Annular tautomerism in the solid state: a high resolution n.m.r. study

Elguero, José; Fruchier, Alain; Pellegrin, Valdo

doi:10.1039/c39810001207

Cited by 48 publications

(25 citation statements)

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“…The 12 lines observed for this substituent could correspond to two different conformations of the phenyl in the crystal. In any case, this compound deserves further study.3 Conclusion This study has corroborated the earlier observation (1,2) that in the solid state " r a~i d ' '~ annular tautomerism is seldom observed. The reasons why a given tautomer is preferred in the solid state are not clearly understood at the present momefit.…”

Section: With the Exception Of 3(5)-phenyl-5(3)-methylpyrazolesupporting

confidence: 77%

“…In a series of papers (1)(2)(3)(4)(5), we have shown that high resolution 13C nmr is a valuable tool for the study of tautomerism of azoles in the solid state, and, particularly, of annular tautomerism, i.e., prototropic tautomerism between nitrogen atoms (6a). In crystals, generally only one tautomer is present and, very seldom, two functional tautomers linked by hydrogen bonds have been observed by diffraction methods (6b).…”

Section: Introductionmentioning

confidence: 99%

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High resolution ¹³C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

Faure¹,

Vincent²,

Rousseau³

et al. 1988

Can. J. Chem.

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ELGUERO. Can. J. Chem. 66, 1141 (1988.Carbon-1 3 nuclear magnetic resonance spectroscopy in the solid state (cross polarization/magic angle spinning technique) is a very suitable method for studying the annular tautomerism of pyrazoles. In all the compounds studied, the tautomerism is frozen and the signals are well resolved except for 3,5-dimethyl-4-nitro pyrazole, which shows broad signals. In the case of 4-substituted derivatives of 3(5)-methylpyrazoles, the tautomer present in the solid state is a 4-X-5 methylpyrazole. 3-Phenyl-5-methylpyrazole (4H or 4-methyl) is favoured over the 3-methyl-5-phenyl tautomer.ROBERT FAURE, EMILE-JEAN VINCENT, ANDRB ROUSSEAU, ROSA MARIA CLARAMUNT et JosB ELGUERO. Can. J. Chem. 66, 1141 (1988).La resonance magnCtique nuclCaire a haute rCsolution du carbone-1 3 a 1' Ctat solide (technique polarisation croiste/rotation a I'angle magique) est une mCthode parfaitement adaptCe a 1'Ctude de la tautomCrie annulaire des pyrazoles. Pour tous les composCs CtudiCs, 1'Cchange prototropique est bloquC et les signaux sont fins et bien resolus, a l'exception de ceux du dimethyl-3,5 nitro-4 pyrazole qui sont trks Clargis. Dans le cas des dtrivCs du methyl-3(5) pyrazole substituks en position 4, la structure du tautomkre prCsent en phase cristalline est de la forme X-4 methyl-5. En ce qui conceme les dCrivCs du phCnyl-3(5) methyl-5(3) pyrazole, 1'Cquilibre tautomike est totalement dCplact vers la forme dans laquelle le mCthyle est en position 5.

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Section: With the Exception Of 3(5)-phenyl-5(3)-methylpyrazolesupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

High resolution ¹³C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

Faure¹,

Vincent²,

Rousseau³

et al. 1988

Can. J. Chem.

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“…The relative configuration in the ∆ 2 -pyrazoline ring of both adducts and esters was assigned to be trans on the basis of the values of the 1 H-NMR coupling constants for adduct 12a, menthyl ester 14g and (1R,3R,4S)-phenylmenthyl esters 20. [26] This was later confirmed by the reciprocal NOE enhancements between the hydrogen on C4 and the exocyclic CH 2 on alcohol 23 ( Figure 2). Thus, the cycloaddition is suprafacial as the stereochemical information of the dipolarophile is completely transferred to the cycloadduct.…”

Section: Methodsmentioning

confidence: 58%

α,β-Unsaturated Fischer Carbene Complexes vs. 1,3-Dipoles: Reactions with Nitrones and Nitrilimines

Barluenga¹,

Fernández-Marí

González

et al. 2000

Eur. J. Org. Chem.

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The reaction of tert‐butylalkynyl chromium Fischer carbene complex 1 with nitrones 2 affords β‐enamino‐ketoaldehydes 4 by the light‐promoted rearrangement of the corresponding [3+2] cycloadduct carbene complexes 3. On the other hand, [3+2] cycloaddition of chiral nonracemic Fischer alkenyl carbene complexes 19 with nitrilimines 10 yields enantiomerically pure Δ2‐pyrazolines with high regio‐ and diastereoselectivity.

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“…The displacements on C4 and C5 upon coordination (Table 4) are different for 1,2-Me,Im when compared with ImH and ZMeImH, but it should be remembered that these A8 values are calculated from the averaged C4/C5 signal for the latter two ligands. If the chemical shifts for uncoordinated ImH and 2-MeImH are taken from spectra in the solid state (29,38), where fast tautomeric exchange does not take place, similar shift patterns are noted for the three compounds: all ring signals are moved downfield and all methyl signals upfield. The ligand 'H chemical shifts are highly solvent-sensitive: they can vary by as much as 1 ppm by going from a protic solvent to an aromatic one (29).…”

Section: Discussionmentioning

confidence: 99%

Non-stoichiometric chloride salts of dioxotetrakis(imidazole)rhenium(V) cations

Lebuis¹,

Young²,

Beauchamp³

1993

Can. J. Chem.

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. Orange [Re02L4]C1 salts were prepared with L = imidazole and 2-methylimidazole. The presence of a strong Re=O stretching band in the infrared spectra near 785 cm-I is consistent with a trans-dioxo octahedral structure. With 1,2-dimethylimidazole, red-violet solids were obtained, which were studied by X-ray diffraction. Form I (from methanol): cubic, l a j d , a = 25.205 A, R = 0.032, 986 observed reflections; form I1 (from ethanol-dichloromethane): cubic, Ia3d, a = 25.520 A, R = 0.056, 766 observed reflections. Both materials are non-stoichiometric, containing trans-[R~O,L,]+ and protonated t r a n s -[~e~(~~) L~]~+ in an approximate ratio of 3: 1 for I and 2: 1 for 11. In both cases, the unit cell contains 1 "normal" C1-ion and 2/3 H 2 0 per complex. In form I, the additional charge of [ReO(OH)L412+ is balanced by an extra C1-ion partly occupying the unit cell origin, where it is replaced by disordered methanol the rest of the time. In form 11, Re04-and CH2Cl2 play the corresponding roles. In the infrared spectra, besides the characteristic band for the dioxo species, both forms show an extra peak at -932 cm-' originating from the protonated species, whereas form I1 shows an additional band at 907 cm-' for uncoordinated Re04-. The 'H and "C NMR spectra of both forms in D 2 0 are identical to those of the pure [R~O~L,]' salt, indicating that the protonated species is strongly acidic. ANNE-MARIE LEBUIS

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Annular tautomerism in the solid state: a high resolution n.m.r. study

Cited by 48 publications

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High resolution ¹³C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

High resolution ¹³C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

α,β-Unsaturated Fischer Carbene Complexes vs. 1,3-Dipoles: Reactions with Nitrones and Nitrilimines

Non-stoichiometric chloride salts of dioxotetrakis(imidazole)rhenium(V) cations

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Annular tautomerism in the solid state: a high resolution n.m.r. study

Cited by 48 publications

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High resolution 13C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

High resolution 13C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

α,β-Unsaturated Fischer Carbene Complexes vs. 1,3-Dipoles: Reactions with Nitrones and Nitrilimines

Non-stoichiometric chloride salts of dioxotetrakis(imidazole)rhenium(V) cations

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High resolution ¹³C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism

High resolution ¹³C nuclear magnetic resonance spectra of solid pyrazoles. Application to annular tautomerism