of 3,5-Diaryl-1,2-oxathiolane 2-Oxides

The influence of the nature of the aryl substituents and the reaction conditions for the chlorination of 3,5-diphenyl-1,2-oxathiolane 2-oxide and 3,5-bis(4-methoxyphenyl)-1,2-oxathiolane 2-oxide have been studied. Possible mechanisms for the chlorination of -sultines are discussed.     

The Reactions of Sydnone Compounds

The duality in electronic effect of sydnone ring and the effect of delocalization of 4-substitutedgroup to sydnone ring are investigated by the nitration of 3-benzyl-4-phenylsydnone and 4-formyl-3-arylsydnones. Sydnones are typical mesoionic compounds and their chemical, physical and biological properties     

Reactions of α-acetylenic ketones with n-3-amidinothioureas. 1. Synthesis and properties of new derivatives of 1,3-thiazine

[4-Phenyl-2H-1,3-thiazin]-2-ylideneguanidinium perchlorate or acetoxytrifluoroborate respectively was obtained from the reaction of benzoylacetylene with N-amidinothiourea in glacial AcOH in the presence of an equimolar quantity of HClO₄ or BF₃Et₂O. These compounds underwent hydrolysis at the amidine unit on treatment with acid or base. For example, the perchlorate on heating in HClO₄ was converted into 2-imino-4-phenyl-2H-1,3-thiazinium perchlorate, while treatment with aqueous NaOH in DMSO gave the free base - 6-phenyl-1,2-dihydropyrimidine-2-thione.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1848–1852, December, 2004.     

Preparation and Reactions of Octasilsesquioxanes

Because of the length scales involved, nanocomposite materials incorporate extensive interfacial interactions that can result in non-linear changes in the composite property. Chemists often start from polymerizable inorganic and organic constituents in the molecule to build organic/inorganic hybrids that combine advantageous properties of disparate components. Silsesquioxanes (RSiO1.5)n, derived from e.g. RSiCl3 or RSi(OEt)3 by hydrolysis/condensation in a sol-gel process, are a class of s…     

Polybromocyclopentadienes in Diels–Alder Reactions. Reactions of Hexabromo- and 5,5-Dimethoxytetrabromo-1,3-cyclopentadienes with para-Substituted Allyl Benzoates

The Diels–Alder reaction of hexabromo- and 5,5-dimethoxytetrabromo-1,3-cyclopentadienes with para-substituted allyl benzoates occurs with high stereoselectivity, yielding the corresponding endo adducts. The kinetics of this reaction were studied, and its activation parameters were determined. The reaction is favored by the presence of both electron-donor and electron-acceptor substituents in the aromatic ring. The diene–dienophile system was assumed to react according to the neutral pattern.     

Preparation and Reactions of Thiazole-fused 3-Sulfolenes. Useful Precursors to o-Dimethylene Thiazoles

Thiazole-fused 3-sulfolenes 6 and 7 have been efficiently prepared from 4-bromo-3-sulfolanone 5 in one step. These 3-sulfolenes react as synthetic equivalents to o-dimethylene thiazoles.     

Selective Substitution Reactions on PVC. Lability of Some “Normal” Structures

The nucleophilic substitution reaction on PVC with sodium thiophenate in cyclohexanone solution is studied. The reaction appears to be S_N2 substitution and it involves three different steps with decreasing reaction constants. By using ¹³C-NMR spectroscopy, the fast step is proposed to be due to the high reactivity of the central chlorine in isotactic triads and, to a lesser extent, in heterotactic triads. The study of the thermal degradation of the modified samples shows that during the fast step of substitution a stabilizing effect occurs, and that as soon as the first step is over, the polymer stability decreases markedly. These effects are accompanied by changes in poly-ene distribution as proved by UV-VIS absorption spectroscopy study on degraded samples. The results, as discussed on the basis of the possible conformations of triads in PVC, suggest that some chlorine atoms in both the GTTG isotactic and the TTTG heterotactic triads should be considered as labile structures in PVC. It follows from the results obtained that on the one hand the initiation of degradation may occur by normal structures, and on the other the build-up of polyenes is favored by the presence of …TTTT… sequences. Both features contributing to a better understanding of the degradation of PVC.     

Reactions of transition metal σ-acetylides: VIII. Preparation and properties of some aryldiazo-vinylidene complexes

Fourteen aryldiazovinylidene complexes of ruthenium and osmium have been made by addition of aryldiazonium cations to the appropriate σ-acetylides. Their properties and spectra (including FAB-MS) are described, and reactions with MeOH, hydride and methoxide are reported. Addition to and protonation, alkylation, and cyclomanganation of the aryldiazo functions are also described.     

Reactions of α-nitroacrylates with thiophenols

Reactions of α-nitroacrylates with aromatic thiols like 4-methyl- and 4-chlorothiophenols afford a series of new 3-arylsulfanyl-2-nitropropanoates. The latter were isolated as diastereomerically pure substances or mixtures of two diastereomers. Structures of the obtained S-adducts were confirmed by IR, ¹H and ¹³C-{¹H} NMR spectroscopy using HMQC and HMBC experiments.     

The Chemical Reactions of 11-Hydroxycephalotaxine

1l-HydroxycephalotaxinelisoneofthethreeC,,-oxygenatedalkaloidsisolatedfromthegenusCePhalotaxus.Onlyafewreportsonthechemicaland,biologicalactivityandderivationsoflwerefoundl-3.Someofthechemicalreactionsofll-hydroxy-cephalotaxinel,whichwereencounteredduringthederivationoflandtherelatedcompoundsweredescribedinthispaPeLAcetylationoflwithlessthantwomolarofaceticanhydrideformedtWomonoacetateA,(C,-acetate)andB,(C,,-acetate)infavorofC,,acetylationduetothestericdifference(AandBstridthosecomPOunds…     

Reactions of α-halonitrosoalkanes with resorcinol

-Halonitrosoalkanes react with resorcinol as nitrosylating agents to form 3-hydroxy-N-(2,4-dihydroxyphenyl)-1,4-quinone imine.Translated fromIzvestiya Akademioi Nauk. Seriya Khimicheskaya, No. 3, pp.773–774, March, 1996.     

Catalysis of Carbon–Gas Reactions

The characteristic features on the catalysis of carbon–gas reactions has been studied by combining various techniques such as transient kinetics, temperature-programmed desorption and others. Some of recent achievements are presented to comprehend the state of the art. Many industrial processes associated with catalytic carbon–gas reactions are then discussed in relation to the fundamental chemistry of catalysis.     

Stereoselective Reactions of δ2-Isoxazoline Exo-azaenolates. A Model for Construction of the C-Ring of Sesbanimide A

A Stereoselective aldol reaction between bis(tert-butyldimethylsilyloxy) acetone and an isoxazoline-derived azaenolate is a key step in the construction of a C-ring model of sesbanimide A.     

Acceleration of Organic Reactions Using Microwave

The use of microwave technology in accelerating organic reactions has received intense attention leading to immense growth recently. Accordingly, we have been interested in improving the efficacy of organic processes by microwave irradiation. Here we report our results on the microwave assisted direct amide formation from carboxylic acid and amine, the hydrolysis of biopolymers, and nucleophilic aromatic substitution reaction. The reactions carried out under microwave irradiation, in general, …     

Reactions of magnesium formate on supports

Thermal decomposition of supported magnesium formate has been studied by gas chro-matography.The reaction paths of decomposition of supported magnesium formate depend on thenature of the supports.For Mg(HCO_2)_2/HZSM-5,the zeolite behaves as a dehydration catalyst togive CO and H_2O at lower temperatures;when the zeolite is modified by phosphorus,the methanationreaction will be partly restrained.In the case of Mg(HCO_2)_2/AC,strong adsorption of CO_2 leadsto the formation of the shoulder peak of CO_2 at higher temperatures,however,CH_4 disappears aftermodified by phosphorus.For Mg(HCO_2)_2/Al_2O_3,the dehydrogenation of HCO_2~- takes place on thesurface of Al_2O_3.The decomposition of Mg(HCO_2)_2 on SiO_2 in hydrogen yields two peaks of COand only one appears after modified by phosphorus.When Mg(HCO_2)_2 decomposes on MgO,the firstpeak of CO_2 arises from the reaction of surface Mg~(2+) with HCO_2~- from dissociated Mg(HCO_2)_2.