Phosphonium keto ylides react with metal salts to form not only ylide complexes but also phosphonium salts (Antipin & Struchkov, 1984; Baby Mariyatra et al., 2002) and phospho- nium metalates (Albanese et al., 1989; Bart et al., 1982). The action of trimethyltin chloride on (benzoylmethylene)tri- phenylphosphorane led to the ®rst O-coordinated ketoylide complex (Buckel et al., 1972). The reaction of SnI 4 with the
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Propiophenone is a colourless liquid that has been incorpor- ated as a guest into inclusion compounds (Scott, 1997; Gdaniec & Polonski, 1998; Nakano et al., 2001). The 4-chloro deriva- tive, (I), has a low melting point (307±310 K) and has also been subjected to an X-ray crystallographic examination as a guest molecule in an inclusion compound (Weisinger-Lewin et al., 1987). The low melting point suggests that the crystal packing forces are easily broken, and these interactions have been characterized in this investigation.
The asymmetric unit of (I) contains two crystallographically independent molecules (Fig. 1). The corresponding bond lengths of these two molecules agree with each other (Table 1). The C14—C15 and C33—C34 bond distances agree with the corresponding distance of 1.5628 (19) A ˚ reported for 8,9- dihydro-1,6-dimethylphenanthro[1,2-b]furan-10,11-dione (Qin et al., 2005). In one of the molecules, the cyclohexene ring A is disordered. In both molecules, ring A adopts a half- chair conformation and the five-membered ring D adopts a distorted half-chair conformation. Intramolecular C—H O hydrogen bonds are observed in the molecular structure (Table 2), but no intermolecular hydrogen bonding is observed in the crystal structure.
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Molecular packing in (I): (a) view of two-dimensional supramolecular array sustained by hydroxy-O—H O(hydroxy) and hydroxy-O– H N(pyridyl) hydrogen bonding with all but the acidic H atoms removed and (b) a view of the unit-cell contents in projection down the c axis, with the non-coordinating 4,4 0 -bipyridine molecules in one channel
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C2/c with eight molecules in the unit cell. Excluding for the ethyl substituent, the molecule of I adopts a nearly coplanar conformation (r.m.s. deviations is 0.058 A ˚ ), which is supported by the intramolecular C—H O hydrogen- bonding interaction between the two ring systems [C O = 2.859 (3) A ˚ ]. In the crystal, the molecules form dimeric associates via two bifurcated C—H O hydrogen-bonding interactions between an ene hydrogen atom and a carbonyl functional group of an adjacent molecule [C O = 3.133 (3) A ˚ ] and vice versa. The crystal structure is further stabilized by a three-dimensional network of weak hydrogen bonds between one molecule and six adjacent molecules as well as offset – stacking. The combination of the quinoxaline 2(1H)-one moiety with the dithiocarbonate moiety extends the aromaticity of the quinoxaline scaffold towards the substituent as well as influencing the -system of the quinoxaline. The title compound is the direct precursor for a dithiolene ligand mimicking the natural cofactor ligand molybdopterin.
Our synthetic and spectroscopic studies of peptides have shown that, in the solid state, a critical size is needed to fold helices. For Leu- and Ala-based sequences, at least 10±14 residues are required to form a helical structure (Katakai 1977a,b, 1979; Katakai & Nakayama, 1977). Sequences shorter than this critical length invariably exist in the -sheet conformation. To examine the sheet structure of (I) at a molecular level, the crystal structure of (I) has been deter- mined.
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The design of organic polar crystals for quadratic non-linear optical (NLO) applications is supported by the observation that organic molecules containing π-electron systems asymmetrized by electron-donor and -acceptor groups are highly polarizable entities in which problems of transparency and crystal growth may arise from their molecular crystal packing (Pecaut & Bagieu-Beucher, 1993). It is known that nitrophenols act not only as π-acceptors to form various π-stacking complexes with other aromatic molecules, but also as acidic ligands to form salts through specific electrostatic or hydrogen-bonding interactions (In et al., 1997). The bonding of electron-donor acceptor complexes depends strongly on the nature of the partners. The linkage could involve not only electrostatic interactions, but also the formation of molecular complexes (Zadrenko et al., 1997). It has been reported that proton-transferred thermochromic complexes are formed between phenols and amines in apolar solvents at low temperature if an appropriate hydrogen-bonding network between phenols and amines is present to stabilize it (Mizutani et al., 1998). Pyridinium picrate has been reported in two crystalline phases and it appears in both phases as an internally linked hydrogen-bonded ion pair. These two phases are termed molecular crystals rather than salts, based on their structural arrangements (Botoshansky et al., 1994). A similar structural arrangement has also been reported for 4-dimethylaminopyridinium picrate (Vembu, Nallu, Garrison & Youngs, 2003). The reaction of 4-nitrophenol with 4-dimethylaminopyridine results in the formation of a new NLO material, the crystal structure of which has been reported at room temperature (Evans et al., 1998). Recently, we have reported the crystal structure of 4-dimethylaminopyridinium 4-nitrophenolate 4-nitrophenol (1/1/1) at 120 K (Vembu, Nallu, Spencer & Howard, 2003). The X-ray structure determination of the title compound, (I), has been undertaken to study the nature of the interaction between 4-dimethylaminopyridine and 2,4-dinitrophenol in the solid state. This study may serve as a forerunner for assessing the optical properties of (I).
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The wide range of applications involving hydrogen isotopes makes their installation an important and continuing challenge to synthetic chemists. Despite the apparent simplicity of the transformation, hydrogen isotope exchange requires a continually evolving preparative toolbox in order to satisfy the escalating regio-, chemo-, and stereoselectivity demands set by practicing isotope chemists. Indeed, we have deliberately avoided any ranking of the synthetic methods described herein, since it is the increasing breadth of methods that is, and will remain, most important in tackling the incalculable variation in the necessary HIE approaches required within different drug design projects, as part of selective labeling of substrates for mechanistic studies, and beyond. It is envisaged that these requirements will continue to drive developments in homogeneous, heterogeneous, and acid/base-catalysis in order to expand on the existing methods available for isotope incorporation. The widespread use of embedded deuterium and tritium units makes efforts towards the further development of these fundamental synthetic transformations increasingly valued. Moreover, and of even more widespread resonance for preparative chemistry, the evolving synthetic developments in late-stage hydrogen isotope exchange provides increasing data resources with which to understand the fundamental nature of various C–H functionalization methodologies. For selective labeling protocols, a key synthetic challenge for future developments will be to further consider directing group chemoselectivity and innate regioselectivity in increasingly complex drug-like architectures. Additionally, further escalation of catalyst activity and selectivity is required in order to expand beyond the established array of sp 2 functionalization methods
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A mixture of 3-aminocrotononitrile (2 mmol), isonicotinoyl hydra- zine (2 mmol) and sodium acetate trihydrate (2 mmol) in ethanol (50 ml) was heated under reflux for 2 h. The mixture was then cooled to ambient temperature and poured into water (50 ml) with vigorous stirring, which was continued for 20 min. The resulting solid product was collected by filtration and recrystallized from aqueous ethanol (97:3 v/v), yielding colourless crystals of compound (I) suitable for single-crystal X-ray diffraction (m.p. 540–541 K).
In a 10 ml one-necked flask, [8-(4-benzoyl)-2,7-dimethoxynaphthalen-1-yl](4-fluorophenyl)-methanone (1.0 mmol, 414 mg), phenol (1.5 mmol, 141 mg), potassium carbonate (2.5 mmol, 346 mg) and freshly distilled dimethylacetamide (2.5 ml) were stirred at 423 K for 6 h. This mixture was poured into 2M aqueous HCl (100 ml). The aqueous layer was extracted with ethyl acetate (20 ml × 3). The combined extracts were washed with water followed by washing with brine. The extracts thus obtained were dried over anhydrous MgSO 4 . The solvent was removed under reduced pressure to give a
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The asymmetric unit of the title compound is composed of two independent molecules (hereafter called A and B) depicted in Fig. 1 and 2, respectively, and a water molecule of hydration. The furyl and triazole rings in molecule A are substantially planar (maximum deviation 0.0586 (13) Å for atom N2), with the S1 atom 0.1980 (16) Å out of this plane; the mean-planes of the furyl and triazole form a dihedral angle of 5.63 (15)°. The corresponding furyl and triazole rings in molecule B are far from planar with atoms O2 and C17 deviating from the plane by 0.2571 (11) and -0.1633 (15) Å, respectively. The mean-planes of the five-membered rings in molecule B form an angle 17.66 (13)°. In both molecules, the benzyl rings are oriented at 80.72 (4) and 80.70 (4)°, from the planes formed by the ten atoms of the furyl and triazole rings in the molecules A and B, respectively. Bond distances and angles in the two molecules agree well with each other. Similar bond distances and bond angles have been reported in compounds closely related to the title compound, e.g., 4- chlorophenyl analogue (Öztürk et al., 2004), 4-methoxyphenyl analogue (Yıldırım et al., 2004) and 4-p-tolyl (Dege et al., 2004); in all these compounds, the mean-planes of the phenyl rings and those of the furyl and triazole rings lie close to right angles. The water molecule of hydration links three adjacent molecules of the title compound to form a cluster via intermolecular hydrogen bonds (Fig. 3, Table 1), forming a 10-membered ring of graph set R 3
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isotropic phases, respectively. The observed transition temperatures and enthalpies from the solid phase to the liquid crystalline phase are in good agreement with those reported Kato et al. (1990, 1993). Some unreported thermal anomalies, 373 (2) K for (I), 365 (1) and 369 (1) K for (II), and 358 (1) and 386 (1) K for (III), were also observed.
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and C—H N contacts. The supramolecular structure is mainly governed by C—H N hydrogen-bonded centrosymmetric dimers, C—H O and C—H S hydrogen bonds and S and – stacking interactions which, together, lead to the formation of a layered crystal packing. The intermolecular interactions were further evaluated through the molecular electrostatic potential map and Hirshfeld fingerprint analysis.
We have recently described the preparation of pyrazolo[3,4- b]pyridines from 5-aminopyrazoles in solution with different reactants (Low et al., 2002, and references therein), and we have reported the crystal structure of the fully aromatized 3- methyl-1,4-diphenyl-1H-pyrazolo[3,4-b]pyridine (Low et al., 2002). We report here an analogous structure, that of 3-tert- butyl-4-(4-nitrophenyl)-1-phenyl-1H-pyrazolo[3,4-b]pyridine, (I), obtained from the solvent-free reaction of the corres- ponding 5-aminopyrazole and the Mannich adduct - dimethylamino-4-nitropropiophenone hydrochloride, under microwave irradiation. The title compound, (I), was obtained along with the reduced 6-(4-nitrophenyl) analogue, (II); however, in pyridine solution under reflux, a similar reaction yielded regioselectively the isomeric 6-arylpyrazolo[3,4- b]pyridine (Quiroga et al., 1998).
The shortest C—H O contacts tend to be between the equatorial oxygen atoms, O1, and the equatorial hydrogen atoms labeled with the suffix B. These also come with C— H O angles that are closest to being linear, 148 to 160 . Presumably the difference between axial and equatorial H O contacts is mostly due to steric effects, the equatorial atoms being more accessible. The shorter contacts can undoubtedly be classified as true C—H O hydrogen bonds using, as a guide, the seminal study of weak hydrogen bonds by Desiraju & Steiner (1999). The remaining bonds are probably better described as mostly electrostatic in nature. However, as Desiraju & Steiner point out, there are no hard limits for determining what may, and may not, be a true hydrogen bond.
described in the previous section, but are further stabilized by hydrogen bonds across the non-coordinating dca anions (N51 and N55/56) and by hydrogen bonds involving N1 and N25 of the mono-dentate non-bridging dca ligand. In addition to the O—H N hydrogen bonds, C—H N hydrogen bonds are also present in the title structure between C—H groups of the tetraethylammonium cations and dicyanamide amide nitrogen atoms (Fig. 2). The hydrogen-bond lengths and angles are summarized in Table 1.
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HBPPY cations and the hydrogen maleate anions are connected through CÐH O interactions, forming close- packed zigzag layers in the bc plane (Table 2 and Fig. 2). Both the methylene H8A and H8B atoms are involved in the interionic CÐH O interactions (Fig. 3). Atom H8B forms a bifurcated hydrogen bond with O4 and O5 of the hydro- genmaleate ion at (1 ÿ x, ÿy, 1 ÿ z). A CÐH interaction
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The crystal structure of (I) is stabilized by weak CÐH O interactions. The range for the H O distances (Table 2) agrees with that found for weak CÐH O bonds (Desiraju & Steiner, 1999). The C4ÐH4 O1 interaction generates a ring of graph set S(5) (Etter, 1990; Bernstein et al., 1995). Another S(5) motif is formed by the C6ÐH6 O2 interaction. The C13ÐH13 O2 interaction generates an S(6) motif. The C6Ð H6 O2 and C13ÐH13 O2 interactions constitute a pair of bifurcated acceptor bonds. The C7ÐH7 O3 iii and C7Ð
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acrosome reaction (Spungin et al., 1992), development of immunoaffinity chromatography for the purification of human coagulation factor (Tharakan et al., 1992), chemical studies on viruses (Alford et al., 1991), development of technology for linking photosensitizer to model monoclonal antibody (Jiang et al., 1990) and chemical modification of sigma sub units of the E-coli RNA polymerase (Narayanan & Krakow, 1983). An X-ray study of the title compound, (I), was undertaken in order to determine its crystal and molecular structure owing to the biological importance of its analogues.
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Sulfonylbenzotriazole derivatives are versatile synthetic intermediates both as benzotriazolyl donors (Katritzky et al., 2001) and as sulfonyl donors (Katritzky et al. , 2004) because both have good leaving groups. The sulfonylbenzotriazoles can be readily prepared from benzotriazole and sulfonyl chlorides or from 1-chlorobenzotriazole and sulfonic acids. We report here the structure of 1-(4-methylphenylsulfonyl)-1H- 1,2,3-benzotriazole, (I), which was obtained adventitiously in 54% yield when the addition of benzotriazole to the double bond in (4S,5R,6R)-diphenylmethyl (E)-4,5,6,7-tetrahydroxy- 2-heptenoate was attempted in the presence of 4-toluene- sulfonic acid. The direct reaction between benzotriazole and 4-toluenesulfonic acid in ethanol under reflux did not give any product and addition of diphenylmethanol to such a mixture yielded only the reported 1-diphenylmethyl-benzotriazole (Ma¨rky et al., 1979), suggesting that transesterification, via a sulfonic ester, is required to produce the title compound in this way.