Pteridine. Teil XCIV. Synthese und Eigenschaften von 5,6-Dihydro-6-(1,2,3-trihydroxypropyl)pteridinen: Kovalente intramolekulare Addukte

Pteridines: Synthesis and Characteristics of 5,6-Dihydro-6-(1,2,3-trihydroxypropyl)pteridines: Covalent Intramolecular Adducts Various 5,6-diaminopyrimidines ( 1, 15, 24, 33 ) were condensed with the phenylhydrazones of L -( 2 ) and D -arabinose ( 3 ) in acidic medium under N₂ to give formal 5,6-dihydro-6-(1,2,3-trihydroxypropyl)pteridines (see, e.g., 4 and 5 ), the latter turned out to exist preferentially as intramolecular adducts, the hexahydropyrano-[3,2-g]pteridines 6, 7, 16, 17, 25, 26 , and 34 , formed subsequently by addition of the terminal OH group of the side-chain to the C(7)?N(8) bond of the pteridine moiety. Spectroscopically, the isomeric hexahydrofuro-[3,2-g]pteridines 10,11,18,19 , and 35 were also detected as minor components in the equilibrium mixtures. In the 4-amino-2-(methylthio)pteridine series, crystallization of 6 and 7 led to the stereochemically pure (3S,4R,4aR, 10aS)-6-amino-3,4,4a,5,10,10a-hexahydro-8-(methylthio)-2H-pyrano[3,2-g]pteridine-3,4-diol ( 8 ) and its corresponding enantiomer 9 , respectively Structure 8 was proven by X-ray analysis. Acylation of the hexahydropyrano[3,2-g]pteridines yielded the more stable tri-, tetra-, and pentaacetyl derivatives 12–14, 20–23, 27–32 , and 37–39 which were characterized and of which the absolute and relative configurations were determined (¹H- and ¹³C–NMR and UV spectra, chiroptical measurements, elemental analyses).     

Electron-Nuclear Double Resonance Study of Flavodoxin from Peptostreptococcus Elsdenii

The proton electron-nuclear double resonance (ENDOR) of the semiquinone of Peptostreptococcus elsdenii flavodoxin has been studied at – 155°. Studies with flavodoxin derivatives in which the natural coenzyme has been replaced by C(8)? CD₃,? C(9)? D? , C(6,9)? D₂? , and iso-FMN² have made it possible to unequivocally assign the ENDOR lines to C(8)? CH₃ and C(6)? H.     

On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels–Alder Reactions

Intramolecular Diels–Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6‐31+G(d) and CBS‐QB3 levels of theory for a series of 1,3,8‐nonatrienes, H₂C?CH? CH?CH? CH₂? X? Z? CH?CH₂ [? X? Z? =? CH₂? CH₂? ( 1 ); ? O? C(?O)? ( 2 ); ? CH₂? C(?O)? ( 3 ); ? O? CH₂? ( 4 ); ? NH? C(?O)? ( 5 ); ? S? C(?O)? ( 6 ); ? O? C(?S)? ( 7 ); ? NH? C(?S)? ( 8 ); ? S? C(?S)? ( 9 )]. For each system studied ( 1 – 9 ), cis‐ and trans‐TS isomers, corresponding, respectively, to endo‐ and exo‐positioning of the ? C? X? Z? tether with respect to the diene, have been located and their relative energies (E_rel^TS) employed to predict the cis/trans IMDA product ratio. Although the E_rel^TS values are modest (typically <3 kJ mol^?1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (X?O→NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis‐TS, namely (1) unfavorable torsional (eclipsing) strain about the C4? C5 bond, that is caused by the ? C? X? C(?Y)? group’s strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo‐(thio)carbonyl group, C?Y, and the diene. The former interaction predominates when X is weakly electronegative (X?N, S), while the latter is dominant when X is more strongly electronegative (X?O), or a methylene group (X?CH₂) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1 , 2 , 3 , and 4 (published work) and 5 , 6 , and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans‐selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14 , which undergoes a more trans‐selective IMDA reaction than the corresponding ester tethered precursor 13 .     

Ab initio studies of structural features not easily amenable to experiment. 42. Molecular geometries and conformational analysis of methylbutanoate

Conformational energy profiles were calculated for τ₁, the C? C? C?O torsion, and τ₂, the C? C? C? C torsion, of methyl butanoate, using Pulay's ab initio gradient procedure at the 4-21G level with geometry optimization at each point. In addition, the structures of seven conformations were fully relaxed, including the energy minima (τ₁, τ₂) = (0, ?60), (0, 180), (120, 180), (120, ?60), and the maxima (0, 0), (180, 180), and (60, ?60). The calculated geometries confirm the previously formulated rule that, in saturated hydrocarbons, a C? H bond trans to a C? C bond (C? H_s) is consistently shorter than a C? H bond (C? H_a) trans to another C? H bond. Specifically, for X? C(α) (? O)? C(β)? C(γ)? C(δ) systems, the following rules can be formulated, incorporating results from previous studies of butanal, butanoic acid, and 2-pentanone: (1) C(δ)? H_s < C(δ)? H_a in all the conformers in which the δ-methyl group is remote from the ester group; whereas, in all the conformers in which nonbonded interactions are possible between the C(δ)-methyl and the ester groups, the bonding pattern is affected by a C? H ?O?C interaction. (2) In the most stable conformers, (0, 60), C(β)? H_a < C(β)? H_s, and C(γ)? H_a < C(γ)? H_s, regardless of X. (3) The average C? C bonds in the τ₂ = 180° conformers are consistently shorter than those with τ₂ = 60° (compared at τ₁ constant). In the most stable conformations (τ₁ = 0°, τ₂ = 60° or 180°), the bonding sequence is consistently C(α)? C(β) < C(β)? C(γ) < C(γ)? C(δ); whereas, when τ₁ = 120°, C(α)? C(β) < C(β)? C(γ) > C(γ)? C(δ).     

1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P?C) and J(P?H)

All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R₂P(X)? C?C? H and R₂P(X)? C?C? CH₃ (X ? oxygen, lone pair and R ? C₆H₅, N(CH₃)₂, OC₂H₅, N(C₆H₅)₂, Cl) from ¹H and ¹³C NMR spectra. In P^IV derivatives the following signs are obtained: ¹J(P? C)+, ²J(P? C)+, ³J(P? C)+, ³J(P? H)+, ⁴J(P? H)? . Linear relations are observed between ¹J(P? C), ²J(P? C) and ³J(P? C) versus ³J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for ¹J(P? C) and ²J(P? C). In P^III derivatives these signs are: ¹J(P? C)- and +, ²J(P? C)+, ³J(P? C)-, ³J(P? H)-, ⁴J(P? H)+. Only ³J(P? C) and ³J(P? H) reflect a small contribution of the Fermi contact term while in ¹J(P? C) and ²J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.     

Pteridine studies: III—13C n.m.r. data of pteridine,some of its derivatives and their covalent σ-adducts with ammonia and water

¹³C n.m.r. spectral data of pteridine and nineteen of its derivatives (containing one or more chloro, methylthio, methyl, t-butyl or phenyl substituents) are reported. The ¹³C n.m.r. spectrum of the title compound has been assigned conclusively. ¹³C n.m.r. substituent effects are shown to be very useful in discerning between 6- and 7-substituted pteridines. Additionally, the ¹³C n.m.r. spectra of several covalent amination products, i.e. the 3,4-dihydro-4- amino- and the 5,6,7,8-tetrahydro-6,7-diaminopteridine derivatives, formed by dissolving the appropriate pteridine in liquid ammonia, have been recorded. The ¹³C n.m.r. spectra of the corresponding covalent hydrates are also reported.     

Photochemische Reaktionen. 103. Mitteilung [1]. Zur Photochemie konjugierter Epoxy-en-carbonylverbindungen der Jonon-Reihe: UV.-Bestrahlung α,β-ungesättigter ε-Oxo-γ, δ-epoxy-carbonylverbindungen und Untersuchung des Mechanismus der Epoxy-enon/Furan-Isomerisierung

The Photochemistry of Conjugated γ,δ-Epoxy-ene-carbonyl Compounds of the Ionone Series: UV.-Irradiation of α,β-Unsaturated ε-Oxo-γ,δ-epoxy Compounds and Investigation of the Mechanism of the Isomerization of Epoxy-enones to Furanes On ¹n, π*-excitation (λ ≥ 347 nm; pentane) of the enonechromophore of 3 , three different reactions are induced: (E/Z)-isomerization to give 13 (7%), isomerization by cleavage of the C(γ)–C(δ) bond to yield the bicyclic ether 14 (36%) and isomerization by cleavage of the C(γ)? O bond to give the cyclopentanones 15 (13%) and 16 (11%; s. Scheme 2). On ¹π, π*-excitation (λ = 254 nm; acetonitrile) 13 (14%), 15 (6%), and 16 (6%) are formed, but no 14 is detected. In contrast, isomerization by cleavage of the C(δ)? O bond to give the cyclopentanone 17 (23%) is observed. The reaction 3 → 17 appears to be the consequence of an energy transfer from the excited enone chromophore to the cyclohexanone chromophore, which then undergoes β-cleavage. Irradiation of 4 with light of λ = 254 nm (pentane) yields the analogous products 20 (18%), 21 (9%), 22 (7%), and 24 (7%; s. Scheme 2). Selective ¹n, π*-excitation (λ ≥ 280 nm) of the cyclohexanone chromophore of 4 induces isomerization by cleavage of the C(δ)? O bond to give the cyclopentanones 23 (9%) and 24 (44%). Triplet-sensitization of 4 by excited acetophenone induces (E/Z)-isomerization to provide 20 (12%) and isomerization by cleavage of the C(δ)? O bond to yield 21 (26%) and 22 (20%), but no isomerization via cleavage of the C(δ)? O bond. It has been shown, that the presence of the ε;-keto group facilitates C(γ)? C(δ) bond cleavage to give a bicyclic ether 14 , but hinders the epoxy-en-carbonyl compounds 3 and 4 from undergoing cycloeliminations. The activation parameters of the valence isomerization 13 → 18 , a thermal process, have been determined in polar and non-polar solvents by analysing the ¹H-NMR. signal intensities. The rearrangement proceeds faster in polar solvents, where the entropy of activation is about ?20 e.u. Opening of the epoxide ring and formation fo the furan ring are probably concerted.     

Conformational study of phosphoserine in aqueous solutions. II—1H n.m.r. results

The 270 MHz n.m.r. spectra of phosphoserine (PSer) have been measured and completely analysed for seven pD values. The resulting vicinal coupling constants ³J(HαHβ) and ³J(PHβ) are used to discuss the conformations of PSer with respect to the (Hα)? Cα? Cβ? (O) and (Cα)? Cβ? O? (P) bond axes. The all-trans conformer predominates for all pD values, with its fractional population being minimal at pD values close to neutrality. The Cβ? O bond rotamer populations agree reasonably well with those obtained from ¹³C investigations.     

C（sp3）-H bond functionalization of oximes derivatives via 1,5-hydrogen atom transfer induced by iminyl radical

Oximes derivatives have been vastly used in organic synthesis. In this review, C（sp³）-H bond functionalization of oximes derivatives via iminyl radical induced 1,5-hydrogen atom transfer was discussed. According to the different type of products, this review was divided into three parts:（1） C（sp³）-H bond functionalization for C-C bond formation.（2） C（sp³）-H bond functionalization for C-N bond formation.（3） C（sp³）-H bond functionalization for C-S, C-F b...     

Synthese von Humaninsulin. II. Aufbau des cyclischen Fragments A(1–13)

Synthesis of human insulin. II. Preparation of the A(1–13) fragment. The present report gives a detailed account of the synthesis of the protected tridecapeptide A(1–13), Boc? Gly? Ile? Val? Glu(OBu^t)? Gln Ser(Bu^t)? Leu? OH ( 20 ), an essential intermediate in the recently published total synthesis of human insulin [1]. The main feature in the synthesis of 20 was the specific formation of a disulfide bond between A6 and A11 in the presence of an additional cysteine residue (A7). The selective ring closure was accomplished with the segment A(6–13), H? Cys(Trt)? Cys(Acm)? Thr(Bu^t)? Ser(Bu^t)? Ile? Cys(Trt)? Ser(Bu^t)? Leu? OH ( 18 ), which was obtained by way of conventional synthesis routes. Treatment of 18 with iodine in trifluoroethanol formed the desired disulfide bridge from the two S-trityl-cysteine residues without affecting the S-acetamidomethyl-protected cysteine A7. A final azide coupling with the N-terminal derivative A(1–5) ( 3 ) provided the tridecapeptide fragment 20 as a crystalline compound.     

Photochemical reactions. 144th Communication. Photochemistry of 5,6-epoxy-1,3-dienes in the ionone series: Influence of a methoxy group in position 7

On triplet excitation (λ > 280 nm, acetone), the epoxydiene (E)- 5 undergoes initial cleavage of the C(5)? O bond of the oxirane and subsequent cleavage of the C(6)? C(7) bond leading to the diradical intermediate e which reacts by recombination furnishing the cyclic compounds (E/Z)- 6 , (E/Z)- 7,8 , and 9 . Alternatively, a H -shift leads to the aliphatic methyl-enol ether 10 which undergoes a photochemical [2+2]-cycloaddition to compounds 12 and 13 , the main products on triplet excitation of (E)- 5 . On singlet excitation (λ = 254 nm, MeCN), (E)- 5 undergoes cleavage to the carbene intermediates f and g . The vinyl carbene f reacts with the adjacent double bond furnishing the cyclopropene 14 as the main product. From the carbene intermediate g , the methyl-enol ether 15 arises by carbene insertion into the neighboring C? H bond. Furthermore, the diastereomer of the starting material, the epoxydiene (E)- 16 , and compounds 17A+B are formed via the ylide intermediate h . Finally, the cyclobutene 18 is the product of an electrocyclic reaction of the diene side chain.     

Crystal structure of a liquid crystal non‐symmetric dimer: cholesteryl 4‐[4‐(4‐n‐butylphenylethynyl)phenoxy]butanoate

The crystal structure of cholesteryl 4‐[4‐(4‐n‐butylphenylethynyl)phenoxy]butanoate [phase sequence: Cr 155°C (46.1?J?g^?1) SmA 186.8°C (1.5?J?g^?1) TGB‐N* 204.7 (6?J?g^?1) I] has been solved from single crystal X‐ray diffraction data. The compound crystallizes in the monoclinic space group P2₁ with unit cell parameters: a?=?13.129(2), b?=?9.3904(10), c?=?17.4121(8)?Å, β?=?92.790(7)°, Z?=?2. The structure has been solved by direct methods and refined to R?=?0.0606 for 3?250 observed reflections. The bond distances and angles are in good agreement with the corresponding values for compounds containing phenyl and cholesterol moieties. The phenyl rings A and B are planar. The dihedral angle between the least‐squares planes of the two phenyl rings is 28°. The cholesterol moiety has the usual structure: the C and E rings have chair conformations, and the D and F rings adopt half‐chair conformations. The molecules in the unit cell are arranged in an antiparallel manner. The crystal structure is stabilized by an intermolecular C–H…O contact of 2.989(10)?Å.     

Preparation,Structure, and Reactivity of Thioxo and Imino Derivatives of the Triolide (and Pentolide) from (R)-3-Hydroxybutanoic Acid

Reaction of the triolide 1 from (R)-3-hydroxybutanoic acid with Lawesson's reagent 5 leads to the mono-, di-, and trithio derivatives 6–8 which can be isolated in pure form (20–40% yields), and which have crystal structures very similar to the parent triolide 1 (Fig. 1). Similarly, pentolide 3 is converted to mixtures of various thio derivatives, three of which are separated ( 10–12 ) by HPLC and fully characterized. The X-ray structures of the mono- and of one of the dithiopentolides ( 10, 12 ) differ remarkably from each other (Fig. 3). Reduction of the thiotriolides 6–8 (NaBH₄, R₃SnH, Cl₃SiH, Raney-Ni) gives 12-membered rings containing up to three ether groups (chiral crown ethers, 15, 17–19 ) in poor yields. The thiotriolides react spontaneously and in yields of up to 96% with ammonia, certain primary amines, and hydroxylamine to give imine and oxime derivatives with intact 12-membered-ring backbones ( 20, 22–24, 30 , see crystal structures in Figs. 4–7). The rigid structure of all the derivatives of triolide 1 puts the C?O, C?S, and C?NR O-, S-, and N-atoms in juxtaposition (a feature reminiscent of the side chains in the iron-binder enterobactin, Fig. 6). Imines containing PPh₂ groups are prepared ( 30, 33, 35 ) from the thiotriolides and tested as chiral ligands for Pd^II-catalyzed 1,3-diphenyallylations (→ 37 , enantiomer ratio up to 77:23). The reactions described demonstrate that multiple reactions of the triolide 1 from (R)-3-hydroxybutanoic acid which proceed through tetrahedral intermediates are possible without ring opening – the skeleton is remarkably stable, and this might be exploited as a template for bringing up to three pendent substituents into close proximity to allow a study of their interactions and cooperative properties. Also, the di- and trithio derivatives 7 and 8 could be used for cross-linking in molecules containing primary NH₂ groups.     

Zur Reaktion von Diphenoxyphosphorylchlorid mit N,N-disubstituierten Harnstoffen – Bildung von phosphorylierten Biuret-Verbindungen

Reaction of Diphenoxyphosphorylchloride with N,N-disubstituted Ureas – Formation of Phosphorylated Biuret Compounds N′,N′-disubstituted N-diphenoxyphosphorylureas, (PhO)₂P(O)? NH? CO? NR¹R² (R¹ = R² = Et, 1 ; n-Pr, 2 ; n-Bu, 3 ; i-Bu, 4 ; R¹ = Me and R² = Ph, 5 ) as well as phosphorylated biuret compounds, (PhO)₂P(O)? NH? CO? NH? CO? NR¹R² are obtained in the reaction of diphenoxyphosphorylchloride with N,N-disubstituted ureas and triethylamine. The biuret derivatives are formed via (PhO)₂P(O)NCO. Their yield rises if the reaction is carried out without amine. The X-ray crystal structure analysis of (PhO)₂P(O)? NH? CO? NH? CO? NPr₂, 8 , shows that dimers exist in the crystal with intermolecular as well as intramolecular hydrogen bonds. The framework formed by atoms P? N1? C1(O4)? N2? C2(O5)? N3(C3)C6 is planar. The existence of a rotation barrier along the bond C2–N3 was detected by NMR spectroscopy.     

Hydrogenation of the ansa-Chain of Rifamycins. X-ray crystal structure of (16S)-16,17,18,19-tetrahydrorifamycin S

The catalytic hydrogenation of rifamycin S ( 2 ) over Pd/C, followed by oxidation with K₃[Fe(CN)₆], generates a pair of 16,17,18,19-tetrahydrorifamycins S ( 3/4 ), epimeric at C (16). The use of PtO₂ as catalyst leads to the hydrogenation also of the C(28)?C(29) bond giving, after oxidation by K₃[Fe(CN)₆], a mixture of the epimers (16R)- and (16S)-16,17,18,19,28,29-hexahydrorifamycins S ( 5/6 ). Furthermore, we synthesized the (16R)- and (16S)-3-bromo derivatives 7/8 and (16R)- and (16S)-3-(piperidin-1-yl) derivatives 9/10 . The determination of the X-ray crystal structure of the most abundant epimer 4 of the tetrahydrorifamycins allowed the assignment of the absolute configuration at C(16) of all derivative. A Structure-activity relationship study showed that in general the (16R)-epimers are more potent inhibitors of bacterial RNA polymerase than the (16S)-epimers.     

Reactivity in the gas phase. Behaviour of isoxazoles under negative ion chemical ionization conditions

[M ? H⁺]^? ions of isoxazole (la), 3-methylisoxazole (1b), 5-methylisoxazole (1c), 5-phenylisoxazole (1d) and benzoylacetonitrile (2a) are generated using NICI/OH^? or NICI/NH₂^? techniques. Their fragmentation pathways are rationalized on the basis of collision-induced dissociation and mass-analysed ion kinetic energy spectra and by deuterium labelling studies. 5-Substituted isoxazoles 1c and 1d, after selective deprotonation at position 3, mainly undergo N ? O bond cleavage to the stable α-cyanoenolate NC ? CH ? CR ? O^? (R = Me, Ph) that fragments by loss of R? CN, or R? H, or H₂O. The same α-cyanoenolate anion (R = Ph) is obtained from 2a with OH^?, or NH₂^?, confirming the structure assigned to the [M ? H⁺]^? ion of 1d, On the contrary, 1b is deprotonated mainly at position 5 leading, via N? O and C(3)? C(4) bond cleavages, to H? C ≡ C? O ^? and CH₃CN. Isoxazole (1a) undergoes deprotonation at either position and subsequent fragmentations. Deuterium labelling revealed an extensive exchange between the hydrogen atoms in the ortho position of the phenyl group and the deuterium atom in the α-cyanenolate NC ? CD = CPh ? O^?.     

Synthesis of an Isotopically Isomeric Mixture of 1,4,6,8-Tetramethyl[13C2]azulene and Its Thermal Reaction with Dimethyl Acetylenedicarboxylate

Sodium [1,3-¹³C₂]cyclopentadienide in tetrahydrofuran (THF) has been prepared from the corresponding labelled [¹³C₂]cyclopentadiene which was synthesized from ¹³CO₂ and (chloromethyl)trimethylsilane (cf. Scheme 10) according to an established procedure. It could be shown that the acetate pyrolysis of cis-cyclopentane-1,2-diyl diacetate (cis- 22 ) at 550 ± 5° under reduced pressure (60 Torr) gives five times as much cyclopentadiene as trans- 22 . The reaction of sodium [1,3-¹³C₂]cyclopentadienide with 2,4,6-trimethylpyrylium tetrafluoroborate in THF leads to the formation of the statistically expected 2:2:1 mixture of 4,6,8-trimethyl[1,3a-¹³C₂], -[2,3a-¹³C₂]-, and -[1,3-¹³C₂]azulene ( 20 ; cf. Scheme 7 and Fig. 1). Formylation and reduction of the 2:2:1 mixture [¹³C₂]- 20 results in the formation of a 1:1:1:1:1 mixture of 1,4,6,8-tetramethyl[1,3-¹³C₂]-, -[1,3a-¹³C₂]-, -[2,3a-¹³C₂]-, -[2,8a-¹³C₂]-, and -[3,8a-¹³C₂]azulene ( 5 ; cf. Scheme 8 and Fig. 2). The measured ²J(¹³C, ¹³C) values of [¹³C₂]- 20 and [¹³C₂]- 5 are listed in Tables 1 and 2. Thermal reaction of the 1:1:1:1:1 mixture [¹³C₂]- 5 with the four-fold amount of dimethyl acetylenedicarboxylate (ADM) at 200° in tetralin (cf. Scheme 2) gave 5,6,8,10-tetramethyl-[¹³C₂]heptalene-1,2-dicarboxylate ([¹³C₂]- 6a ; 22%), its double-bond-shifted (DBS) isomer [¹³C₂]- 6b (19%), and the corresponding azulene-1,2-dicarboxylate 7 (18%). The isotopically isomeric mixture of [¹³C₂]- 6a showed no ¹J(¹³C,¹³C) at C(5) (cf. Fig. 3). This finding is in agreement with the fact that the expected primary tricyclic intermediate [7,11-¹³C₂]- 8 exhibits at 200° in tetralin only cleavage of the C(1)? C(10) bond and formation of a C(7)? C(10) bond (cf. Schemes 6 and 9), but no cleavage of the C(1)? C(11) bond and formation of a C(7)? C(11) bond. The limits of detection of the applied method is ≥96% for the observed process, i.e., [1,3a-¹³C₂]- 5 + ADM→ [7,11-¹³C₂]- 8 →[1,6-¹³C₂]- 9 →[5,10a-¹³C₂]- 6a (cf. Scheme 6).     

Synthesis,crystal structure,and catalytic performance of two 3-D supramolecular compounds: (C7N2H7)3(C7N2H6) · PMo12O40 · 2H2O and (C7N2H7)3(C7N2H6)2 · AsMo12O40 · 3H2O

Two organic–inorganic compounds based on Keggin building blocks have been synthesized by hydrothermal methods, (C₇N₂H₇)₃(C₇N₂H₆)?·?PMo₁₂O_40?·?2H₂O (1) and (C₇N₂H₇)₃(C₇N₂H₆)_2?·?AsMo₁₂O_40?·?3H₂O (2) (C₇N₂H₆?=?benzimidazole). Single-crystal X-ray analysis revealed that 1 crystallized in the triclinic system, P-1 space group with a?=?9.8980(4)?Å, b?=?11.2893(4)?Å, c?=?25.8933(9)?Å, α?=?93.307(2)°, β?=?90.630(2)°, γ?=?108.330(2)°, V?=?2740.68(18)?ų, Z?=?2, R ₁(F)?=?0.0740, ωR ₂(F ²)?=?0.1511, and S?=?1.037; 2 crystallized in the triclinic system, P-1 space group with a?=?12.3353(4)?Å, b?=?13.2649(4)?Å, c?=?20.2878(6)?Å, α?=?95.6630(10)°, β?=?100.1720(10)°, γ?=?99.3940(10)°, V?=?3195.72(17)?ų, Z?=?2, R ₁(F)?= 0.0329, ωR₂ (F ²)?=?0.1236, and S?=?1.088. The two compounds show a layer framework constructed from Keggin-polyoxoanion clusters and benzimidazole via hydrogen bonds and π–π stacking interactions, resulting in a 3-D supramolecular network. Both have high catalytic activity for oxidation of methanol. When the initial concentration of the methanol is 5.37?g?m^?3 in air and the flow velocity is 4.51?mL?min^?1, methanol is completely eliminated at 150°C for 1 (160°C for 2).     

Heterocycles. CLXIX. Barriers to rotation in some N,N-Dimethyl-N′-heteroaryl,N,N-Diethyl-N′-heteroaryl-substituted formamidines and N,N-Dimethyl-N′-heteroaryl-substituted acetamidines

The free energies of the rotational barriers, ΔG*, about ?CH? NMe₂ bond in N′-heteroaryl N,N-dimethylformamidines (A), about ?CH? NEt₂ bond in N-heteroaryl N,N-diethylformamidines (B), and about ?C(Me)? NMe₂ bond in N′-heteroaryl N,N-dimethylacetamidines (C) have been found to be in the range 17.5–20.1 kcal/mole for type A, 18.8–21.6 kcal/mole for type B and 13–14 kcal/mole or below for type C of compounds, respectively. The compounds of the types A and B exist in the forms IIa, IIIa, IV, V, and VI, while the compounds of the type C exist in the forms IIb and IIIb.     

Pteridines. Part XCVII. Synthesis and properties of 6-thioxanthopterin and 7-thioisoxanthopterin

6-Thioxanthopterin ( 13 ) was synthesized in four steps starting from 2-amino-4-(penthyloxy)pteridine ( 3 ) via the 8-oxide 4 , its subsequent interconversion to the 6-chloro ( 7 ) and 6-thio derivative ( 12 ) and final hydrolysis of the pentyloxy group. 7-Thioisoxanthopterin ( 15 ) was derived analogously from 2-amino-4-(pentyloxy)pteridine-7(8H)-thione ( 14 ) by alkaline hydrolysis. The various 6- and 7-thiopteridines were methylated to give the corresponding 6- ( 10, 11 ) and 7-(methylthio) derivatives ( 16, 17 ). The newly synthesized compounds have been characterized by elemental analyses, their UV spectra, and the determination of the acidic and basic pK_a values. The spectral relationships are discussed in detail.