13C-NMR-Spektren von Tetracyclo[4.1.0.02,4.03,5]heptanen,Tetracyclo[5.1.0.02,4.03,5]octanen und Tricyclo[4.1.0.02,7]hept-3-enen. Ungewöhnliche δ- und γ-Substituenteneffekte

Carbon-13 NMR spectroscopic data of eleven tetracyclo[4.1.0.0^2,4.0^3,5]heptanes, two tetracyclo-[5.1.0.0^2,4.0^3,5]octanes and twelve tricyclo[4.1.0.0^2,7]hept-3-enes are reported. In the tetracycloheptanes, halogens located at the 7-position cause large δ substituent effects. endo-Halogens shift the C-4 signal to lower field by about 6 ppm, while exo-haolgens produce upfield shifts of the C-3 signal, which are dependent on the nature of the halogen and reach a maximum of 9.1 ppm in the case of fluorine. An orbital model is proposed to explain the δ upfield shifts. The compounds containing fluorine reveal a connection between the δ substituent effects and the corresponding ¹³C? ¹⁹F coupling constants. Substituents in the 5 position of tricycloheptenes are γ-substituents of C-1, C-3 and C-7 and produce downfield shifts of the absorptions of these nuclei. Their dependence on the nature of the substituent follows approximately those in 1-substituted adamentanes; in the case of C-7, however, their magnitude by far exceeds the adamantane values, bromine (15.5 ppm) being most effective.     

Carbon-13 nuclear magnetic resonance spectra. VIII—18α- and 18β-glycyrrhetic acid derivatives

The ¹³C NMR data of six pairs of 18α/18β-glycyrrhetic acid derivatives are presented. It is shown that the configuration at C-18 can easily be recognized by inspecting the chemical shifts of several characteristic carbons, e.g. C-12, C-13, C-18 and C-28. The shifts of these carbons originated by the change of the D/E ring junction proved to be largely independent of the substitution at C-3 and C-20.     

13C NMR of organosulfur compounds the 13C chemical shifts of monocyclic γ- and δ-sultones

The ¹³C NMR spectra of several monocyclic γ-sultones(1,2-oxathiolane 2,2-dioxides) and δ-sultones(1,2-oxathiane 2,2-dioxides) have been determined and are presented herein. The chemical shifts of the ring carbons of these compounds are compared in terms of conformational, electronic and anisotropic differences. Electric field effects may be responsible for the chemical shifts of the C-α carbon, but do not appear to be important for C-α. Anisotropic deshielding also appears to be important for the chemical shifts of C-α, but the effects on C-α appear to be small. Dipole changes at C-α and C-α, induced by back donation of electron density from the ring oxygen to sulfur, may explain the chemical shifts at C-α. Substituent effects are readily explained in terms of well-known effects. In general, the carbons closest to the sulfonate group are found to be the most affected, and the carbons of the δ-sultones proximate to the sulfonate group are found to be more deshielded than those of the γ-sultones.     

The structure of α-(1,2-dithiole-3-ylidene) ketones and α-(1,2-dithiole-3-ylidene) aldehydes studied by means of n.m.r. spectroscopy

1H and ¹³C n.m.r. studies of a series of twelve 1,2-dithiole-3-ylidene ketones and aldehydes have shown that the geometry of the carbon backbone is the same as found in 1,6,6aλ⁴-trithiapentalenes. No evidence has been found which favours a bicyclic structure for the system. A linear correlation of observed ¹³C chemical shifts with calculated charge densities is found to be valid. The observations are in agreement with a structure which is a hybrid between a true ketonic structure and a true mesoionic structure. By using the difference in the ¹³C chemical shifts of ortho and meta carbon atoms in substituent phenyl groups it is possible to qualify the degree of coplanarity of the phenyl groups with the backbone of the molecule.     

Prediction of ortho(β) 13C chemical shifts in conjugated systems

An equation has been developed which relates ortho or C-β ¹³C substituent chemical shifts (SCS) to the ortho proton–proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predict ortho ¹H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived from ortho ¹³C data in 2-naphthalenes and monosubstituted benzenes and its application to other unsaturated series is discussed.     

Investigation of the torsional angle at the glycosidic bond in 5′-amino-5′-deoxythymidine derivatives by carbon-13 n.m.r. spectroscopy

The conformational preference of the thymine base ring with respect to the sugar ring in β,β,β,-trichloroethyl 5′amino-5′-deoxythymidine-5′-phosphate has been studied by ¹³C n.m.r. spectroscopy. The magnitude of the three bond vicinal coupling constant, J(C-2, H-1′), for β,β,β-trichloroethyl 5′-amino-5′-deoxythymidine-5′-phosphate and the similarity between the chemical shifts for the furanose carbons C-1′, C-2′, and C-3′ in β,β,β-trichloroethyl 5-′-amino-5′-deoxythymidine-5′-phosphate and in β,β,β-trichloroethyl thymidine 5′-phosphate indicate that the amino analogue exists in aqueous solution predominantly in the anti conformation, as is the case with natural nucleotides.     

Synthesis of 2′-amino-17-cyclopropylmethyl-6,7-dehydro-3,14-dihydroxy-4,5α-epoxy-6,7:4′,5′-thiazolomorphinan from naltrexone

Fusion of an azole moiety at C-6 and C-7 of naltrexone ( 1 ) is illustrated by the synthesis of the title compound 8 . Bromination of 3-O-methylnaltrexone led to the 1,7α-dibromo derivative which reacted with thiourea to attach the 2-aminothiazole ring to C-6 and C-7 of naltrexone. After converting the amino and alcohol groups to trimethylsilyl derivatives, the aromatic bromo group was removed by halo-lithium interchange with butyllithium, followed by hydrolysis with water. In the final step of the synthesis, the methyl ether was cleaved by boron tribromide to generate 8 . An alternate synthesis of 8 commenced with 3-O-acetylnaltrexone ( 9 ). Bromination of 9 in acetic acid in the presence of hydrobromic acid produced a mixture of 3-O-acetyl-7α-bromonaltrexone ( 10 ) and 7α-bromonaltrexone ( 11 ), both, as hydrobromides. Reaction of this mixture with thiourea furnished 8 (62% from 1 ). While ¹H and ¹³C chemical shifts of all compounds are reported, those of 11 hydrobromide and 8 dihydrochloride were established unequivocally.     

Investigation of substituent effects on the 1H and 13C NMR spectra of (Z)-N-(arylmethylene)-arylamine N-oxides (α,N-diaryl nitrones)

Substituent effects on the ¹H and ¹³C chemical shifts of 18 differently substituted (Z)-α,N-diaryl nitrones [N-(p-X-benzylidene)phenylamine N-oxides (Series I) and N-(benzylidene)-p-Y-phenylamine N-oxides (Series II)] have been obtained. A correlation has been found between the chemical shifts of the azomethine proton (H-α) and the Hammett σ parameters and the Swain and Lupton F and R parameters. Correlations of the chemical shifts of C-1 and C-4′ in Series I, and of C-α and C-1′ in Series II, with the same parameters have been investigated. In addition, the chemical shifts of the aromatic protons and carbons of the p-disubstituted (m-disubstituted in one case) benzene rings correlated with the appropriate substituent increments (Z_i). These correlations confirm the dual behaviour of the nitrone group and the presence of through-resonance in these nitrones.     

Carbon Magnetic Resonance Spectra of α, β, γ, δ- and α, β, α′, β′- Unsaturated Ketones

Carbon-13 spectra of a series of 26 unsaturated ketones (ortho- and para-cyclo-hexadienones and corresponding open-chain analogues) have been measured by Fourier-transform. Pulse spectroscopy. A complete analysis has been achieved by means of double resonance experiments using noise-modulated and coherent off-resonance proton irradiation and with the aid of non-decoupled spectra. Chemical shifts are interpreted in terms of charge distribution in the dienone system and of methyl substituent effects. Carbon chemical shifts were also obtained for O-protonated ortho- and para-cyclohexadienones. One-bond and long-range carbon-proton and carbon-fluorine spin coupling constants are reported for several compounds.     

Applications of 95Mo NMR. 5—substituent effects in the 95Mo and 13C NMR spectra of benzyltricarbonyl(η5-cyclopentadienyl)molybdenum(II) derivatives

A systematic study has been made of the effects of substituent induced chemical shifts in [(η⁵-C₅H₅)(CO)₃Mo(CH₂C₆H₄R)] compounds. Both ⁹⁵Mo and ¹³C NMR shifts in the aromatic ring are reported. The (η⁵-C₅H₅)(CO)₃MoCH₂? group is a reasonably strong resonance donor (σ_R° = ?0.21) and weak inductive donor (σ_I = ?0.07). The molybdenum chemical shifts are extremely sensitive to the effects of distant substituents (range c. 40 ppm). Since the shift correlates well with substituent constants in this series, it is suggested that the chemical shift is controlled by the paramagnetic term for this spin 5/2 nucleus.     

Substituent effects on 13C and 1H chemical shifts in 3-benzylidene-2,4-pentanediones

Substituent effects on the ¹³C and ¹H chemical shifts have been studied for derivatives of 3-benzylidene-2, 4-pentanedione. A significant correlation has been found between chemical shifts of the Z carbonyl group (C-2) and Hammett constants, while no correlation has been found for the E carbonyl group (C-4). Attempts have been made to determine the structural factors which influence these effects. The conformation of 3-benzylidene-2, 4-pentanediones has been determined by ¹³C and ¹H NMR spectroscopy.     

Carbon-13 NMR and conformational analysis of meso- and dl-α,α′-disubstituted succinic acids

meso-and dl-Diastereomers of a number of α,α′-disubstituted succinic acids have been shown to give different ¹³C NMR chemical shifts. The results can be satisfactorily explained on the basis of their conformational analyses. A discussion of the observed chemical shifts is presented, and the preferred conformation for each of several compounds is predicted on the basis of these chemical shifts.     

Synthesis of 3β-Hydroxy[21-14C]-5β-pregn-8(14)-en-20-one from Chenodeoxycholic Acid

3β-Hydroxy[21-¹⁴C]5β-pregn-8(14)-en-20-one ( 17 ) was prepared from chenodeoxycholic acid ( 1a ). The synthetic sequence involved: (i) degradation of the bile-acid side chain to an etianic acid; (ii) formation of the 8(14)-double bond; (iii) inversion of the configuration at C(3); (iv) construction of the acetyl side chain at C(17) with the required isotopic label at C(21). Structures of all described products were confirmed by chemical and spectroscopic (IR, ¹H-NMR, ¹³C-NMR, MS) methods.     

Geometrical isomerism and 13C spectra of the β-substituted Enones R1?C(1)O?C(2)HC(3)H?R2

The ¹³C chemical shifts of the unsaturated carbons were measured in 31 cis and trans pairs of β-substituted enones R₁? C(1)O? C(2)H?C(3)H? R₂. In these polarized ethylenes the chemical shifts of the olefinic carbons are simply related by the equation δ_c=δ_t+A. The steric and electronic effects introduced by the R₁ and R₂ substituents influence the chemical shifts of C-2 and C-3 in both isomers. It is shown that the sign and magnitude of the intercept A mainly reflect the π-charge electronic density changes which arise in the cis isomer and are transmitted via the π-framework. The effect of the steric interaction on the chemical shift of C-3 in the cis isomers is postulated to be related to the symmetry of the substituents. Therefore, the differential shielding of C-3 is indicative of the conformational structure of the cis molecule.     

A Neutral “Aluminocene” Sandwich Complex: η1‐ versus η5‐Coordination Modes of a Pentaarylborole with ECp* (E=Al,Ga; Cp*=C5Me5)

The pentaaryl borole (Ph*C)₄BXyl^F [Ph*=3,5‐tBu₂(C₆H₃); Xyl^F=3,5‐(CF₃)₂(C₆H₃)] reacts with low‐valent Group 13 precursors AlCp* and GaCp* by two divergent routes. In the case of [AlCp*]₄, the borole reacts as an oxidising agent and accepts two electrons. Structural, spectroscopic, and computational analysis of the resulting unprecedented neutral η⁵‐Cp*,η⁵‐[(Ph*C)₄BXyl^F] complex of Al^III revealed a strong, ionic bonding interaction. The formation of the heteroleptic borole‐cyclopentadienyl “aluminocene” leads to significant changes in the ¹³C NMR chemical shifts within the borole unit. In the case of the less‐reductive GaCp*, borole (Ph*C)₄BXyl^F reacts as a Lewis acid to form a dynamic adduct with a dative 2‐center‐2‐electron Ga?B bond. The Lewis adduct was also studied structurally, spectroscopically, and computationally.     

A revised assignment of the 13C NMR spectra of α- and β-pinenes

α-Pinene and β-pinene ¹³C enriched at the C-10 position were prepared by an unambiguous synthesis. ¹³C NMR spectral analysis provided evidence for a revised assignment for α-pinene at the C-9 and C-10 carbon atoms.     

Carbon-13 nuclear magnetic resonance studies of anthraquinones. Part III—correlation of substituent effects for 2-substituted anthraquinones

The ¹³C chemical shifts of 2-substituted and 2,6-disubstituted anthraquinones have been determined and assigned. The C-1, 2, 3, 4, 13 and C-14 chemical shifts of 2-substituted anthraquinones are correlated with the chemical shifts of monosubstituted benzenes. A three-parameter correlation with Swain and Lupton's ? and ? parameters and Schaefer's Q parameter provides relationships for the prediction of all chemical shifts of 2-substituted anthraquinones from the substituent parameters. Q values for the SCH₃, OCOCH₃, C₂H₅ and C(CH₃)₃ groups are proposed. The two types of correlations are compared for predicting chemical shifts.     

Chromium Tricarbonyl η6-Complexes of (η5-Cyclopentadienyl)(η4-1,3-Diphenylcyclobutadiene)Cobalt

The reaction of (η⁵-cyclopentadienyl)(η⁴-1,3-diphenylcyclobutadiene)cobalt ( I ) with excess Cr(CO)₃py₃ in BF₃OEt₂ yielded two identified heterometallic compounds. Compounds II and III with one and two phenyl rings complcxed with Cr(CO)₃ fragment(s), respectively. These compounds were characterized by mass, infrared, ¹H and ¹³C NMR spectra and elemental analysis. The crystal structure of II was determined. The Cr(CO)₃ fragment bends inward toward the cyclobutadicne ring due to its electron-withdrawing ability, in accord with Hunter's postulate. A sharp line due to the non-complexed phenyl ring was observed in the ¹HNMR spectrum, which implies that five protons are magnetically equivalent. The chemical shifts of two protons of the cyclobutadiene ring decreased from I to II then to III , possibly because of diminished deshielding effect from the phenyl ring in (arene)Cr(CO)₃.     

Carbon-13 NMR spectra of nucleoside 3′,5′-cyclic phosphates. Proposition for revised signal assignments

On the basis of the data obtained from ¹³C NMR spectra of 8,2′-S-cycloadenosine 3′,5′-cyclic phosphate and other nucleoside 3′,5′-cyclic phosphate analogues, it is suggested that the published assignments of the C-3′ and C-4′ signals in nucleoside 3′,5′-cyclic phosphates should be reversed. According to the revised assignments, C-4′, which is fixed very closely to the diesterified phosphate group is markedly shielded (?12.5 to ?15 ppm), and the C-3′ signal shows a downfield shift (+6 to +8 ppm) which is comparable to that for the C-5′ signal, for all compounds so far measured when compared with the chemical shifts for the corresponding nucleosides. The 3′,5′-cyclic phosphates of thymidine and 8,2′-S-cycloadenosine, which have no α-OH group on C-2′, show similar chemical shift changes for the corresponding sugar carbons which are different from those observed for ribonucleoside derivatives.     

Downfield γ-gauche and γ-antiperiplanar effects on 13C NMR chemical shifts exerted by thiophene sulphur

The γ-effects of sulphur on ¹³C NMR chemical shifts have been measured in a series of steroidal compounds containing the thiophene ring in different configurations with respect to the rest of the molecule. The data constitute the first example of downfield effects exerted by sulphur on both gauche and antiperiplanar γ-carbons. The γ-gauche effect of sulphur amounts to 1.6–1.8 ppm, the γ-antiperiplanar effect from practically zero to almost 1 ppm.