Synthesis and spectroscopic properties of 15n‐labelled 1,2,4‐thiadiazoles

5‐Phenyl‐1,2,4‐thiadiazole‐4‐¹⁵N and 3‐methyl‐5‐phenyl‐1,2,4‐thiadiazole‐4‐¹⁵N were synthesized from commercially available benazmide‐¹⁵N. The mass spectra and the ¹H, ¹³C, and ¹⁵N‐nmr spectra of these compounds, which show various long‐range heteronuclear coupling with the ¹⁵N‐nucleus, are discussed.     

Synthesis of 1,6-dihydro-5-hydroxy-6-oxo-3-(trifluoromethyl)-4-pyridazinecarboxylates

The reaction of 2-(alkylamino)-3-(trifluoroacetyl)butenedioates 2a-b with alkyl and aryl hydrazines in ether provides 1,6-dihydro-6-oxo-3-(trifluoromethyl)-4-pyridazinecarboxylates as their alkylamine salts 3a-g . The structures of these products are substantiated using 2D nmr and ¹⁵N nmr techniques.     

A new class of non-classical azapentalenes. Synthesis and c-13/n-15 NMR characterization of 2H-imidazo[1, 5-d]tetrazoles

The title compounds 6 (as well as the oxazoles 5 ) were obtained by thermolysis of 2-alkyl-5-(methoxycarbon-yldiazomethyl)tetrazoles 3 in benzonitrile. They were fully characterized by ¹H, ¹³C and ¹⁵N nmr spectroscopy.     

N-15 NMR analysis of 1,2,3-thiadiazoles

The ¹⁵N nmr spectra of a series of 1,2,3-thiadiazoles reveal the strong influence of substituents at C-5 on the N-2 resonance. Upon methylation, the two thiadiazole nitrogen resonances are shielded, but the most dramatic shift is observed for the methylated nitrogen, Δδ > 140 ppm. The ¹⁵N chemical shifts of some mesoionic thiadiazoles were also determined and explained by the dual effect of 5-substitution and salt formation. By disconnecting these effects, the ¹⁵N chemical shifts of 10 and 11 were found to be unusual and to reflect a thiapentalene character.     

Cryptolepinone vs. Hydroxycryptolepine: Resolution of a question of substituent functionality and double bond isomerization

An indolo[3,2-b]quinoline alkaloid bearing an N-methyl substituent at N5, and an oxygen moiety at the 11-position has been variously described as both cryptolepinone and 11-hydroxycryptolepine by independent research groups. The structure of this alkaloid is unequivocally confirmed as the former, cryptolepinone, with substantial changes in double bond isomerization relative to that which would be required if it were indeed the latter. The structure of the alkaloid was confirmed by, total assignment of the ¹H, ¹³C, and ¹⁵N nmr spectra at natural abundance using 3 mm micro inverse nmr probe technology at 400 and 500 MHz.     

A C-13 and N-15 NMR study of the syn-anti-isomerism of diazocyanides

A ¹³C and ¹⁵N nmr study seriously questions conventional explanations for $\text{syn}$-$\text{anti}$-isomerism of the named compounds and suggests an alternative modelled after singly bend and doubly bend diazo complexes with transition metal ions.     

15N- und 19F-NMR-spektroskopischer Nachweis und Xa-Austauschreaktionen der Clusteranionen [(Mo6Cl)(15NCS) X]2−, Xa = F,Cl, Br,I; n = 1–6

¹⁵N and ¹⁹F NMR Spectra and X^a-Exchange Reactions of the Cluster Anions [(Mo₆Clⁱ₈)(¹⁵NCS)^a_nX^a_6?n]^2?, X^a = F, Cl, Br, I; n = 1–6 By intermolecular ligand exchange reaction of the new compound [(Mo₆Clⁱ₈)(¹⁵NCS)^a₆] ^2? with [(Mo₆Clⁱ₆)X^a₆]^2?, X^a = F, Cl, Br, I, in acetone, the outersphere mixed cluster ions [(Mo₆Clⁱ₈)(¹⁵NCS)^a₆X^a_6?n]^2?, n = 1–6, are formed and characterized by their distinct ¹⁵N nmr chemical shifts. The ambident SCN^? is exclusively N-bonded, indicated by ¹⁵N nmr and vibrational spectra. The mixed cluster ions containing X^a = F are identified in acetonitrile by ¹⁹F nmr measurement as well. The kinetic analysis reveals equilibration at room temperature within 10 hours to statistical distribution of all compounds, inclusive the ratios for the geometric isomers for each system at any time with n = 2,4 cis:trans = 4 : 1 and n = 3 fac:mer = 2 : 3, indicating the equivalence of all X^a positions with respect to exchange reactions. For [(Mo₆Clⁱ₈)X^a₆]^2? the reaction rates increase in the series X^a = Cl < Br < I < SCN < F. The ¹⁵N nmr chemical shifts are depending on the electronegativity and the number of the X^a ligands. Furthermore an antipodal influence working on ¹⁵N trans-positioned to X^a effects an additional highfield shift for X^a = F and an additional downfield shift for X^a = Cl, Br, I.     

Synthesis and 13C, 15N NMR study of a new functionalized pyrido[2,3-b]indole derivative

New functionalized α-carbolinones especially the 4-hydroxy-3-nitro-1H,9H-pyrido[2,3-b]indol-2-one were synthesized in a good yield, three-step reaction. A complete ¹³C, ¹⁵N nmr study of this carbolinone and precursors is presented.     

Long-range 1H-15N two-dimensional heteronuclear shift correlation of the alkaloid vincamine at natural abundance

Long-range ¹H-¹⁵N heteronuclear correlation pathways in the alkaloid vincamine, a structural constituent or biogenetic congener of numerous Vinca alkaloids, are reported. Correlations were observed through the use of the GHNMQC (Gradient-enhanced Hydrogen-Nitrogen Multiple Quantum Coherence) 2D nmr experiment at natural abundance. An unanticipated four-bond coupling between the H15a resonance and N4 was observed in contrast to the typical two- and three-bond coupling pathways. Nitrogen-15 chemical shift comparisons are drawn between vincamine and structurally related alkaloids including ajmaline and the velbanamine portion of the semi-synthetic alkaloid vinorelbine (Navelbine^TM).     

Synthesis of 6-Hydroxy-2-methyl-3-thioxo-2H-1,2,4-triazin-5-one

The title compound has been prepared in three steps from 2-methylthiosemicarbazide following acylation, cyclisation and cation exchange chromatography. It was fully characterised by the usual spectroscopic means as well as by ¹⁵N nmr spectroscopy and X-ray crystallographic analysis.     

A comparison of crystallographic and NMR data for thieno[2,3‐b:4,5‐b′]dipyridine and its monohydroperchlorate salt

X‐ray crystallographic studies of thieno[2,3‐b:4,5‐b′]dipyridine ( 1 ) and its monohydroperchlorate salt ( 1a ) show that 1 is protonated at N1 in ring A and not at N6 in ring C. In each compound individual rings are planar, but there is a small dihedral angle‐of‐twist between the A and C rings. On going from 1 to 1a the largest changes in bond angles and bond lengths occur in ring A. ¹H and ^l3C nmr spectra of 1 plus the ¹³C nmr spectrum of 1a are reported.     

Synthesis and characterization of new substituted terdentate 2,6‐bis(2′‐quinolinyl)pyridine and 1,3‐bis(2′‐quinolinyl)‐benzene ligands for transition metals

A series of N‐N‐N terdendate polypyridine type ligands and their N‐C‐N cyclometalating homologues were synthetized and fully characterized (L₁‐L₁₂). Complete assignments of the ¹H spectra of the various compounds, accomplished by using a combination of one‐ and two‐dimensional nmr techniques, and ¹³C data are also reported.     

Syntheses and spectral properties of 2-Thiobiotin and biotin derivatives

A series of methylated derivatives of 2-thiobiotin (2-4) have been prepared as potential aids in elucidation of the mechanism of biotin catalysis. The syntheses and mass, infrared, ¹H nmr, and ¹³C nmr spectral properties for these substrates, their 2-thiobiotin precursors (6, 10-14) and the corresponding biotin analogs (1, 15, 31-34) are described. A series of selective proton-proton and proton-carbon decoupling experiments were employed to secure a number of the ¹H and ¹³C nmr assignments. Consistent patterns noted throughout the data set proved helpful in structure determination.     

The Structure of Silylated Amides: N-Methyl-N-Trimethylsilyltrifluoroacetamide,a Reassignment of structure

The ²⁹Si and ¹⁴N nmr spectra of some bissilylamides and monosilylamides are reported. The results are compared with those for model silylesters, amines and imines. The compound of formula CF₃CONCH₃Si(CH₃)₃ (MSTFA) is shown to exist as a tautemeric mixture of a silylamide and a silylimidate. This assignment is confirmed by ¹³C nmr. A rationale is proposed for the structure directing effect of substituents on the amide carbon atom.     

A Carbon-13 and nitrogen-15 NMR study of some nitrogen heterocycles

A number of phenyl-substituted nitrogen heterocycles and the corresponding 2,6-diethylphenyl derivatives were examined by 13 C nmr in order to verify that the heterocyclic ring system was the same in both series. The heterocyclic ring carbon shifts did not differ substantially between the phenyl and 2,6-diethylphenyl derivatives for all systems except one, where substantial differences were also seen in the ¹⁵N chemical shifts. Acetylated derivatives were prepared to confirm the cyclization mode in this latter case.     

Elucidation of the structure of quindolinone,a minor alkaloid of cryptolepis sanguinolenta: Submilligram 1H-13c and 1H-15N heteronuclear shift correlation experiments using micro inverse-detection

Elucidation of minor natural product structures has been significantly augmented by inverse-detection; further improvement has been afforded by the development of micro inverse-detection probes. We report here the elucidation of the structure of a new alkaloid, quindolinone (5H, 10H-indolo[3,2-b]quinolin-11-one), from the West African plant Cryptolepis sanguinolenta. All nmr data for this minor, preparative hplc-isolated alkaloid, including ¹H-¹⁵N one? bond heteronuclear shift correlation (HMQC) data, were recorded on an 800 μg sample of the alkaloid dissolved in 140 μl of 100% d₆-DMSO using a 400 MHz spectrometer.     

1.3-Benzodiphosphole, 1.2-bis-dimethylaminoalkylidenphosphino-benzen

The alkali phosphides of 1.2-bis-phosphinobenzene, and 1-alkyl-derivatives react with (Me₂N)₂COEt⁺BF₄^? to give the title compounds with dicoordinated phosphorus. The structure is proved by their nmr spectra.     

13C NMR investigation of tautomeric and acid-base equilibria of pyrazolone T and three analogs

Pyrazolone T and three derivatives have been characterized by ¹³C and, in part, ¹⁵N nmr at several pH values. The ¹³C chemical shifts have been assigned at, or near, the equivalence points and pK_a values of these four compounds. Closely situatued quaternary carbon signals were assigned by means of a heteronuclear chemical shift correlation (FLOCK) experiment which is sensitive to, and was optimized for, 3-bond C-H couplings. The ¹³C chemical shift data indicate the existence of both tautomeric and acid-base equilibria and demonstrate that the four congeners exist in surprisingly different forms at certain common pH values.     

The synthesis of novel polycyclic heterocyclic ring systems. 3. Synthesis and NMR spectroscopy of 15-chloro[1]benzo-thieno[2″,3″:3′,4′]naphtho[1′,2′:4,5]thieno[2,3-c]quinoline

The polycyclic heterocyclic compound with a novel ring system, 15-chloro[1]benzothieno[2″,3″:3′,4′]-naphtho[1′,2′:4,5]thieno[2,3-c]quinoline was synthesized via photocyclization of 3-chloro-N-phenyl[1]-benzothieno[2′,3′:3,4]naphtho[2,1-b]fhiophene-2-carboxamide followed by chlorination with phosphorus oxychloride. The assignment of its ¹H and ¹³C nmr spectra was accomplished by utilizing two-dimensional nmr methods.     

Ab initio study of azolides: Energetic and spectroscopic properties

We report the ab initio study of twenty‐four azolides derived from pyrrole, imidazole, pyrazole, both triazoles, tetrazole, pentazole, indole and carbazole bearing at the nitrogen atom the groups COMe, CHO, COCF₃ and CO₂Me. Theoretical values (isomerism, barriers, dipole moments, C=O stretching) are compared with experimental ones, when available, and also internally compared. A special effort has been devoted to the calculation of the absolute shieldings for the different nuclei present in azolides. At the level of calculation used (RHF/6‐311G**) the results are satisfactory. To complete the nmr data from the literature, some ¹H, ¹³C, ¹⁵N, ¹⁷O and 19F chemical shifts have been determined.