13C NMR spectra of 7-substituted 8-mercaptoquinolines

The¹³C NMR spectra of 7-substituted [7-CH₃, 2,7-(CH₃)₂, 7-Cl, 7-Br, and 7-SCH₃] 8-mercaptoquinolines and 8-methylmercaptoquinolines were examined. It is shown that the changes in the¹³C chemical shifts of the quinoline ring in the spectra of 7-substituted 8-mercaptoquinolines are in good agreement with the additive contribution of the increments of the substituents, i.e., their conjugation with the ring is not disrupted. The conjugation of the SCH₃ group with the quinoline ring in 7-substituted 8-methylmercaptoquinolines is disrupted as a consequence of steric hindrance, and this leads to a decrease in the increments of this group. The data obtained are compared with the results of a calculation within the CNDO/2 approximation. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 801–805, June, 1980.     

Occurrence of the Unusual 2C5 (1C4) Chair Conformation in Two Carbohydrates and the Reverse Anomeric Effect. X-Ray Structures of 3,4,5,7-Tetra-O-Acetyl-2,6-Anhydro-D-Glycero-D-Ido-Heptonamide (1) and 3,4,5,7-Tetra-O-Acetyl-2,6-Anhydro-D-Glycero-L-Gluco-Heptonamide (2)

Abstract

The title compounds 1 and 2 (both C₁₅O₁₅NH₂₁) crystallized in the monoclinic space group P2₁ (Z = 2) with a=8.864(1), b=8.346(1), c =13.569(1)Å, β =114.12(1), V=918.1(2)A3, D(calc) = 1.358 g/cc for compound 1, and a=15–045(1), b=8.106(1), c=7.491(1)Å, β =97.23(1)°, V=906.4(3)Å3 D(calc)= 1.375 g/cc, for compound 2. The structures were solved by direct methods and refined by the full-matrix least squares technique to R indices of 0.010 and 0.046, respectively. Both compounds are in the α ? D configuration and adopt the unusual ²C₅, (¹C₄) chair conformation with the carbamoyl groups on the anomeric carbon atoms equatorially oriented. In this conformation the orientations of the substituents are 2e, 3a, 4a, 5a and 6a in 1 and 2e, 3a, 4a, 5e and 6a in 2 which leads to unfavorable 1,3-diaxial interactions. The “reverse anomeric effect” which induces the ²c₅ chair conformation in these compounds, may have its origin in the unfavorable steric interactions found in the ⁵c₂ (⁴C₁) conformation where the carbamoyl group is axially oriented. Furthermore, the ²C₅ conformation is stabilized by the N-H … O intramolecular hydrogen bond between the carbamoyl nitrogen atom and the pyranosyl ring oxygen atom. Semi-empirical energy calculations reveal that the rotational freedom of the carbamoyl group is greater for the equatorial orientation (²C₅) than for the axial orientation (⁵C₂).     

DFT study of 1-, 4-, and 5-substituted 2-oxo-1,2,3,4-tetrahydropyrimidines: substituent steric and electronic effects,and ring flipping

Steric and the electronic effects caused by the substituents in the 1-, 4-, and 5-positions of substituted 2-oxo-1,2,3,4-tetrahydropyrimidines were investigated using density functional theory at the B3LYP/6-31++G(d,p) level. Results of this study show that the heterocyclic ring adopts a pseudo-boat conformation, in which the C₄ and N₁ atoms are deviated from ring planarity. The C₄-substituent occupies a pseudo-axial position and the space orientation of the substituent depends on the type and position of the additional substituent in this aryl group. The heights of the C₄ and N₁ atoms from the boat plane and the orientation of 5-CO moiety toward the heterocyclic ring depend on the electronic and steric effects of the substituents in the various positions. Ring flip calculations for 4-phenyl substituent explain the extreme steric effect caused by the substituent in the 1-position. These calculations indicate the more favored pseudo-axial orientation of the phenyl group over the equatorial orientation.     

Product distributions in the addition of the hydride ion to cyclopentadienyliron complexes of substituted benzenes

Fifteen [C₆H₅(X)FeCp]⁺ cations with substituents X having different electron-donating or electron-withdrawing effects were treated with NaBH₄ in glyme or THF. The relative distributions of products from o-, m-, p- and ipso-additions of the hydride ion to the arene ring were determined by high resolution ¹H NMR. For the η⁶-N,N-dimethylaniline-η⁵-cyclopentadienyliron cation with the most electron-donating of the substituents studied, only m- and p-hydride addition products were obtained, while in the reaction with the η⁶-nitrobenzene-η⁵-cyclopentadienyliron cation, which contained the most electron-withdrawing of the substituents investigated, only the o-addition product was formed. For the other 13 cations, with X  C₆H₅O, CH₃O, p-CH₃C₆H₄S, C₆H₅CH₂, (CH₃)₃C, CH₃, CH₃CH₂, C₆H₅, Cl, COOCH₃, C₆H₅CO, CN and p-CH₃C₆H₄SO₂, o-, m- and p-hydride addition products were obtained in all cases, with a few instances also giving very minor amounts of ipso-adducts. The relative product distributions observed were interpreted by suggesting that while electronic effects played a major role, steric factors and free valency effects favoring o-addition as suggested by MO calculations [5] could also exert their influence in giving rise to the overall results.     

Optically active transition-metal compounds: XXII. Stereochemistry and crystal structure determination of (η5-C5H5)CoI(NC4H3C(R)=N(S)-CH(CH3)(C6H5)) (R = H,CH3)

The crystal structures and absolute configurations of (η⁵-C₅H₅)-CoI(NC₄H₃-C(R)=N(S)-CH(CH₃)(C₆H₅)) (R = H, compound I; R = CH₃, compound II) have been determined by single crystal X-ray diffraction. Crystals of compound I are orthorhombic, with a 11.084(6), b 12.107(6) and c 13.121(7) Å, space group ^P2₁2₁2₁ and d (calcd, Z = 4) 1.69 g cm^?3 The structure was solved by the Patterson technique and refined with use of full matrix least-squares methods to R(F) = 0.031 and R_w(F) = 0.028. Compound II is nearly isomorphous and isostructural; a 11.246(6), b 11.923(6) and c 13.370(7) Å, d(calc., Z = 4) 1.71 g cm^?3 and was refined to the final agreement factors of R(F) = 0.044 and R_w(F) = 0.035. The Co atom has a distorted tetrahedral coordination, with Co-I 2.595(2) for I and 2.607(2) Å for II; Co-(η⁵-C₅H₅ ring centroid) 1.681(4) and 1.703(5) Å; Co-N(pyrrole) 1.905(9) and 1.885(9) Å; Co-N(imine) 1.971(8) and 2.003(9) Å, all the parameters being well within values found in the literature. The configuration around the chiral carbon of the phenylethylamine is S for both compounds, whereas the configuration around the metal is R in I and S in II. The different metal configurations in I and II have their origin in the two different substituents (R = H, CH₃) at the imine carbon atoms of the chelate ring, which induce completely different conformations of the (S)-CH(CH₃)(C₆H₅) moiety in the two complexes. For both compounds the thermodynamically less stable isomer is enriched upon crystallization. Also, for compound I the solution and solid state conformations are almost opposite to each other, the conformation in the solid reflecting intramolecular interactions (phenyl/C₅H₅ attraction).     

Atranes. II. Dipole moments and structure of silatranes

Possible steric configurations of 1-organyl- and 1-organoxysilatranes,, are considered. The dipole moments of six compounds of this type (X=CH₃, (CH₃)₂CH, CH₂=CH, C₆H₅, C₂H₅O, C₆H₅O) have been found experimentally to be extremely high, 5.3–7.1 D. They conclusively show that the silatranes contain a semipolar transannular coordinate bond SiN between the negatively charged 5 -covalent silicon atom in the middle of the planar SiO₃ group and the tetrahederal onium nitrogen atom.Part I, see [1].     

Stereochemistry of nitrogen heterocycles. 69. 13C NMR spectra of stereoisomeric 10-methyl-5-oxygen-substituted trans-decahydroquinolines

The ¹³C NMR spectra of 5-keto- and 5a- and 5e-hydroxy-10-methyl- and 1,10-dimethyltrans-decahydroquinolines have been recorded and interpreted. The increments of the oxo and hydroxy groups in the 10-methyldecahydroquinoline and the isostructural 10-methyldecaline systems were compared. The difference between the increments of azacyclic and the carbocyclic systems appears- at the -positions relative to the electronegative substituents (C₍₇₎ and C₍₉₎) and at the antiperiplanar -positions relative to nitrogen (C₍₅₎ and C₍₇₎). The increments of the oxo and the equatorial hydroxy groups in the aza ring are more shielded than in the carbon ring (at C₍₇₎, 2 ppm; at C_(g), 1 ppm), while the increments of the axial hydroxy group are more deshielded (at C₍₅₎, 1.5–2.0 ppm; at C₍₉₎, 1.0–1.5 ppm). The more the respective carbon atoms of the heterocycle are hydrogenated, the stronger are the deshielding -effect and the shielding -effect of the methyl group on nitrogen.For Communication 68, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 60–65, January, 1990.     

Crystal and molecular structure of (η5-trimethylsilylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt

The structure of (η⁵-trimethylsilylcyclopentadienyl)(η⁴-tetraphenylcyclobutadiene)cobalt, ((CH₃)₃SiC₅H₄)Co((C₆H₅)₄C₄), has been determined by single crystal X-ray diffraction techniques using three-dimensional data collected on an automatic diffractometer. The crystals are monoclinic, space group P2₁/c, with lattice parameters a 11.551(1), b 16.352(6), c 18.324(2) », β 122.85(1)° with four molecules in the unit cell. The structure consists of discrete molecules in which a cobalt atom is sandwiched between the η⁵-cyclopentadienyl (Cp) and the η⁴-cyclobutadience (Cb) ligands bonded to the metal in the hapto mode. The perpendicular distances Co?(Cp) and Co?(Cb) of 1.688 and 1.699 », respectively, as well as the dihedral angle of 6.9° between the two rings and the distortions of their side groups, indicate steric interactions within the molecule. The Cb ring is planar within 0.015 » and has a rectangular shape with edges of 1.480(5) and 1.463(3) ». The Cp ring, which is planar to within 0.005 », appears to be highly distorted by the trimethylsilyl group, which induces a lengthening of the C—C distances involving the substituted carbon atom (1.440(7) ») and a narrowing of the corresponding bond angle (105.3(2)°).     

Structures and photochromic properties of substituted spiroindolinonaphthoxazines

Six indolinospironaphthoxazines were studied by X-ray diffraction analysis. It was demonstrated that the electronic nature of the substituents in the naphthoxazine and indoline fragments has no substantial effect on the C_spiro−O and C_spiro−N bond lengths. Photocolorability of the compounds under study depends only slightly on the abovementioned bond lengths and correlates mainly with the energy of steric strain of the oxazine ring. The stability of the open forms of spiroindolinonaphthoxazines that formed upon photoirradiation is determined to a large extent by the electronic and steric nature of the substituents. The exception is the compound that contains the NO₂ group in the indoline fragment. In the last-mentioned case, the cleavage of the ring occurs through a substantially different pathway. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1121–1128, June, 1998.     

Structural Organization of Symmetrical Dialkylthiuram Disulfides and Their Cyclic Analogs: X-Ray Diffraction and CP/MAS (13C, 15N) NMR Studies

High-resolution ¹³C and ¹⁵N solid-state NMR spectra were recorded for seven crystalline tetraalkyl-thiuram disulfides and their cyclic analogs of the general formula [R₂NC(S)S]₂ (where R = CH₃, C₂H₅, C₃H₇, and i-C₃H₇ or R₂ = (CH₂)₅, (CH₂)₆, and (CH₂)₄O). The ¹⁵N and ¹³C NMR resonances were assigned to the particular atoms in the compounds studied. Different isotropic ¹⁵N chemical shifts for both dialkyldithiocarbamato groups were interpreted while considering the inductive effects of the alkyl substituents combined with the mesomeric effect of the dithiocarbamato group. X-ray diffraction data were used to refine the molecular structure of bis(cyclohexamethylene)thiuram disulfide and to quantitatively characterize the conformations of the seven-membered N(CH₂)₆ heterocycles.     

13C n.m.r. studies of organosilanes: II—substituent chemical shift parameters for alkoxysilanes

The ¹³C n.m.r. spectra of forty alkoxysilanes of the general type X_nSi(OR)_4–n (X = CH₃, C₆H₅, H; R = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, s-C₄H₉, n-C₅H₁₁, CH(CH₃)(C₆H₅), C₆H₅) have been recorded and assigned. The chemical shifts of the α-carbon resonances of the alkoxy groups are shown to depend on both the nature of the alkoxy group and the number and type of substituents on the silicon. Regression analyses of the data give empirical substituent chemical shift (SCS) parameters for the silyl substituents. The β-carbon resonances are shown to be dependent on the presence of the silyl group, but not the specific silyl substituents.     

Aminoazoles in Heterocycles Synthesis: II. Trifluoromethyl-containing Diketones in the Synthesis of Pyrazolo[1,5-a]pyrimidines

A regioselective synthesis was carried out of 7-trifluoromethylpyrazolo[1,5-a]pyrimidines by reaction of 3(5)aminopyrazoles with 1,3-diketones containing CF₃ group. The characteristic chemical shifts were established for C⁵ and C⁷ atoms of the pyrimidine ring and of substituents thereof in the ¹H, ¹³C, and ¹⁹F NMR spectra of pyrazolo[1,5-a]pyrimidines.     

Unterschiedliche Cyclisierungsmechanismen von Aminofluorsilanen

Different Mechanisms of the Cyclisation of Aminofluorosilanes The reaction of aminofluorosilanes of the type RR′SiFNHR″ (R = H, F, CH₃, C₂H₃, C₆H₅, C(CH₃)₃; R′ = C(CH₃)₃, NiC₃H₇Si(CH₃)₃, NC(CH₃)₃Si(CH₃)₃, N[Si(CH₃)₃]₂; R″ = iC₃H₇, C(CH₃)₃, C₆H₅) with butyllithium depends on the steric influence of the ligands. With increasing size of the ligands the reaction takes its pathway from the substitution under LiF elimination via dimerisation with additional elimination of butan to the C? H cleavage and cyclisation via a methylen group. A further increase of the size of the substituted groups leads through the intermediate formation of a silicenium-ylid to ring closure reactions. These occure by migration of a methanid ion leading to intermolecular nucleophilic substitution. The isolated acyclic and heterocyclic compounds are described and the mass and ¹H-n.m.r. spectra are reported.     

Replacement of Imine Fragment in the Ring of 2,6-Disubstituted 1,4,3,5-Octathiadiazine-4,4-dioxides in Reaction with Cyano-containing Compounds

Reactions of 2,6-disubstituted 1,4,3,5-octathiadiazine-4,4-dioxides with cyano-containing compounds (nitriles, thiocyanates, N,N-disubstituted cyanamides) proceeding with replacement of imine fragment in dioxide by corresponding fragment of cyanide were investigated. The limits of the reaction were revealed determined by electronic effects of substituents R¹ and R² in dioxide and R³ in cyanide. Transimination occurred in dioxides with strong electron-withdrawing substituents R¹ (CCl₃, CBr₃, C₆F₅) and weak acceptor or donor substituents R²(4-NO₂C₆H₄, 4-ClC₆H₄, CH₃) under the action of compounds R³CN with cyano groups of relatively high nucleophilicity (R³ = 4-ClC₆H₄, C₆H₅, (CH₃)₂CHS, piperidino, morpholino, diethylamino), on the one hand, and with strong electron-withdrawing substituents R³ (CCl₃) on the other hand.     

Synthesis of potential antimalarials

A series of quinoline derivatives containing a 2-thienyl ring in the 2-position and CO₂H, CH₂OH, CHO, CH(OH)CN, CH(OH)CO₂H, CO₂C₂H₅, COCH[N(C₂H₅)₂]CO₂C₂H₅, COCH₂N(C₂H₅)₂, COCH₃, substituents in the 4-position was synthesized. Both intermediate and target compounds were tested for antimalarial activity. A second series with a 5-bromo-2-thienyl group in the 2-position and CHOHCH₂N(C₂H₅)₂, CHOHCH₂N(CH₂)₆, and CHOHCH₂N(CH₂C₆H₅)₂ substituents in the 4-position was also prepared, it was found that, although these quinoline methanols were moderately active antimalarials, they exhibited a high degree of phototoxicity. A third series of compounds with 2-alkyl substituents (methyl, t-butyl) was also synthesized, and these were found to combine a modest degree of antimalarial activity with low phototoxicity. Several novel synthetic routes to the above compounds were developed and are detailed.     

A 1,1‐Carboboration Route to Bora‐Nazarov Systems

Hydroboration of the conjugated enynes 1 a and 1 b with Piers’ borane [HB(C₆F₅)₂] gave the respective dienylboranes trans‐ 2 c and trans‐ 2 d . Their photolysis resulted in the formation of the dihydroborole products 3 c and 3 d . Both were converted to their pyridine adducts 5 c and 5 d , respectively. Compounds 3 c and 5 c,d were characterized by X‐ray diffraction. The reaction of the bis(enynyl)boranes 6 a and 6 b with B(C₆F₅)₃ resulted in the formation of the dihydroboroles 7 a and 7 b , respectively. This reaction is thought to proceed by 1,1‐carboboration of one of the enynyl substituents at boron to generate the dienylborane intermediates 8 a / 8 b , followed by thermally induced bora‐Nazarov ring‐closure and subsequent stabilizing 1,2‐pentafluorophenyl group migration from boron to carbon. Compound 7 a was characterized by X‐ray diffraction and solid‐state ¹¹B NMR spectroscopy.     

NMR study of (C6H5)3-nPXn (X = Cl,Br, I; n = 0-3) and (C6H6)3-n PXnCr(CO)5 compounds

The ³¹P chemical shift of the (C₆H₅)_3-nPX_n ligands (X = Cl, Br, I; n = 0–3) is dominated by the electronegativity of the substituents. π bonding is only important for derivatives with three strongly electronegative substituents. The ³¹P chemical shift of the corresponding complexes (C₆H₅)_3-nPX_nCr(CO)₅ is governed by the simultaneous effects of the electronegativity, steric hindrance and π bonding. The resonance parameter, δ', indicates an increasing (p_ring → d_p)π and (d_cr→ d_p)π electron delocalization with halogen substitution.     

Tri(1-cyclohepta-2,4,6-trienyl)phosphan,P(C7H7)3 und Tetra(1-cyclohepta-2,4,6-trienyl)phosphonium-tetrafluoroborat, [P(C7H7)4]BF4

Tri(1-cyclohepta-2,4,6-trienyl)phosphane, P(C₇H₇)₃, and Tetra(1-cyclohepta-2,4,6-trienyl)phosphonium Tetrafluoroborate, [P(C₇H₇)₄]BF₄ The reaction of tris(trimethylsilyl)phosphane, P(SiMe₃)₃, with tropylium bromide, C₇H₇⁺Br^?, in polar solvents such as dichloromethane or tetrahydrofuran gives P(C₇H₇)₃ ( 1 ) and [P(C₇H₇)₄]Br ( 2a ). According to the X-ray crystallographic structure determinations, all 1-cyclohepta-2,4,6-trienyl substituents are present in the boat conformation in both P(C₇H₇)₃ ( 1 ) and the phosphonium salt, [P(C₇H₇)₄]BF₄ ( 2b ). The boat-shaped C₇H₇ rings are significantly more flattened if the phosphorus occupies the axial rather than the equatorial position at the ring substituent. Addition of a chalcogen to the lone pair at the central phosphorus atom of 1 leads to the chalcogena-phosphoranes EP(C₇H₇)₃ (E = O ( 3a ), S ( 3b ), Se ( 3c )). The new 1-cyclohepta-2,4,6-trienyl-phosphorus compounds 1, 2 b and 3a–c were characterized by their ¹H, ¹³C, and ³¹P NMR spectra in C₆D₆ solution.     

A Dimer of Hydrogen Cyanide Stabilized by a Lewis Acid

A highly labile dimer of hydrogen cyanide, HCN???HCN, was extracted from liquid HCN by adduct formation with the bulky Lewis acid B(C₆F₅)₃, affording HCN???HCN?B(C₆F₅)₃, which was fully characterized. The influence of the solvent (HCN, CH₂Cl₂, and aromatic hydrocarbons) on the crystallization process was studied, revealing dimer formation when using HCN or CH₂Cl₂ as solvent, whereas aromatic hydrocarbons led to the formation of monomeric arene??HCN?B(C₆F₅)₃ adducts, additionally stabilized by η⁶‐coordination of the aromatic ring system similar to well‐known half‐sandwich complexes.     

Adducts of zinc and copper(II) dialkyldithiocarbamate complexes with dialkylamines: Synthesis,EPR, and <Superscript>13</Superscript>C and <Superscript>15</Superscript>N CP/MAS NMR

Crystalline adducts of zinc and copper(II) dithiocarbamate (Dtc) complexes with dialkylamines [M(NHR′₂)(S₂CNR₂)₂] (M = Zn, ⁶³Cu, ⁶⁵Cu; R = CH₃, C₂H₅, or R₂ = (CH₂)₄O; R′ = C₂H₅, C₃H₇) have been preparatively isolated. The structures and spectral properties of the adducts have been studied by EPR and ¹³C and ¹⁵N MAS NMR. Chemisorption of bases on powders of dinuclear dithiocarbamates leads to their dissociation into monomeric adducts. Computer simulation demonstrates that the experimental EPR spectra of isotope-substituted copper(II) adducts have an individual character. The geometry of the copper polyhedra is intermediate between a trigonal bipyramid (TBP) and a tetragonal pyramid (TP). The TBP and TP contributions have been quantified based on EPR data. ¹³C and ¹⁵N MAS NMR data show that the Dtc ligands incorporated into the zinc adduct molecule are structurally nonequivalent. The dependence of the isotropic ¹⁵N chemical shifts of the Dtc groups on the alkyl substituents at the nitrogen atom is interpreted based on the concept of joint manifestation of the (+)inductive effect of the alkyl substituents and the mesomeric effect of the Dtc groups.