Volume 59, Issue 1

The low-temperature (LT) polymorph of tetramethyldiphosphine-bis(monoborane), Me 2 (H 3 B)PP( BH 3 )Me 2 , was obtained by crystallization from diethyl ether at 4 °C. It crystallizes in the monoclinic space group P2 1 /c, a = 6.464(1), b = 7.605(1), c = 11.867(2) Å , β = 119.99(1)° (at 153 K) with 2 molecules per unit cell. This implies that the individual molecules have crystallographic inversion symmetry and a strict anti arrangement with respect to the central B-P-P-B skeleton. At 87.6 °C (DTA) the LT polymorph transforms to the high-temperature (HT) modification which contains the anti and gauche conformers in a 1:2 ratio (P2 1 /c, Z = 6; H. L. Carrell, J. Donohue, Acta Crystallogr. B24, 699 (1968)). This strongly suggests that the gauche conformer is higher in energy and stabilized by the crystal packing of the HT modification. The P-P-B angle in the anti LT form (113.91(6)°) ascertains the value of the anti conformer in the HT form (114.4(6)°) which was found to be significantly different from the gauche conformer which centered around 110 °C.

The new ternary alkali pentelides A 11 M 6 (A = Rb, Cs; M = Sb/Bi) all contain non electron-precise isolated dumbbells statistically composed of Sb/Bi. Their phase ranges as determined from single crystal data were found to be on the Sb-rich side of the overall composition A 11 Sb 6−x Bix in the case of the Rb compound (i. e. Rb 11 Sb 5.4 Bi 0.6 : orthorhombic Immm, a = 766.7(3), b = 1052.2(3), c = 1732.7(6) pm, Z = 4, R1 = 0.0554), and on the Bi-rich side of the overall composition A 11 Sb 6−x Bix in the case of A = Cs (i.e. Cs 11 Sb 1.6 Bi 4.4 ). In the series of known alkaline earth compounds A 11 M 10 , containing pentelide dumbbells among isolated Zintl anions, a redetermination of the structure of Ba 11 Sb 10 (orthorhombic, Immm, a = 1265.3(2), b = 1316.1(3), c =1947.2(5) pm, Z = 4, R1 = 0.0724) shows, that it represents a distorted variant of the tetragonal Ho 11 Ge 10 structure type. This distortion is not only of crystallographic importance, as it results in a major change in the nature of the anions and their bonding, which is supported by DFT band-structure calculations. Likewise, the Zintl phase BaSb 2 (monoclinic, P2 1 /m, a = 1167.9(9), b = 438.1(5), c = 1257.1(9) pm, β = 100.53(2)°, Z = 6, R1 = 0.0648) crystallizes with a superstructure of the CaSb 2 -type previously reported.

As an exercise in crystal engineering, preparations and low-temperature X-ray structures are reported for three ionic solids of general formula BH + (MeSO 2 ) 2 N − , where BH + is 2,4,6- triaminopyrimidinium (compound 1, triclinic, space group P1, Z = 2), 2,6-diaminopyridinium (2, monoclinic, C2/c, Z = 8), or 2,4-diaminopyrimidin-6(1H)-on-3-ium (3, monoclinic, P2 1 /c, Z = 4). As a common feature, the onium cations in question exhibit a trifunctional hydrogen-bond donor sequence H-N-C-N(H)-C-N-H that is complementary to a W-shaped O-S-N-S-O fragment of the anion. Consequently, each structure displays a [DDD:AAA] three-point hydrogen-bond pattern formed by two lateral N-H···O bonds and a central N-H···N interaction. This grouping is integrated as a robust supramolecular synthon into two-dimensional (1, 2) or three-dimensional (3) hydrogen-bond networks, in which all good donors and all good acceptors are involved (excepting one S=O group in 2). In structure 1, the approximately planar cation-anion layers are perfect mosaics composed of 6-membered pyrimidine heterocycles and seven crystallographically independent types of 8-, 10-, 12- or 24-membered rings based upon hydrogen bonding. In contrast, the corresponding layers in structure 2 are marred by large 40-membered voids; in order to achieve dense packing, the imperfect layers adopt a strongly corrugated shape and interpenetrate to form twofold interwoven and nearly planar double-layers. Each structure features close C-H···O contacts consistent with weak hydrogen bonding; in the layer structures 1 and 2, some of these interactions serve as links between adjacent or interwoven layers.

Compared with the tertiary phosphane P(C 7 H 7 ) 3 (1), the amine N(C 7 H 7 ) 3 (2) possesses the structure of a flattened trigonal pyramid with a sum of CNC angles of 350.0° (cf. 300.2° (av.) in 1). The heteroatom (with the lone pair) is situated 27.0 pm above the C 3 basal plane in 2, but 86.4 pm in 1. The amines N(C 7 H 7 ) 3 (2), NH(C 7 H 7 ) 2 (2a) and N(Ph)(C 7 H 7 ) 2 (2b) react with tropylium tetrafluoroborate, [C 7 H 7 ]BF 4 , to give N-tropylidene-(1-cyclohepta-2,4,6-trienyl)-immonium tetrafluoroborates, [(C 7 H 6 )N(R)(C 7 H 7 )]BF 4 3 (R = H, from 2 and 2a), 4 (R = Ph, from 2b), which have been characterized by their IR and NMR ( 1 H, 13 C) spectra.

Single crystals of ScOH(CH 3 SO 3 ) 2 were obtained from a solution of Sc 2 (CO 3 ) 3 in methanesulfonic acid at pH 7. According to the X-ray single crystal structure determination, the compound crystallizes with the non-centrosymmetric orthorhombic space group Pmc2 1 (Z = 8, a = 743.92(8), b = 1497.7(3), c = 1540.1(2) pm, Rall = 0.0925) and contains the Sc 3+ ions in octahedral coordination of oxygen atoms which belong to two OH− and four CH3SO3 − ions. The linkage of the Sc 3+ ions leads to chains according to the formulation 1 ∞ [Sc(CH 3 SO 3 ) 4/2 (OH) 2/2 ] which are oriented along the [100] direction and connected via hydrogen bonds. The IR spectrum of the compound shows the typical bands of the CH 3 SO 3 − ion.

Singlet state structures of small, cyclic hydrocarbons which can result from the addition of molecular dicarbon (C 2 ) to ethyne (HC≡CH) or ethene (H 2 C=CH 2 ) have been calculated (B3LYP/6- 311+G(d,p) level of theory), and were found to contain carbene centres. Some structures of analogous boranes (replacement of the carbene centers by BH fragments) were also calculated. The computation of NMR parameters such as chemical shifts δ 13 C and δ 11 B, and coupling constants 1 J( 13 C, 1 H), 1 J( 11 B, 1 H), J( 13 C, 13 C) and J( 13 C, 11 B) shows that these data can be used for the discussion of the bonding situation. The presence of inverted carbene centers is clearly indicated by the increased 13 C nuclear magnetic shielding. Scalar 13 C- 13 C spin-spin coupling involving carbene centers are frequently dominated by spin-dipole and spin-orbital interactions.

The volume changes of solid iodine under pressure are discussed with respect to the packing density of the atoms and to valence. The packing density of solid iodine which is 0.805 under ambient pressure increases to 0.976 in monoatomic iodine-II, 0.993 in iodine-III, and 1 in fcc iodine-IV. Simultaneously, the valence increases from 1 in the free molecule to 1.78 in the crystal structure under ambient pressure, 2.72 - 2.81 in iodine-II, 2.86 - 2.96 in iodine-III, and 3 in fcc iodine-IV. The valence then remains constant up to about 180 GPa and rises moderately to 3.15 at the highest investigated pressure of 276 GPa. Parameters for calculating bond numbers, valences and atomic volumes of densely packed halogens, hydrogen, oxygen, and nitrogen are given.

Secondary interactions in the structures of [(etu) 2 Au] + Cl − .H 2 O (1), [(etu) 2 Au] + Cl − (2) and [(Me-etu) 2 Au] + Cl − (3) (etu = imidazolidine-2-thione) have been analysed. Within the cations, the torsion angle C-S...S-C is effectively the sole degree of freedom, and varies from almost eclipsed for 1 (−20°) via −79° for 2 to exactly 180° in 3. Both 1 and 2 form ten-membered rings in which the water molecule or the chloride ion respectively act as hydrogen bond acceptor to two NH donors of the cation. Further classical hydrogen bonds lead to the formation of double layer structures. Compound 3, in which the gold atom lies on an inversion centre and the chloride on a twofold axis, utilises its one N-H...Cl contact to form chains of hairpin bends, with Au...Cl contacts in the chain direction. Weak hydrogen bonds C-H...Cl and C-H...Au play at best a minor role in 1, but are more pronounced in 2 and 3.

Two new erythroxylane diterpenes, named givotin A (1) and givotin B (2) were isolated from the bark of Givotia madagascariensis. Their structures have been established as 3α,12α-dihydroxy- 4(19),15-erythroxyladiene (1) and 3α-hydroxy-4(19),15-erythroxyladiene (2), respectively, on the basis of one and two-dimensional NMR spectroscopic studies ( 1 H, 13 C, COSY, HMQC, HMBC, NOESY, NOE difference spectra) as well as on mass spectral analysis. In addition six known compounds (3 - 8) have been isolated and identified. Cleistanthol (3), spruceanol (4) and 1,2- dihydroheudelotinol (5) demonstrated significant antitumor activities against three tumor cell lines (HM02, Hep G2, MCF7).

To study the variation of oxidative strengths of N-chloro-arenesulphonamides with substitution in the benzene ring, six mono- and five di-substituted N-chloro-arenesulphonamides are employed as oxidants for studying the kinetics of oxidation of two neutral amino acids, L-leucine and Lisoleucine in aqueous acid medium. The N-chloro-arenesulphonamides studied are of the constitution: ArSO 2 NaNCl·H 2 O (where Ar = C 6 H 5 , 4-CH 3 C 6 H 4 , 4-C 2 H 5 C 6 H 4 , 4-FC 6 H 4 , 4-ClC 6 H 4 , 4-BrC 6 H 4 , 2,3-(CH 3 ) 2 C 6 H 3 , 2,4-(CH 3 ) 2 C 6 H 3 , 2-CH 3 -4-ClC 6 H 3 , 2,4-Cl 2 C 6 H 3 , and 3,4-Cl 2 C 6 H 3 ). The reactions show second order kinetics in [oxidant], fractional order in [amino acid] and inverse dependence on [H + ]. Addition of the reduced product of the oxidants or variation in ionic strength of the medium has no significant effect on the rates of oxidations. A two-pathway mechanism is considered to explain the experimental results. Effective oxidizing species of the oxidants is Cl + in different forms. Therefore the oxidising strengths of N-chloro-arenesulphonamides depend on the ease with which Cl + is released from them. The study reveals that the introduction of substituent in the benzene ring of the oxidant affects both the kinetic and thermodynamic data for the oxidations The electron releasing groups such as CH 3 generally inhibit the rates, while electron-withdrawing groups such as Cl enhance this ability, as the electron withdrawing groups ease the release of Cl + from the reagents and hence increase the oxidising strengths. The on Ea and logA and validity of the Hammett and isokinetic relationships for the oxidations are also analysed.

The enone unit of chalcones is a synthetically valuable substructure for the formation of heterocycles. Whereas propoxy groups as solubilizing side chains on the phenyl groups do not much affect the generation of pyrazole and pyridine rings, they reduce significantly the yield of the diazepine ring system 4. We attribute this effect to the large twist angles between the ring planes, which are demonstrated by a crystal structure analysis.

A novel class of (difluorocyclopropyl)propyl nucleoside analogues containing a propyl spacer between the cyclopropane moiety and the heterocycle has been prepared in an easy sequence.

Besides the known compounds 2,4,6-trihydroxyacetophenone 4-O-β -D-glucopyranoside and syringaresinol 4’-O-β -D-glucopyranoside, the novel sesquiterpenoid 1,2-dehydro-3-oxocostic acid β - D-glucopyranoside ester was isolated from Leontodon tuberosus L. and its structure established by mass spectrometry and 1D- and 2D-NMR spectroscopy. Additionally, a number of fatty and phenolic acids was identified in the crude methanolic extract by HPLC-DAD and HPLC-MS. The chemosystematic impact of the new sesquiterpenoid is discussed briefly.

The first X-ray structure analysis of authentic, not derivatized (racemic) trans-isoshinanolone, a wide-spread acetogenic tetralone, is described. In the crystal, two slightly different conformers are found, along with the corresponding enantiomers. The ‘homomeric’ conformers differ by their H-bonding interactions with the respective neighboring molecules. Rows of a single enantiomeric species, but with the two conformers linked ‘head-to-head’, ‘tail-to-tail’, are surrounded by four analogous rows of the corresponding enantiomers. Apparently the interactions between these heterochiral rows are the reason for the enhanced crystallization tendency of the racemate as compared to that of enantiomerically pure isoshinanolone. The structures in the crystal are compared with those calculated (gas phase) and with the structure in solution.

2-Benzylidene-1-oxo-1,2,3,4-tetrahydrocarbazoles (1a - e) obtained from the corresponding 1- oxo-1,2,3,4-tetrahydrocarbazoles on reaction with malononitrile in dry benzene with sodium hydride afforded 3-cyano-5,6-dihydro-2-ethoxy-4-phenyl-pyrido[2,3-a]carbazoles (2a - e) in good yields. A plausible mechanism for the formation of the title compound has been proposed and all the compounds were characterised by IR, NMR, mass spectral methods and elemental analysis.

Remote substituent effects on the regioselectivity and stereoselectivity in the boron trifluoride mediated addition of nucleophiles (iodide and bromide) to endo- and exo-2-substituted norbornene derivatives have been investigated. The main products of the reactions resulted from the regioselective addition of nucleophiles to the double bond of norbornene derivatives. Products resulting from the Wagner-Meerwein type rearrangement were also isolated in considerable amounts. All of the reactions gave the addition products in reasonably good yields with high regioselectivity. The endo/exo selectivity, on the other hand, changed depending on the nucleophile and the substrate.

Two novel sesquiterpenoids of tricyclo[5.4.0.0 2.5 ]undecane skeleton, fascicularones C (5) and D (6) have been isolated from liquid culture of a poisonous mushroom, Naematoloma fasciculare. Their structures were elucidated on the basis of spectroscopic methods. Compounds 5 and 6 promoted radicle elongation of lettuce seedling.

The new triterpenoid saponin 3-O-[α-L-rhamnopyranosyl-(1→2)-β -D-xylopyranosyl-(1→2)- β -D-glucuronopyranosyl]-3β ,22α-dihydroxyolean-13-en-11-one has been isolated from Ononis spinosa. The new flavonoid glycoside 3-O-[2-O-(E)-p-coumaroyl-β -D-galactopyranosyl]-7-O-β - D-glucopyranosylkaempferol and the new pterocarpan glucoside 3,4-di-O-β -D-glucopyranosyl-4- hydroxymedicarpin have been obtained from Ononis vaginalis. The structures were determined primarily by NMR spectroscopy. The assignment of NMR signals was performed by means of 1 H- 1 H COSY, ROESY, TOCSY, HMQC HMQC-COSY and HMBC experiments.