Substituent effects on the electrophotographic properties of N,N,N′,N′-tetraarylphenylenediamines 1a—i derivatives have been investigated to obtain a molecular design guide to enhance photosensitivity of hole transporting materials for organic photoreceptors. The introduction of methyl groups into N-substituted phenyl moiety in all the cases increases considerably the photosensitivity and reduc—es the residual potential, moreover, the m- and p-substitution was found to be the most promising. On the other hand, the presence of alkyl substituents enhances the stability of glassy state of such low molecular weight organic compounds.
A palladium-catalyzed cross-coupling reaction between the arylstannane 5c and the bicyclic vinyl bromide 3, which was obtained by a Diels—Alder reaction, provided the substituted bicyclo[2.2.2]octa-2,5-diene 6. A subsequent ozonolysis of the less substituted double bond of 6 followed by reduction of the intermediate with sodium borohydride provided the highly functionalized cyclohexene 8. This compound can be viewed as a substructure of the antitumor antibiotic dynemicin A.
Routes to diastereomers of constrained 4-amino-piperidines — a common pharmaceutically used diaminic building block — are realized mainly on the basis of CN-double bond species or their radicalic or anionic analogues. Kinetically controlled reactions on the one hand and thermodynamic control of reactions, reversible introduction of a repulsive group, direction of a reactant by intramolecular complexation, or involvement of radicalic or anionic intermediates with strong isomerization tendency on the other hand are the tools for a complementary accessibility of both diastereomers.
A new efficient method for the stereoselective preparation of trans-2,5-bis(alkyloxymethyl)pyrrolidines (7) using easily available starting materials is described. The main step of this synthesis is the stereoselective formation of the pyrrolidine ring by the 1,3-dipolar cycloaddition reaction of an in situ generated azomethine ylide. Both enantiomers of the C-2-symmetric auxiliaries are prepared separately in a short reaction sequence.
The aqueous solubilities (logS) of a set of 27 5-amino-1-aryl- 1H-tetrazoles with known biological activity were determined photometrically and correlated with their octan-1-ol/water partition coefficients (logP). The otained Linear relationship between logS and logP can be significantly improved by a melting point term, an electronic term and several indicator variables describing the deviating solubility behaviour of compounds with hydrogen bonding groups and the dependence on substituent position. The calculated more-parameter equations allow the reliable prediction of aqueous solubilities for 5-amino-1-aryl-1H-tetrazoles not yet synthesized or investigated.
Ten halogenated lunularins 16, 17, 26, 27, 30, 31, 36, 37, 42 and 43 as model substances for a new class of halometabolites isolated from bryophytes are prepared by chemical total syntheses according to a Wittig-protocol using halogenated aldehydes and phosphonium salts and/or by an in vitro halogenation of lunularin using potassium halide and hydrogen peroxide in the presence of a chloroperoxidase. The results confirm the need for a haloperoxidase in the in vitro chlorination of lunularin 6.
The classical Mannich reaction of aromatic methyl ketones with paraformaldehyde and dimethylamine hydrochloride resp. dimethyl(methylene)ammonium chloride has been extended to a few cases of 1-aryl-2-dimethylaminomethyl-prop-2-en-1-ones (ADMP reagents). They have gained remarkable attention in medicinal chemistry, but only more recently their properties as valuable building blocks for ring closure reactions to form either aroyl or dimethylaminomethyl substituted heterocyclic compounds has been evaluated. In this review, a collection of representative examples for their preparation (Scheme 2) and biological effects as well as the synthetic potential for the synthesis of heterocycles (Scheme 3—8) is given. The reaction of 4-hydroxycoumarin delivers with ADMP reagents, via the formation of detectable 3-(2-benzoylallyl)-4-hydroxycoumarins as secondary substitution products, after ring closure 3-benzoyl-3,4-dihy-dro-2H,5H-1-benzopyrano[4,3-b]pyran-5-ones (Scheme 4). The reaction of 4-hydroxy-6-methylpyran-2-one with ADMP reagents is investigated systematically in order to assess its suitability in carbon—carbon bond forming reactions as well as to provide the conditions for subsequent ring closure or intermolecular addition of further nucleophiles to the enone double bond of the intermediate 3-(2-benzoylallyl)-4-hy-droxy-6-methylpyran-2-ones yielding miscellaneous 3-substituted 2-pyrones (Scheme 5 and 8), and their application as building blocks for the combinatorial chemistry. The condensation of ADMP reagents with 2-aminopyridines gives rise to 3-benzoyl-3,4-dihydro-2H-pyrido[1,2-a]pyrimidines (Scheme 6) and the corresponding reaction using amidines affords 5-benzoyl-1,4,5,6-tetrahydropyrimidines (Scheme 7).
Four different disulfides, [2,2′-dithiobis-(2-mercaptoacetophenone)]-4-triphenylmethylthiosemicarbazone (1), [5,5′-dithiobis-(4-formyl-3-methyl-1-phenylpyrazole)]-4-triphenylmethylthiosemicarbazone (2), bis[1-(2-mercaptophenyl)-2-(4-(1-phenyl-3-methyl)pyrazole)-azaethene]di-sulfide (3) and bis[1-phenyl-2-(4-(1-phenyl-3-methyl-5-mercapto) pyrazole)-azaethene]disulfide (4) were synthesized by Schiff base reactions. Their electrochemical behaviour was examined by cyclic voltammetry. The results show low potentials for the disulfide reduction so that these compounds are suitable for the syntheses of tridentate thiolate ligands from disulfides by electrochemical cleavage. In addition compounds 2 and 4 were characterized by X-ray structure determination. The structures show significant differences of the S—S bonds and angles as compared to other disulfides without bulky substituents.
In a multistep process, anthracenide and both 1-benzoyl-2-methyl-3-phenylaziridines 1a form carbanion 4a that abstracts a proton from the solvent THF. The steep N pyramid of cis-1a makes attack of 4a on C=O of cis-1a fast enough to compete with proton abstraction while C=O of trans-1a with its flat and rapidly inverting pyramid did not react with 4a. The initially generated ketyls of 1a show another cis-trans effect of steric repulsion: their homolytic ring opening forms benzylic radical 3a, the precursor of carbanion 4a, but this opening is regiospecific for the cis ketyl only. The trans ketyl forms some isomeric radical too.
The design and synthesis of new materials are two key steps in the advancement of technology. One of the most promising approaches of development of new materials that combine advantages of organic polymers with those of inorganic solids is to devise polymers that have a backbone of inorganic atoms to which are attached organic side groups. Among the best developed examples of ‘inorganic–organic polymers’ are organosilicon polymers. The synthesis of new organosilicon polymers using silyl triflate intermediates is reviewed in this article. Protodephenylation of phenylated polysilanes as well as poly(silylenemethylenes) by triflic acid gave new functionalized compounds. Network polymers were obtained by reductive coupling of silyl triflates with potassium–graphite. Novel poly(silylenealkynes) and poly(silylenearylenes) containing a regular alternating arrangement of silylene groups and organic units were prepared from α,ω-bis[(trifluoromethyl)sulfonyloxysilyl]-substituted compounds and dinucleophiles. Some of the polymers are potential organic precursor for ceramic materials. The correlation between structure and thermolytic behavior is demonstrated on selected examples.
The influence of substitution on the absorption and Luminescence spectra of oligo(phenylenevinylene)s has been studied using distyrylbenzene (DSB) as a model compound. The degree, character, and pattern of substitution was varied systematically, altering the electronic properties of the DSB, the wavelength of the emitted light could be tuned over a range of 100 nm. The syntheses of 6b—h were performed by twofold Wittig Horner-olefinations of bisphoshonates 1a, b with substituted benzaldehydes 2a—i, 6i via Heck-reaction of the dibromosulfonylbenzene 3, 6k by Siegrist-reaction of 4 with N-phenylbenzaldimine and the Knoevenagel-reaction of benzyl cyanide with 5 led to 6l.
Journal für praktische ChemieVolume 342, Issue 3 p. 316-321 Reagent Copper(II) Triflate in Organic Synthesis Christian Hertweck Dr., Christian Hertweck Dr. hertweckcommat;u.washington.edu Search for more papers by this author Christian Hertweck Dr., Christian Hertweck Dr. hertweckcommat;u.washington.edu Search for more papers by this author First published: 03 April 2000 https://doi.org/10.1002/(SICI)1521-3897(200003)342:3<316::AID-PRAC316>3.0.CO;2-SCitations: 18AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume342, Issue3March 2000Pages 316-321 RelatedInformation
The push-pull functionalization of the ulose 1 to give the (E)-configurated dimethylaminomethylene pyranosidulose 2 was achieved with bis(dimethylamino)tert-butoxymethane. Substitution of the dimethylamino group by different amines provided the corresponding sugar enamines 3 as (Z) isomers. 2 reacted with hydrazine hydrate to furnish the pyrano[3,4-c]pyrazole 4. Treatment of 2 with acetamidine hydrochloride, benzamidine hydrochloride, S-methylisothiouronium methylsulfate and guanidine carbonate, respectively, in the presence of bases yielded the pyrimidoanellated pyranosides 5. Reaction of 2, ethyl 2-cyano-acetimidate hydrochloride 7 and sodium hydride afforded a mixture of a pyrido- and pyranoanellated pyranoside 9 and 10, respectively.
By coupling of aryldiazonium salts 5 with N,N-disubstituted 2-amino-5H-selenazoles 4 deeply coloured 5-arylazo-substituted 2-amino-selenazoles 6a-6l have been prepared and their solvatochromic properties deter-mined by means of UV/Vis spectroscopy, and compared with the ones of several other arylazosubstituted N,N'-dialkylanilines 7a-7d, 2-(N,N-dialkylamino)-thiophenes 8a-8e, and 2-(N,N-dialkylamino)-thiazoles 9a-9c.
γ-Fluoro-α, β-unsaturated carboxylic esters 7a, 7b and 7d and 4-fluoro-4-phenylbut-3-enoic ester (8) are obtained by two alternative pathways from 2-fluoro aldehydes 5a—d, either by Horner—Wadsworth—Emmons reaction or by Wittig reaction. The aldehydes 5a—d are prepared by Swern oxidation of the corresponding fluorohydrins 4a—d. These are available from α-olefins by bromofluorination, bromineby-acetate replacement and subsequent hydrolysis.
Journal für praktische ChemieVolume 342, Issue 2 p. 211-214 Reagent Bis alkoxytitanacyclopropanes and -propenes (Kulinkovich reagents): Versatile reagents for carbon—carbon bond formation Bernhard Breit Prof. Dr., Bernhard Breit Prof. Dr. bernhard.breitcommat;urz.uni-heidelberg.de Search for more papers by this author Bernhard Breit Prof. Dr., Bernhard Breit Prof. Dr. bernhard.breitcommat;urz.uni-heidelberg.de Search for more papers by this author First published: 31 January 2000 https://doi.org/10.1002/(SICI)1521-3897(200002)342:2<211::AID-PRAC211>3.0.CO;2-HCitations: 22AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume342, Issue2February 2000Pages 211-214 RelatedInformation
Reactions of hydrazonoyl halides 6 with either 4-amino-2,3-dihydro-6-substituted-3-thioxo-[1,2,4]-triazin-5(4H)ones 1(2) or 4-amino-3-methylthio-6-substituted-[1,2,4]-triazin-5(4H)ones 3(4) gave [1,2,4]-triazino-[4,3-b][1,2,4,5]tetrazine derivatives 9(10), respectively. The mechanism of the reactions studied is discussed.
Numerous reaction types in the field of iminium salts are performed in the gas-solid and solid-solid techniques in order to reach 100% yield. The stoichiometric runs are waste-free and do not require costly workup. Frequently, iminium salts were avoided, as acid catalysis was dispensable. Thioureas and α-halogenated ketones give a variety of 2-aminothiazoles via thiuronium salts in quantitative yield. A new intramolecular solid-state thermal condensation is reported. Enaminoketones are synthesized quantitatively from anilines and 1,3-diketones without catalysis and those can be used for quantitative solid-state 4-cascade reactions. Solid paraformaldehyde is used to produce methylene imines and internally trapped methylene iminium salts. Benzoylhydrazones are produced again without catalysis in the solid state. Vacuum and ball-mill techniques are particularly useful in the production of highly sensitive iminium salts. Hexahydro-1,3,5-triazines cyclorevert upon exposure to HCl gas to give solid arylmethylene iminium chlorides as new versatile reagents. These are used in arylaminomethylations of β-naphthol and of themselves to give Troeger's bases in 3-cascades. More direct are 4-cascade Troeger's base syntheses by dissolving hexahydro-1,3,5-triaryltriazines in trifluoroacetic acid. Alkylations of imines with trimethyloxonium tetrafluoroborate and triphenylmethyl cation give highly sensitive quaternary iminium salts in the ball-mill. The products are characterized by spectroscopic techniques and density functional theory (DFT) calculations at the B3LYP 6-31G* level. Molecular movements in the crystal and surface passivation are investigated with atomic force microscopy (AFM) techniques.
The preparation and the synthetic utility of the N-methoxy-N-methyl amides, also called as Weinreb amides, for the preparation of aldehydes and ketones has been discussed. Also the various reagents based on Weinreb′s amide has been compiled.
The reaction of BuSeLi, made from BuLi and elemental selenium, with chlorosilanes MexPhySiCl4-x-y led to selenobutyl substituted derivatives. In the cases of polychlorosilanes formation of the completely substituted products MexPhySi(SeBu)4-x-y are favoured. Higher yields of partially substituted products could be obtained by reaction of chlorosilanes with BuSeH/NEt3. Besides monosilanes the reactions of several methylchlorodi-, tri- and isotetrasilanes with BuSeLi and BuSeH/NEt3 were also investigated. In SiClMe(SiClMe2)2 the chlorine substituent at the middle silicon atom is substituted by BuSeH/NEt3 at first selectively. All products were characterized by 1H, 13C, 29Si and 77Se NMR and trends of chemical shifts and coupling constants (1JSiSi, 1JSiSe, 2JSiSe) with the substitution pattern were investigated.
