Syntheses of perfluorinated epoxides,diepoxides, and a novel rearrangement

t-Butylhydroperoxide/butyl-lithium is a good reagent for synthesis of epoxides and diepoxides from polyfluorinated-alkenes and-polyenes. This reagent and calcium hypochlorite both give a novel diepoxide 5 from perfluoro-3,4-dimethyl-2,4-diene 1; diepoxide 5 undergoes a novel rearrangement, at 200°C, to the corresponding 1,4-dioxine derivative 18. Possible mechanisms are discussed.     

Electronic control of stereoselectivity-21 : Stereochemical parallelism between dienophilic capture and singlet oxygenation of isodicyclopentadiene derivatives

The stereochemistry and product distribution resulting from reaction of 4',5',6',7'- tetrahydrospirol[cyclopropane-1,2']-[4,7]methano[2$\text{H}$]indene(5), endo-2-methyl(6a) and 2,2-dunethyl-4,7-dihydro-4,7-methano-2$\text{H}$-indene (6b), as well as 4',5',6',7'-tetrahydrospiro[cyclopentane-1,2']-[4,7]methano-[2$\text{H}$]indene (7) with singlet oxygen have been determined. Stereochemical assignments to the diepoxide products were readily deduced by ¹³C-NMR comparison with the spectra of the parent isomcrs of established structure (X-ray). To unravel the stereochemistry of the epoxy aldehydes, recourse was made to 2D NOE experiments The observed stereosclectivity and reaction profile of each substrate are analyzed and placed in proper mechanistic and energetic perspective.     

Structure of cryptocaryone : A constituent of Cryptocarya bourdilloni gamb.

From the roots of Cryptocarya bourdilloni, a new 5′,6′-dihydrochalcone, designated cryptocaryone, has been isolated. Based on spectral and degradative evidence, structure 2 has been proposed for cryptocaryone and confirmed by converting it to the hitherto unknown 5-carboxymethylflavone synthesized by a 6-step procedure from 7-methoxy-indan-1-one (4).     

Transformations thermiques des photooxydes meso des acenes—IV: Cas du photooxyde de naphtacene

Thermolysis of the naphthacene photooxide 10 leads to naphthacenequinone 11, to a bicyclic acetal 12, and to the cyclobutane diether 13. The isomerization involves a transient unstable meso diepoxide, 15 which can be trapped as the N-methylmaleimide adduct 18, but the behaviour of 15 differs appreciably from that of the analogous intermediate 5a. Chemical degradation evidence for structures of products is described; in particular a reduction of the diepoxidic adduct 18, which gives a 1–4 adduct, 33, of N-methylmaleimide with naphthacene differing from the meso adducts 36 (endo and exo). Analysis of the NMR spectra gives steric structures of all these derivatives.     

Stereoselective synthesis of pseudotripeptides incorporating uncommon bis-α-aminoacid derivatives and X-ray analysis. Part 3

Stereoselective synthesis of pseudotripeptides 4, 5, 6, 8, 9, 13 and 14, incorporating an uncommon bis(α-aminoacid) derivative, has been accomplished starting from the L-valine derived chiral synthon 1. The configuration of the introduced stereogenic centres has been assigned on the basis of ¹H NMR spectroscopic data. The geometry of the tripeptides, deduced on the basis of ¹H NMR parameters and IR spectra, was confirmed by X-ray crystal structure analysis of 6.     

Claisen rearrangements-XII : Synthesis of the coumarins, 5-methoxyseselin,trachyphyllin. coumurrayin and xanthoxyletin

The structure of the natural coumarins, 5-methoxyseselin 7 and trachyphyllin 14 have been confirmed by total syntheses from 7-acetoxy-5-prenyloxycoumarin 1 in good overall yields. Convenient synthetic routes to the natural coumarins, coumurrayin 4 and xanthoxyletin 10 have also been established.     

Synthetic studies on terpenic compounds—XV : Synthesis of methyl 14β-hydroxy-7β:8β,9β:11β,12α:13α-triepoxyabietan-18-oate,complete B/C ring model of antileukemic triptolides,from levopimaric acid

Stereospecific construction of the hydroxytriepoxide system present in triptolide 1 and tripdiolide 2 has been explored starting from levopimaric acid 3. 8α:14α:14α,12α:13α-Diepoxide 9 derived from 3 was converted to the epoxy dienone 16 by four steps process. The 9,11-epoxide group was introduced stereospecifically by oxidation with m-chloroperbenzoic acid to produce diepoxide 20. Epoxidation of the 14β-hydroxy derivative 33 with m-chloroperbenzoic acid or by a photochemical method afforded the title compound 36 which possesses the complete B/C ring functionality of 1 and 2. The stereochemistry of the epoxy rings in 36 was confirmed by X-ray crystallographic analysis of the isomeric triepoxide 37. The result of antitumor tests of the stereoisomeric epoxides obtained in this study is described.     

The constitution of the antibiotic trichoviridin

The antibiotic trichoviridin is shown to be an isontrile diepoxide with the relative stereochemistry (44).     

Kinetics of the acetic acid-catalysed ring-opening reaction of 2-phenyl-4,4-dimethyl-2-oxazolin-5-one with some aminoacid ethyl esters in carbon tetrachloride

The kinetic behaviour of the acetic acid-catalysed reaction of 2-phenyl-4,4-dimethyl-2-oxazolin-5-one (1) with the ethyl esters of glycine (2), dl-α-aminobutyric acid (4), α-aminoisobutyric acid (5), dl-norvaline (6), dl-valine (7), dl-leucine (8) and dl-phenylalanine (9) has been investigated. Within the concentration ranges employed the reactions follow second order kinetics, with no dependence of the experimental rate constant on the initial concentration of 1, just as found previously for the ethyl ester of dl-alanine. To explain the function of the catalyst a cyclic intermediate has been compared with other intermediates proposed for similar reactions. A good correlation has been obtained between the rate constant for the catalysed reaction and Taft's σ* values, showing that the effects of the substituents on the esters are mainly polar and supporting the structure of the proposed intermediate.     

Reaction of diazomethane with 5-hydroxy-4-phenylabonzofurazan as a synthetic route to derivatives of a new heterocycle—pyrazolo [3,4-f]-1,2,3-benzotriazole

Diazomethane adds to 5-hydroxy-4-phenylazobenzofurazan 1 giving a compound 3 which rearranges in alkaline solution to the 8-monoxime of 2-phenyl-5(6)H-pyrazolo [3,4-f]-1,2,3-benzotriazole-4,8-dione 4, the structure of which has been demonstrated by chemical and spectroscopic methods. The probable structure of adduct 3 is discussed on the basis of the chemical reactivity of the compound. The orientation of the cycloaddition and the dipolarophilic behaviour of the 6,7 double bond of the benzofurazan are interpreted on the basis of the quinone hydrazone struture of 1.     

Claisen rearrangements—VII : Novel reactions of the coumarin,tomentin

The structure of tomentin has been confirmed as 5-hydroxy-6,7-dimethoxycoumarin (2), the derived 3,3-dimethylallyl ether giving a para-Claisen rearrangement product. Relief of strain in the corresponding 1,1-dimethylallyl ether has been found to result in a novel regiospecific ortho-Claisen rearrangement occurring on silica at room temperature. The structure 18 of the stable ortho-dienone formed has been confirmed by conversion of the corresponding dehydrodienone (15), obtained from the rearrangement of tomentin 1,1-dimethylpropargyl ether, to alloxanthoxyletin (25).     

A new and efficient approach to pyrazolines. First synthesis of 3-aryl-5-dichloromethyl-2-pyrazolines

An efficient synthetic method for dichloromethylated pyrazolines has been established. 1-Aryl-4,4-dichlorobut-3-en-1-ones 4 were efficiently prepared by treatment of acetophenones with anhydrous chloral, followed by dehydration and reductive dechlorination. Compounds 4 reacted with hydrazine hydrate and methylhydrazine to give the respective 5-dichloromethyl-2-pyrazolines in high to quantitative yields. The molecular structure of 5-dichoromethyl-1-methyl-3-(2-naphthyl)-2-pyrazoline has been determined by X-ray crystallography.     

Synthesis of 3,9-dialkylguanines and their conversion into 3-alkylwyes,models for the fluorescent nucleosides from phenylalanine transfer ribonucleic acids

Synthesis of 3,9-dialkylguanines 5 has been accomplished by N-cyanation of 1-alkyl-5-(alkylamino)imidazole-4- carboxamides 3 followed by base-catalysed cyclisation. Cyclocondensation of 9-alkyl-3-methylguanines 5a, d, f with MeCOCH₂Br gave 3-alkylwyes 6, model compounds of the most probable structure for wyosine from Torulopsis utilis tRNA^Phe.     

Acyclic stereoselection. 28. Use of stereoselective aldol methodology in the total synthesis of cladinose.

Reactions of ($\text{S}$)-2-benzyloxypropanal (4) with the lithium, magnesium, and zirconium enolates of methyl 2-methoxypropanoate (1) and with ketene acetals 2 and 3 have been studied and the stereostructures of the resulting products elucidated. The major stereoisomer resulting from the metal enolate additions has been converted into the branched sugar cladinose (5).     

Synthesis,X-ray crystal structure,and properties of antipyrinium perchlorates,hexakis(antipyrine)thulium- and hexakis(antipyrine)ytterbium perchlorates. Quantum-chemical studies of ligands protonation

Protonation of the bioactive ligand-antipyrine (AP, 2,3-dimethyl-1-phenyl-3-pyrazolin-5-one) has been considered, the crystal packing specific features for the protonated antipyrine perchlorate compounds ([APH]ClO₄ · H₂O (1, 2) and [AP₂H]ClO₄ (3, 4)), as well as the crystal structure particularities for [Tm(AP)₆](ClO₄)₃ (5) and [Yb(AP)₆](ClO₄)₃ (6) have been elucidated. The protonation ability—complex formation ability relationship has been revealed for a number of organic ligands. Quantum-chemical calculations (DFT) and comparison with the experimental data allowed aligning some organic ligands in a row according to their ability to be protonated and to be incorporated into the inner coordination sphere of the complex.     

Claisen rearrangements-XIII : Synthesis of the natural coumarins,nordentatin, dentatin and clausarin

The structure of the natural coumarin, clausarin 10 has been confirmed by an eight-step synthesis from 5-hydroxyseselin 1 in 56%, overall yield. The efficient synthesis of its precursor, nordentatin 5 provides a convenient alternative synthetic route to dentatin 6. The revised structure 13 is suggested for clausenidinaric acid.     

Synthesis and biological evaluation of 4-thiazolidinone derivatives as antitubercular and antimicrobial agents

New series of N-[2-{2-(substitutedphenyl)-4-oxo-5-(substitutedbenzylidene)-1,3-thiazolidine}-iminoethyl]-2-amino-5-nitrothiazole, 5(a–m) have been synthesized from 2-amino-5-nitrothiazole as a starting material by conventional as well as microwave methods. All the synthesized compounds 4(a–m) were screened for their antibacterial and antifungal activities against some selected bacteria and fungi and antitubercular activity screened against Mycobacterium tuberculosis. The structure of all the synthesized compounds were confirmed by chemical and spectral analyses such as IR, ¹H NMR, ¹³C NMR and FAB-Mass.     

Regioselective protection of xylose for efficient synthesis of arabino-α-1,3-xylosides

We reported here an efficient regioselective protection strategy for xylose with two-step successive protections on 4- and 2-OH. This method enables the expeditious preparation of various xylose building blocks (3a–c, 5, 6). The rapid selective 2,4-protection especially facilitates the synthesis of 3-substituted xyloside structures. By this approach, typical arabino-α-1,3-xyloside disaccharide and trisaccharide, as fragment structure units from arabinoxylans, have been successfully synthesized.     

Hydrothermal synthesis of three-dimensional open-framework beryllium phosphites with 3,4-connected networks

Two new beryllium phosphites, H₂en·Be₃(HPO₃)₄ (1) and H₂pda·Be₃(HPO₃)₄ (2), have been synthesized under hydrothermal conditions. Single-crystal structural analyses reveal that both compounds have three-dimensional inorganic frameworks constructed from strictly alternating BeO₄ tetrahedra and HPO₃ pseudo pyramids. The structure of compound 1 can be described as a pillared layered structure with 12-ring channels. The structure of compound 2 has an interesting sqp topology if Be₃(HPO₃)₄ clusters are regarded as 5-connected nodes in the network.     

Neolemnane and eremophilane sesquiterpenoids from the pacific soft coral lemnalia africana

Two new sesquiterpenoids of the unprecedented neoiemnane ring system, and one eremophflane-derived sesquiterpene diol have been isolated from the pacific soft-coral Lemnalia africana. The structure of the novel neolemnane compounds, 4 and 5, were confirmed by X-ray crystallography, and the diol, 6, has been described based upon spectral analysis and chemical modification.