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Synthons
Kinds of Synthons Selected AbstractsA New 2H -Azirin-3-amine as a Synthon for 2-MethylaspartateHELVETICA CHIMICA ACTA, Issue 11 2005Kathrin The synthesis of a novel 2,2-disubstituted 2H -azirin-3-amine 3a as a building block for racemic Asp(2Me) is described. This synthon contains an ester group in the side chain. The reaction of 3a with thiobenzoic acid and the amino acid Z-Val-OH yielded the racemic monothiodiamide 10a and the dipeptide 11 as a mixture of diastereoisomers, respectively (Scheme,2). In 11, each of the protecting groups was removed selectively (Scheme,3). First attempts toward the preparation of enantiomerically pure synthons for Asp(2Me) with a chiral auxiliary group in the side chain are described. Synthons 3b with a 1-(naphthalen-1-yl)ethyl ester group and 3c with a menthyl ester group were prepared and reacted with thiobenzoic acid to form monothiodiamides 10b and 10c (Scheme,2). However, the diastereoisomers of the synthons 3b and 3c could not be separated by chromatography. [source] The Nonchiral Bislactim Diethoxy Ether as a Highly Stereo-Inducing Synthon for Sterically Hindered, , -Branched , -Amino Acids: A Practical, Large-Scale Route to an Intermediate of the Novel Renin Inhibitor AliskirenHELVETICA CHIMICA ACTA, Issue 8 2003Richard Göschke The diastereoselective synthesis of the sterically hindered, , -branched , -amino acid derivative (2S,4S)- 24a and its N -[(tert -butoxy)carbonyl](Boc)-protected alcohol (2S,4S)- 19, both key intermediates of a novel class of nonpeptide renin inhibitors such as aliskiren (1), is described. Initially, the analogous methyl ester (2S,4S)- 17 was obtained by alkylation of the chiral Schöllkopf dihydropyrazine (R)- 12a with the dialkoxy-substituted alkyl bromide (R)- 11a, which proceeded with explicitly high diastereofacial selectivity (ds ,98%) to give (2S,5R,2,S)- 13a (Scheme,4), followed by mild acid hydrolysis and N -Boc protection (Scheme,5). Conversely, the complete lack of stereocontrol and poor yields for the reaction of (R)- 11a with the enantiomeric (S)- 12b suggested, in addition to the anticipated shielding effect by the iPr group at C(2) of the auxiliary, steric repulsion between the MeOC(6) and the bulky residues of (R)- 11a in the proposed transition state, which would strongly disfavor both the Si and Re attack of the electrophile (see Fig.). Based on this rationale, alkylation of the readily accessible achiral diethoxy-dihydropyrazine 21 with (R)- 11a was found to provide a 95,:,5 mixture of diastereoisomers (2S,2,S)- 22a and (2R,2,S)- 23a in high yield (Scheme,6), which afforded in two steps and after recrystallization enantiomerically pure (2S,4S)- 24a. Similarly, the stereochemical course for the alkylation reactions of the related alkyl bromides (S)- 28a and (R)- 28b with both (R)- 12a and (S)- 12b as well as with the achiral 21 was investigated (Schemes,7,9). The precursor bromides (R)- 11a, (S)- 11b, (R)- 28a, and (S)- 28b were efficiently synthesized via the diastereoselective alkylation of the Evans 3-isovaleroyloxazolidin-2-ones (R)- 7a and (S)- 7b either with bromide 6 or with benzyl chloromethyl ether, and subsequent standard transformations (Schemes,3 and 7). A practical and economical protocol of the preparation of (2S,4S)- 24a on a multi-100-g scale is given. This is the first report of the application of an achiral dihydropyrazine, i.e., in form of 21, as a highly stereo-inducing synthon providing rapid access to a N -protected , -branched , -amino acid with (2S) absolute configuration. [source] Ethyl-3,4-diaroyl-2-cyanobutyrate: A Synthon for novel heterocyclesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2009Adivireddy Padmaja A new class of aminopyrazolones, aminoisoxazolones, aminopyrimidinones, and thioxopyrimidinones were synthesized from Michael adduct, ethyl-3,4-diaroyl-2-cyanobutyrate, on reaction with different nucleophiles, hydrazine hydrate, hydroxylamine hydrochloride, and urea derivatives. J. Heterocyclic Chem., (2009). [source] Shuttling P3 from Niobium to Rhodium: The Synthesis and Use of Ph3SnP3(C6H8) as a P3, Synthon,ANGEWANDTE CHEMIE, Issue 9 2010Brandi Anatomie eines P3, -Synthons: Das Ph3SnP3(C6H8)-Molekül (siehe Bild; Sn,rot, P,orange) wurde durch Triphosphortransfer von einem Niob-Komplex synthetisiert und dient als nützliches P3, -Reservoir. Die Behandlung von Ph3SnP3(C6H8) mit dem Wilkinson-Katalysator, [ClRh(PPh3)3], führte unter Abspaltung von Ph3SnCl und 1,3-Cyclohexadien zum neuen Cyclo-P3 -Komplex [(,3 -P3)Rh(PPh3)3]. [source] ChemInform Abstract: Palladium-Catalyzed Annulation of Haloanilines and Halobenzamides Using Norbornadiene as an Acetylene Synthon: A Route to Functionalized Indolines, Isoquinolinones, and Indoles.CHEMINFORM, Issue 27 2009Praew Thansandote Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Fused Polyaza-heterocycles and 1,3,4-Thiadiazoles via a Tricyano Synthon.CHEMINFORM, Issue 19 2008Kamal M. Dawood Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Highly Stereoselective Synthesis of Perhydropyran[2,3-b]pyrans from the New 3-Methylidenepentane-1,5-dianion Synthon.CHEMINFORM, Issue 36 2006Francisco Alonso Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Azetidin-2,3-dione Synthon for Stereoselective Synthesis of cis- and trans-C-3-Alkyl/Aryl Azetidin-2-ones.CHEMINFORM, Issue 20 2006Dharmendra Kumar Tiwari Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] The Nonchiral Bislactim Diethoxy Ether as a Highly Stereo-Inducing Synthon for Sterically Hindered, ,-Branched ,-Amino Acids: A Practical, Large-Scale Route to an Intermediate of the Novel Renin Inhibitor Aliskiren.CHEMINFORM, Issue 50 2003Richard Goeschke Abstract For Abstract see ChemInform Abstract in Full Text. [source] 1,3-Dichloro-2-butene: A Useful Precursor for the 2-Butene-1,3-dianion and Its Corresponding 1,3-Dipolar Synthon.CHEMINFORM, Issue 42 2003Miguel Yus No abstract is available for this article. [source] 1-Bis(methoxy)-4-bis(methylthio)-3-buten-2-one: Useful Three Carbon Synthon for Synthesis of Five and Six Membered Heterocycles with Masked (or Unmasked) Aldehyde Functionality.CHEMINFORM, Issue 32 2003Pranab K. Mahata Abstract For Abstract see ChemInform Abstract in Full Text. [source] 6-Chloro-2(2H)-pyranone: A New 2(2H)-Pyranone Synthon.CHEMINFORM, Issue 16 2003Matteo Biagetti Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: A Useful Chiral Synthon from (R)-4-Menthenone.CHEMINFORM, Issue 2 2002R. Ya. Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Towards Selective Recognition of Sialic Acid Through Simultaneous Binding to Its cis -Diol and Carboxylate FunctionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2010Martín Regueiro-Figueroa Abstract A series of receptors containing phenylboronic acid and urea or thiourea units have been designed for simultaneous recognition of the cis -diol and carboxylate functions of sialic acids, which are known to be overexpressed on the surfaces of tumor cells. The interaction of the receptors with 5-acetylneuraminic acid (Neu5Ac) and 2-,- O -methyl Neu5Ac (MeNeu5Ac) in DMSO solution has been investigated bymeans of spectrophotometric titrations and 1H, 13C, and 11B NMR spectroscopy. Additionally, we have also investigated the binding of these receptors with competing monosaccharides such as D -(+)-glucose, D -fructose, methyl ,- D -galactoside, and methyl ,- D -mannoside. Our results show that 2-{[3-(4-nitrophenyl)thioureido]methyl}phenylboronic acid (3a) recognizes both Neu5Ac and MeNeu5Ac with good selectivity with regard to the remaining monosaccharides investigated. DFT calculations performed at the B3LYP/6-31G(d) level show that this selectivity is due to a cooperative two-site binding of Neu5Ac through 1) ester formation by interaction at the phenylboronic acid function of the receptor and 2) hydrogen-bond interaction between the thiourea moiety and the carboxylate group of Neu5Ac. Compound 3a can therefore be considered a promising synthon for the design of contrast agents for magnetic resonance imaging of tumors. In contrast, the analogue of 3a containing a urea moiety , compound 3b , displays strong binding to all monosaccharides investigated, due to two-site binding through interaction on the phenylboronic acid function of the receptor and a hydrogen-bond interaction between the urea moiety and the sugar hydroxy groups. [source] The Synthesis, Photophysical Characterization, and X-Ray Structure Analysis of Two Polymorphs of 4,4,-DiacetylstilbeneHELVETICA CHIMICA ACTA, Issue 6 2010Cameron Pye Abstract A palladium(II) acetate-catalyzed synthesis of 1 that utilizes the novel triazene 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption spectra of 1 in various solvents exhibited a ,,,* transition in the range of 330,350,nm. Compound 1 was observed to be luminescent, with room-temperature solution and solid-state emission spectra that exhibited maxima in the range 400,500,nm. All room-temperature absorption and emission spectra exhibited some degree of vibrational structure. The emission spectrum of 1 at 77,K in propanenitrile glass was broad and featureless with a maximum at 447,nm. Compound 1 crystallized as a yellow and colorless polymorph. X-Ray structure analyses of both of these polymorphs and 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone are presented. [source] A New 2H -Azirin-3-amine as a Synthon for 2-MethylaspartateHELVETICA CHIMICA ACTA, Issue 11 2005Kathrin The synthesis of a novel 2,2-disubstituted 2H -azirin-3-amine 3a as a building block for racemic Asp(2Me) is described. This synthon contains an ester group in the side chain. The reaction of 3a with thiobenzoic acid and the amino acid Z-Val-OH yielded the racemic monothiodiamide 10a and the dipeptide 11 as a mixture of diastereoisomers, respectively (Scheme,2). In 11, each of the protecting groups was removed selectively (Scheme,3). First attempts toward the preparation of enantiomerically pure synthons for Asp(2Me) with a chiral auxiliary group in the side chain are described. Synthons 3b with a 1-(naphthalen-1-yl)ethyl ester group and 3c with a menthyl ester group were prepared and reacted with thiobenzoic acid to form monothiodiamides 10b and 10c (Scheme,2). However, the diastereoisomers of the synthons 3b and 3c could not be separated by chromatography. [source] The Nonchiral Bislactim Diethoxy Ether as a Highly Stereo-Inducing Synthon for Sterically Hindered, , -Branched , -Amino Acids: A Practical, Large-Scale Route to an Intermediate of the Novel Renin Inhibitor AliskirenHELVETICA CHIMICA ACTA, Issue 8 2003Richard Göschke The diastereoselective synthesis of the sterically hindered, , -branched , -amino acid derivative (2S,4S)- 24a and its N -[(tert -butoxy)carbonyl](Boc)-protected alcohol (2S,4S)- 19, both key intermediates of a novel class of nonpeptide renin inhibitors such as aliskiren (1), is described. Initially, the analogous methyl ester (2S,4S)- 17 was obtained by alkylation of the chiral Schöllkopf dihydropyrazine (R)- 12a with the dialkoxy-substituted alkyl bromide (R)- 11a, which proceeded with explicitly high diastereofacial selectivity (ds ,98%) to give (2S,5R,2,S)- 13a (Scheme,4), followed by mild acid hydrolysis and N -Boc protection (Scheme,5). Conversely, the complete lack of stereocontrol and poor yields for the reaction of (R)- 11a with the enantiomeric (S)- 12b suggested, in addition to the anticipated shielding effect by the iPr group at C(2) of the auxiliary, steric repulsion between the MeOC(6) and the bulky residues of (R)- 11a in the proposed transition state, which would strongly disfavor both the Si and Re attack of the electrophile (see Fig.). Based on this rationale, alkylation of the readily accessible achiral diethoxy-dihydropyrazine 21 with (R)- 11a was found to provide a 95,:,5 mixture of diastereoisomers (2S,2,S)- 22a and (2R,2,S)- 23a in high yield (Scheme,6), which afforded in two steps and after recrystallization enantiomerically pure (2S,4S)- 24a. Similarly, the stereochemical course for the alkylation reactions of the related alkyl bromides (S)- 28a and (R)- 28b with both (R)- 12a and (S)- 12b as well as with the achiral 21 was investigated (Schemes,7,9). The precursor bromides (R)- 11a, (S)- 11b, (R)- 28a, and (S)- 28b were efficiently synthesized via the diastereoselective alkylation of the Evans 3-isovaleroyloxazolidin-2-ones (R)- 7a and (S)- 7b either with bromide 6 or with benzyl chloromethyl ether, and subsequent standard transformations (Schemes,3 and 7). A practical and economical protocol of the preparation of (2S,4S)- 24a on a multi-100-g scale is given. This is the first report of the application of an achiral dihydropyrazine, i.e., in form of 21, as a highly stereo-inducing synthon providing rapid access to a N -protected , -branched , -amino acid with (2S) absolute configuration. [source] Fused quinoline heterocycles VI: Synthesis of 5H -1-thia-3,5,6-triazaaceanthrylenes and 5H -1-thia-3,4,5,6-tetraazaaceanthrylenesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2005Ramadan Ahmed Mekheimer Ethyl 3-amino-4-chlorothieno[3,2-c]quinoline-2-carboxylate (4) is a versatile synthon, prepared by reacting an equimolar amount of 2,4-dichloroquinoline-3-carbonitrile (1) with ethyl mercaptoacetate (2). Ethyl 5-alkyl-5H -1-thia-3,5,6-triazaaceanfhrylene-2-carboxylates 9a-c, novel perianellated tetracyclic heteroaro-matics, were prepared by refluxing 4 with excess of primary amines 7a-c to yield the corresponding amino-thieno[3,2-c]quinolines 8a-c. Subsequent reaction with an excess of triethyl orthoformate (TEO) furnished 9a-c. Reaction of 4 with TEO in Ac2O at reflux, gave the simple acetylated compounds, thieno[3,2- c]-quinolines 12 and 13. Refluxing 4 with benzylamine (7d) gave 10, and subsequent treatment with TEO gave the tetracyclic compound 11. Refluxing 13 with an excess of alkylamines 7a-d gave the fhieno[3,2- c]quino-lines 15. Refluxing the aminothienoquinolines 8b with an excess of triethyl orthoacetate gave thieno[3,2- c]quinoline 17, while heating with Ac2O gave 18 and 19, with small amounts of 16. Reaction of 8a,b with ethyl chloroformate and phenylisothiocyanate generated the new 1-thia-3,5,6-triazaaceanthrylenes 20a,b and 21a,b, respectively. Diazotization of 8a-c afforded the novel tetracyclic ethyl 5-alkyl-5H -1-fhia-3,4,5,6-tetraazaaceanthrylene-2-carboxylates 22a-c in good yields. [source] MALDI-TOF mass spectrometric analysis for the characterization of the 5,10,15,20-tetrakis- (m -hydroxyphenyl)bacteriochlorin (m -THPBC) photoproducts in biological environmentJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2005Henri-Pierre Lassalle Abstract Photoproducts formation upon irradiation (739 nm) of 5,10,15,20-tetrakis(m -hydroxyphenyl)bacteriochlorin (m -THPBC) in phosphate buffer saline (PBS) supplemented with human serum albumin (HSA) were studied by means of absorption spectroscopy and MALDI-TOF mass spectrometry. The experiments were performed with a freshly prepared PBS,HSA solution of m -THPBC and with a PBS,HSA m -THPBC solution incubated for 6 h at 37 °C. The incubation of m -THPBC solution leads to the dye monomerisation, whereas in the freshly prepared solution, m -THPBC is under an aggregated form. Regardless of the incubation condition, photobleaching experiments carried out by absorption spectroscopy demonstrate the degradation of the photosensitizer and its phototransformation in m -THPC. Moreover, m -THPC was the sole photoproduct detected using absorption spectroscopy. Together with a degradation of m -THPBC and formation of m -THPC, MALDI-TOF mass spectrometry evidenced several other photoinduced modifications. Photoproducts such as dihydroxy m -THPBC and dihydroxy m -THPC were detected in both conditions; however, the formation of hydroxylated photoproducts was significantly greater in incubated solution. In addition, small molecules arising from the degradation of the photosensitizer and identified as dipyrin derivatives and dipyrrolic synthon were observed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Conformational polymorphism in a Schiff-base macrocyclic organic ligand: an experimental and theoretical studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2010Leonardo Lo Presti Polymorphism in the highly flexible organic Schiff-base macrocycle ligand 3,6,9,17,20,23-hexa-azapentacyclo(23.3.1.111,15.02,6.016,20)triaconta-1(29),9,11,13,15(30),23,25,27-octaene (DIEN, C24H30N6) has been studied by single-crystal X-ray diffraction and both solid-state and gas-phase density functional theory (DFT) calculations. In the literature, only solvated structures of the title compound are known. Two new polymorphs and a new solvated form of DIEN, all obtained from the same solvent with different crystallization conditions, are presented for the first time. They all have symmetry, with the macrocycle positioned on inversion centres. The two unsolvated polymorphic forms differ in the number of molecules in the asymmetric unit Z,, density and cohesive energy. Theoretical results confirm that the most stable form is (II°), with Z, = 1.5. Two distinct molecular conformations have been found, named `endo' or `exo' according to the orientation of the imine N atoms, which can be directed towards the interior or the exterior of the macrocycle. The endo arrangement is ubiquitous in the solid state and is shared by two independent molecules which constitute an invariant supramolecular synthon in all the known crystal forms of DIEN. It is also the most stable arrangement in the gas phase. The exo form, on the other hand, appears only in phase (II°), which contains both the conformers. Similarities and differences among the occurring packing motifs, as well as solvent effects, are discussed with the aid of Hirshfeld surface fingerprint plots and correlated to the results of the energy analysis. A possible interconversion path in the gas phase between the endo and the exo conformers has been found by DFT calculations; it consists of a two-step mechanism with activation energies of the order of 30,40,kJ,mol,1. These findings have been related to the empirical evidence that the most stable phase (II°) is also the last appearing one, in accordance with Ostwald's rule. [source] Planar packing of tetrachlorodicyanobenzenes.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2009Equimolar mixtures of ortho - and meta -, or ortho - and para -, or meta - and para -tetrachlorodicyanobenzene, C6Cl4(CN)2, form structures with disordered layers containing both kinds of molecules in rhombohedral or pseudo-rhombohedral cells. These structures are similar to the structure of the rhombohedral form of the meta isomer. The guiding force appears to be an intermolecular synthon, in which a nitrile group in one molecule interacts with Cl atoms in two adjacent molecules with N...Cl distances of approximately 3.1,Å. [source] Basic forms of supramolecular self-assembly organized by parallel and antiparallel hydrogen bonds in the racemic crystal structures of six disubstituted and trisubstituted cyclopentane derivativesACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2001Alajos Kálmán A selection of stereoisomeric 2-hydroxy-1-cyclopentanecarboxamides, a 4- tert -butyl derivative and three tert -butyl derivatives of the respective carboxylic acid were subjected to X-ray crystallography. The optically active molecules (I),(VI) form racemic crystals. Each racemic structure is basically determined by two intermolecular hydrogen bonds of O,H,O=C,XH and O=C,X,H,OH types (X = O, NH). The partially similar patterns of close packing observed reflect five basic forms of supramolecular self-assembly. In the racemic crystals of chiral molecules, there are homo- and heterochiral chains of molecules formed by the principal (O,H,O=C) hydrogen bonds. These chains assemble either in a parallel or antiparallel mode. The parallel homochiral chains (hop) observed in structure (II), (1R*,2R*)-2-hydroxy-1-cyclopentanecarboxamide, demand the polar space group Pca21, while the parallel heterochiral chains (hep) are organized in antiparallel layers with space group P21/n in structure (VI), (1R*,2S*,5R*-5- tert -butyl-2-hydroxy-1-cyclopentanecarboxylic acid). Heterochiral chains in an antiparallel array (hea) are found in (I), (1R*,2S*)-2-hydroxy-1-cyclopentanecarboxamide, and (V) [(1R*,2S*4S*)-4- tert -butyl-2-hydroxy-1-cyclopentanecarboxylic acid, space group P21/c]. Structures (IV), (1R*,2S*,4R*)-4- tert -butyl-2-hydroxy-1-cyclopentanecarboxylic acid, and (III), (1R*,2R*,4S*)-4- tert -butyl-2-hydroxy-1-cyclopentanecarboxamide, reveal that homochiral chains in an antiparallel array (hoa; cross-linked by heterochiral dimers held together by the second hydrogen bonds) can be formed by either translation (space group P) or a screw axis (space group P21/c). These alternatives are denoted hoa1 and hoa2. Similarly, within each pattern (hea, hep and hop) two slightly different alternatives can be expected. The partial similarities in the identified five patterns of hydrogen bonding are described by graph-set notations. Structures (I), (IV) and (V) can be characterized by a common supramolecular synthon, while the highest degree of similarity is shown by the isostructurality of (I) and (V). [source] Probing the supramolecular interaction synthons of 1-benzofuran-2,3-dicarboxylic acid in its monoanionic formACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Rajesh Koner 1-Benzofuran-2,3-dicarboxylic acid (C10H6O5) is a dicarboxylic acid ligand which can readily engage in organometallic complexes with various metal ions. This ligand is characterized by an intramolecular hydrogen bond between the two carboxyl residues, and, as a monoanionic species, readily forms supramolecular adducts with different organic and inorganic cations. These are a 1:1 adduct with the dimethylammonium cation, namely dimethylammonium 3-carboxy-1-benzofuran-2-carboxylate, C2H8N+·C10H5O5,, (I), a 2:1 complex with Cu2+ ions in which four neutral imidazole molecules also coordinate the metal atom, namely bis(3-carboxy-1-benzofuran-2-carboxylato-,O3)tetrakis(1H -imidazole-,N3)copper(II), [Cu(C10H5O5)2(C3H4N2)4], (II), and a 4:1 adduct with [La(H2O)7]3+ ions, namely heptaaquabis(3-carboxy-1-benzofuran-2-carboxylato-,O3)lanthanum 3-carboxy-1-benzofuran-2-carboxylate 1-benzofuran-2,3-dicarboxylic acid solvate tetrahydrate, [La(C10H5O5)2(H2O)7](C10H5O5)·C10H6O5·4H2O, (III). In the crystal structure, complex (II) resides on inversion centres, while complex (III) resides on axes of twofold rotation. The crystal packing in all three structures reveals ,,, stacking interactions between the planar aromatic benzofuran residues, as well as hydrogen bonding between the components. The significance of this study lies in the first crystallographic characterization of the title framework, which consistently exhibits the presence of an intramolecular hydrogen bond and a consequent monoanionic-only nature. It shows further that the anion can coordinate readily to metal cations as a ligand, as well as acting as a monovalent counter-ion. Finally, the aromaticity of the flat benzofuran residue provides an additional supramolecular synthon that directs and facilitates the crystal packing of compounds (I),(III). [source] Hexagonal packing of cis,cis -cyclohexane-1,3,5-tricarboxamideACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2007Binoy K. Saha The title compound, C9H15N3O3, which has crystallographically imposed threefold symmetry, crystallizes as a hexagonal columnar structure. The crystal structure is stabilized by a less common amide,amide synthon, where one amide group is hydrogen bonded to four others. The amide groups form cyclic amide,amide hexamers via N,H...O hydrogen bonds. [source] Van der Waals and Polar Intermolecular Contact Distances: Quantifying Supramolecular SynthonsCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2008Parthasarathy Ganguly Prof. Abstract Crystal structures are viewed as being determined by ranges and constraints on interatomic contact distances between neighboring molecules. These distances are considered to arise from environment-dependent atomic sizes, that is, larger sizes for isotropic, van der Waals type contacts and smaller sizes for more-polar, possibly ionic contacts. Although the idea of different, or anisotropic, radii for atoms is not new, we developed a method of obtaining atomic sizes that is based on a theoretical framework. Using different atomic sizes for the same atom in different environments, we were able to rationalize some structural observations and anomalies. For example, benzene with the Pbca structure may be described in terms of two types of C,,,H interactions: a longer contact largely of the van der Waals type, and a shorter, structure-determining type (C,,,,,H,+), which we term "n-polar". Our approach is illustrated with three examples: 1),the equivalence in crystal packing of fluorobenzene, benzonitrile, pyridine N -oxide, and pyridine/HF 1:1 molecular complex, all of which take the not-so-common tetragonal P41212 space group and are practically isomorphous; 2),the similarity of the Pa3 acetylene and Pbca benzene crystal structures; and 3),the equivalence between an increase in pressure and an increase in the "n-polar" contacts in Pbca benzene; in other words, the equivalence between hydrostatic pressure and chemical pressure. In the context of crystal engineering, we describe a method whereby the topological information conveyed in a supramolecular synthon is recast in a more quantitative manner. A particular synthon, and in turn the crystal structure to which it leads, is viable within small ranges of distances of its constituent atoms, and these distances are determined by chemical factors. [source] Supramolecular Complexes Self-assembled by Copper(II) Carboxylate and Monohelical Pyridylamino LigandCHINESE JOURNAL OF CHEMISTRY, Issue 3 2006Li-Jun Zhou Abstract Two novel supramolecular complexes [Cu(bpapa)(dhbd)]·CH3OH (1) and [Cu(bpapa)(ma)]·ma (2) (bpapa=bis[6-(2-pyridylamino)pyrid-2-yl]amine, dhbd=2,3-dihydroxybutanedioate dianion, ma=, -methacrylate) were rationally designed, synthesized and characterized by single crystal X-ray diffraction, IR, electronic spectroscopy and thermogravimetric analyses. Complex 1 was the first oligo- , -pyridylamino complex based on hydroxypolycarboxylate and self-assembled into a 3D honeycomb configuration network with open channels and tubes containing 1D ladder-shaped double chains formed by hydrogen bonds and aromatic ,-, stacking interactions. Complex 2 constructed a 2D supramolecular network extended by 1D chains from dimeric supramolecular synthon through noncovalent supramolecular interactions. In the two complexes, the chelating monohelical ligand adopted all- anti configuration. Density functional theory calculations were applied to 1 and 2. [source] A Straightforward Synthesis of Isoxazoline-Based Carbocyclic Nucleosides from 1,3-Cyclohexadiene through Nitrosocarbonyl ChemistryEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 36 2007Paolo Quadrelli Abstract 3-Benzoyl-2-oxa-3-azabicyclo[2.2.2]oct-5-ene undergoes cycloaddition with benzonitrile oxide to afford a mixture of syn and anti regioisomeric cycloadducts. The anti cycloadducts were easily elaborated to stereodefined isoxazoline-based carbocyclic aminols that serve as synthons for the linear construction of purine nucleosides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] A New Class of Enehydroxylamino Ketones , (R)-2-(1-Hydroxy-4,4,5,5-tetraalkylimidazolidin-2-ylidene)ethanones: Synthesis and ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2004Vladimir A. Reznikov Abstract Three approaches to the synthesis of (R)-2-(1-hydroxy-4,4,5,5-tetraalkylimidazolidin-2-ylidene)ethanones 1 are described: (a) condensation of 1,2-bishydroxylamines with ,-ketoaldehyde synthons, (b) treatment of metallated 1-hydroxy-2-methyl-4,5-dihydroimidazoles with esters, and (c) 1,3-dipolar cycloaddition between 1-hydroxy-4,5-dihydroimidazole-3-oxide and DMAD. The reactivity of 1 with electrophiles has been studied. The exocyclic methylene (enamine) carbon atom is shown to be the major site of electrophilic attack. Synthesized chloro-substituted 1-hydroxy-2-acetylideneimidazolidines react with sodium cyanide to form the corresponding nitriles. Oxidation of these nitriles occurs with formation of persistent vinyl nitroxides, which are of interest as potential paramagnetic ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] New, Regioselective, One-Pot Synthesis of (all- E)-Retinoic Acid and Analogues from Enaminodiester SynthonsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2003Dominique Cartier Abstract A one-pot synthesis of (all- E)-retinoic acid and related compounds from new enamino diester synthons is described. The enamino diesters was produced nearly quantitatively from methyl propylidene- and isopropylidenemalonate and DMF,DMA. This easy process allowed retinoic acid to be produced in 1 d and appeared advantageous to current industrial syntheses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Novel N -(2,2-Dimethyl-2H -azirin-3-yl)- L -prolinates as Aib-Pro SynthonsHELVETICA CHIMICA ACTA, Issue 9 2006Simon Stamm Abstract The syntheses of phenacyl N -(2,2-dimethyl-2H -azirin-3-yl)- L -prolinate and allyl N -(2,2-dimethyl-2H -azirin-3-yl)- L -prolinate are reported. Reactions of these 2H -azirin-3-amine derivatives with Z-protected amino acids have shown them to be suitable synthons for the Aib-Pro unit in peptide synthesis. After incorporation into the peptide by means of the ,azirine/oxazolone method', the C-termini of the resulting peptides were deprotected selectively with Zn in AcOH or by a mild Pd0 -promoted procedure, respectively. [source] | ||||||||||||||||||||||||||||