Nuclear magnetic resonance spectra of some 2,6-disubstituted spiro[3.3]heptane derivatives

Analysis of the full splitting pattern of the 100 MHz ¹H-NMR spectra of diethyl - 2,6 -dibromospiro[3.3]heptane - 2,6 - dicarboxylate (3) in chloroform and benzene and the 220 MHz ¹H-NMR spectrum of dimethylspiro[3.3]heptane - 2,6 - dicarboxylate (2) in naphthalene has been carried out. Puckering of the cyclobutane rings is revealed. Reasonable agreement with an X-ray study on Fecht acid (1) and with the data from the ¹C-NMR spectra of compounds 2 and 3 has been obtained. The temperature dependency of the ¹H-NMR spectra of 2, 3 and the symmetrically substituted tetraethylspiro[3.3]heptane - 2,2,6,6 - tetracarboxylate (4) has been investigated and is discussed in terms of conformational interconversion.     

Synthesis and characterization of a new pillar[5]arene-based [1]rotaxane

In this study, we reported the synthesis of three kinds of mono-functional pillar[5]arene derivatives PRI, PRII and R and their structures were studied by 1D and 2D NMR spectra and mass spectra. The 2D NMR spectra including ¹H-¹³C HSQC, ¹H-¹H COSY and NOESY spectra indicated that PRI and PRII are both stable self-included pseudo[1]rotaxanes in CDCl₃. These original structures are promising compounds for the design of pillar[5]-based [1]rotaxane. And the results showed that R could exist stable in CDCl₃ and DMSO because of the coordination of N-H?O hydrogen bonding interaction and C-H?π interaction.     

Structure and spectral properties of two novel isomeric 2,4-dimethyl- 2-methoxy-3,8-dioxabicyclo [3.2.1] octanes

The preparation and structure of the novel bicyclic ketals 5 and 6 is reported. A single crystal X-ray structure of compound 5 establishes the structures of 5 and 6. ¹H and ¹³C NMR spectra are interpreted in terms of chair conformations for both 5 and 6, even though an unfavorable syn-diaxial interaction is present in 6. In the ¹H spectra, the axial C-4 proton of compound 5 absorbs downfield of its equatorial counterpart in 6. This is apparently due to a deshielding effect of the syn-diaxial C-2 methoxy group in compound 5.     

Synthesis,spectral and computational studies of some N-acyl-t(3)-isopropyl-r(2),c(6)-bis-2′-furylpiperidin-4-one oximes

Four N-acyl-t(3)-isopropyl-r(2),c(6)-bis-2′-furylpiperidin-4-one oximes 1–4 were synthesized and the high resolution ¹H and ¹³C NMR spectra have been recorded at various temperatures and analyzed. The spectra reveal the presence of two rotameric forms (syn and anti) in solution. ¹H-¹H COSY and ¹H-¹³C COSY spectra have been recorded to assist the assignment of the signals for the syn and anti isomers of 1–4. Coupling constants predict an equilibrium mixture of boat form B₁ and alternate chair form CA for 1–4. The effect of varying the substituents at nitrogen and at C(4) on the ¹H and ¹³C chemical shifts has been analyzed in detail. The molecular structures of the N-acyl derivatives 1–4 were also determined using AM1 Hamiltonian and the results have been compared to the results derived from spectral studies. Mass spectra have also been recorded for 1–4.     

Rearrangement thermique des adduits du tetracyanoethylene de 2H-pyrannes

The addition of tetracyanotehylene to 2H-pyrans 1 results in a mixture of two isomeric adducts 6. The thermal decomposition of the compounds 6 gives rise to both a small percentage of the retro Diels-Alder, and a new mode of evolution leading to a mixture of furans (E+Z) 7. A detailed interpretation of the ¹³C spectra of the compounds 7 was established by comparison with the ¹³C spectra of 2,5-diphenylfuran and trans-stilbene. The structure 7 is confirmed by chemical degradation.     

Preparation and spectra of mercuribis (α-diazo ketones)

Bis (α - diazophenacyl) mercury (2a), bis (α - diazo - 2,4,6 - trimethylphenacyl) mercury (2b), bis (1 - diazo - 3,3 - dimethyl - 2 - oxobutyl)mercury (2c), and bis (1 - diazo - 2 - phenylacetonyl) mercury (2d) have been prepared by treatment of the corresponding α-diazo ketones with mercuric oxide. The solution IR, UV, and ¹H NMR spectra of 2a–d and of three other mercuribis (α-diazo ketones) have been compared with the spectra of the corresponding α-diazo ketones, and the similarities between these have led to the conclusion that in solution these mercury derivatives exist with the mercury bonded to carbon. The ¹³C NMR resonance spectra of 2a and of α-diazo - α - methylmercuriacetophenone (9) have been examined for evidence of ¹⁹⁹HgC coupling; this was observed in the case of 9 for the Me carbon, but not detected in either case for the diazo carbon; this is attributed to difficulty of detection and/or ligand exchange. The signals of the diazo carbon in these spectra occur at unusually high field; a similar observation was made in the spectra of several α-diazo ketones, where the chemical shifts were in the range δ 50–70.     

Conformational analysis of methylsuccinic acid by 1H NMR spectroscopy and circular dichroism

The pH-dependence of the ¹H NMR and Circular Dichroism (CD) spectra of 2-methylsuccinic acid was investigated. Both spectra undergo dramatic changes between pH 4 and 6, where both carboxylic groups become ionized. From the coupling constants of the tertiary proton with the assigned¹ diastereotopic methylene protons, it is concluded that below pH 4 the syn-clinal (2) and above pH 6 the anti-periplanar (1) conformation of methylsuccinic acid prevail. The diesters of methylsuccinic acid also assume mainly the syn-clinal conformation (2). The pH-dependence of the CD spectra is discussed in terms of conformation and/or ionization effects.     

Enantioselective recognition by optically active chiral fluorescence sensors bearing amino acid units

Chiral fluorescence receptors 1 and 2 were synthesized and their structures characterized by IR, ¹H NMR, ¹³C NMR, MS spectra, and elemental analysis. The chiral recognition abilities of 1 and 2 were studied by ¹H NMR and fluorescence spectra. The results demonstrate that receptors 1 and 2 with bis(tetrabutylammonium) dibenzoyl tartrate formed a 1:1 complex. Receptor 2 exhibits an excellent enantioselective recognition ability toward the enantiomers of bis(tetrabutylammonium) dibenzoyl tartrate.     

The stereochemistry of 2,4-disubstituted γ-butyrolactones and 2,4,6-trisubstituted-5,6-dihydro-4H-1, 3-oxazines

2,4-Disubstituted butyrolactones and 2,4,6-trisubstituted-5,6 dihydro-4H-1,3-oxazines show similar features in their ¹H and ¹³C- NMR spectra. Two geminal ring hydrogens of cis isomers give rise to a complex ABXY spectra when the substituent is alkyl or aryl. In spectra of trans isomers these patterns are degenerated. When R is OMe(in 4) or OCOMe (in 6) the difference in chemical shifts of geminal protons and vicinal coupling constants cannot be used for diagnosis. In ¹³C spectra ring carbons C-2 and C-3 in lactones and C-4 and C-5 in oxazine of trans isomers show a small but consistent shift to higher fields.     

Stereoselective approach to uncommon tripeptides incorporating a 2,6-diaminopimelic acid framework: X-ray analysis and conformational studies. Part 4

Stereoselective synthesis of pseudopeptides 4, 5, 8, 9, 13 and 14, incorporating 2,6-diamino-4-methylen-1,7-heptanedioic acid residue, has been accomplished starting from the l-valine derived chiral synthon 1. The absolute configuration of new stereocentres was assigned on the basis of ¹H NMR spectra. The geometry of these unnatural tripeptides was deduced on the basis of ¹H NMR parameters and IR spectra. X-ray analysis of the unusual peptide 18 and conformational studies of 5, 9 and 14 are also reported.     

Azapropellanes as phase-transfer catalysts—II: A CMR and PMR study of the three-dimensional structure of 1-azoniapropellanes containing 5- and 6-membered rings

An improved synthesis of 1-azoniatricyclo[4.4.3.0^1,6]tridecane (2) and the preparation of the remaining member of the series, 1-azoniatricyclo[4.3.3.0^1,6]dodecane salts (3) have been achieved. Using a combination of ¹H (at 400 MHz) and ¹³C NMR spectra has allowed the assignment of the signals in the well-resolved ¹H spectra. The results indicate that 1 exists in the all-chair form which undergoes racemization by ring inversion with a rate constant of 0.7 sec^? and further that the counterion in these salts is restricted to associating with only one face of the tetrahedral N atom.     

Enamine chemistry—XXII: The preparation of 4-acylaminopent-3-en-2-ones and the corresponding enamino-thiones

Acylation of 4-aminopcnl-3-en-2-one, 5, with different acid chlorides, RCOCl(R = Me, Me₂CH, Me₃C, C₆H₅, CICH₂) gives only N-acylated products, 6, in high yields. The N-acylated enaminones, 5, are shown only to exist m the Z-s-Z form in solution. The UV spectra of 6 are discussed and an additional increment to the Dabrowski-Table²¹ is given. The reaction of 6 with 2,4-bis(4-methoxyphenyl)-1,2,3,4-dithiadiphosphetane 2,4-disulfide, 2, at room temperature in DME gives the corresponding enamino-thiones, 7, in good yields. The ¹H and ¹³C NMR spectra of 6 and 7 are discussed.     

Cyclophanes with large internal substituents. The synthesis and conformational behavior of 2,11-dithia [3,3]metacyclophanes and a [2,2] metacylophane with tert-butyl substituents.

The preparation, ¹Hmr spectra and stereochemistry of 1E , 3E , 2F ,3F and 2G are described. The stereochemistry of 3E is supported by an X-ray structure determination.     

13C-NMR-spektren von spiro[2.4]hepta-(1,4,6)-trienen und -(4.6)-dienen

The ¹³C NMR spectra of [1.2]-spirenes 2 and spiro[2.4]hepta-(4.6)-dienes 5 are described and the effects of substituents are discussed. A bonding model of the [1.2]-spirenes 2 is derived on the basis of C-H coupling constants and calculated charge densities. The ¹³C NMR shifts of 1-aryl-spiro[2.4]hepta-(4.6)-dienes 6 show a good correlation with the Hammett σp constants of the substituents in p-position of the phenyl ring. Conclusions on spiroconjugation in [1.2]-spirenes 2 are drawn from comparing the ¹³C shifts of similar substituted [1.2]-spirenes and spiro[2.4]hepta-(4.6)-dienes. The spiroconjugation in [1.2]-, [2.2]- and [2.3]-spirenes 2, 3 and 4 is discussed comparing the calculated charge densities with the δ (¹³C) values, as well as the UV and p.e. spectra.     

A novel fluorescence sensor for K+ based on bis-Bodipy: The ACQ effect controlled by cation complexation of pseudo crown ether ring

Three novel bis-Bodipy 3a–3c bridged with crown ether chain were prepared in yields of 70–78%. Their complexation absorption and fluorescent spectra for fourteen metal ions suggested that compound 3b exhibited the selective response for K⁺ with obvious ACQ effect. The association constant of compound 3b with K⁺ was 4.3 × 10⁵ M^?1 and 1:1 complex mode was deduced. The complexation mechanism of ACQ effect controlled by cation complexation of pseudo crown ether ring was confirmed by the fluorescent titrations, complexation FT-IR spectra, complexation ¹H NMR spectra, complexation ESI-MS spectra and contrast experiment of similar mono-Bodipy derivative. The K⁺ was binded in the cavity of a pseudo crown ether ring, leading to the closed distance for two Bodipy units and then enhancing the ACQ effect obviously. Both the structure of the crown ether chain and two Bodipy units were decisive factors for the selective fluorescence sensor for K⁺.     

Synthesis and conformational analysis of 1,3-azasilinanes

1-Isopropyl-3-methyl-3-phenyl-1,3-azasilinane 1 and 1-isopropyl-3,3-dimethyl-1,3-azasilinane 2 were synthesized and a detailed analysis of their NMR spectra, conformational equilibria and ring inversion processes is presented. Low temperature ¹H/¹³C NMR spectroscopy, iteration of the ¹H NMR spectra and quantum chemical calculations showed slight predominance of the Ph_eqMe_ax over the Ph_axMe_eq conformer of 1 at low temperature. The barrier for the chair to chair interconversion of both compounds was measured to be 8.25 kcal/mol.     

Synthesis and conformational analysis of some cyanomethylene derivatives of piperidines

Five 4-dicyanomethylene derivatives 6–10, N-cyanoacetyl-cis-2,6-diphenylpiperidin-4-one 11 and 4-cyano(ethoxycarbonyl)-methylene-cis-2,6-bis(o-chlorophenyl)piperidine 12 were synthesised by condensing the appropriate piperidin-4-ones 13–17 with malononitrile/ethylcyanoacetate and their ¹H and ¹³C NMR spectra were recorded. The ¹H-¹H COSY spectrum for 6 and NOESY spectra for 8, 10, and 11 were also recorded. Based on coupling constants and the results obtained from NOESY spectra boat conformation for 10 and epimerised chair conformations for 8 and 9 have been proposed. Other derivatives adopt normal chair conformations. Theoretical calculations and the ¹H and ¹³C chemical shifts also support the above conformations. Mass spectra were also recorded for 6–12.     

Synthesis and chiral recognition of novel chiral fluorescence receptors bearing 9-anthryl moieties

Two chiral fluorescence receptors 1 and 2 have been synthesized, and their structures characterized by IR, ¹H NMR, MS spectra and elemental analysis. The chiral recognition of the receptors was studied by ¹H NMR and fluorescence spectra. The results demonstrate that the receptors and tetrabutylammonium mandelate formed a 1:1 complex. Two receptors exhibit good chiral recognition abilities towards the enantiomers of tetrabutylammonium mandelate.     

The orthosomycin family of antibiotics-II : The13C NMR spectra of flambamycin and its derivatives

The important features of the ¹³C NMR spectra of flambamycin (1a) and its degradation products (22–12) are discussed, and assignments are made. The general use of ¹³C NMR spectroscopy for structural investigations of the orthosomycin family of antibiotics is summarised.     

Oxo transfer reaction: Dioxido and monooxidovanadium(V) complexes

A dioxidovanadium(V) complex of type [(L_ONOH^?)(VO₂)] (1) was isolated where L_ONOH₂ is a tridentate ONO donor benzhydrazide ligand. 1 undergoes an oxo transfer reaction with triphenylphosphine in presence of 8-hydroxyquinoline (HQ) and affords a monooxidovanadium(V) complex of type [(L_ONO^2?)(VO)(Q^?)] (2). 1 and 2 were substantiated by elemental analyses, ESI-mass, IR, ¹H NMR, ⁵¹V NMR and UV–vis spectra. The molecular geometries of 1 and 2 were authenticated by single crystal X?ray crystallography. UV–vis absorption spectra of 1 and 2 display bands respectively at 325 and 320 nm due to oxido → vanadium(V) charge transfer transitions. 1 exhibit an irreversible cathodic peak at ?0.44 V whereas 2 displays a reversible cathodic wave at ?0.60 V in cyclic voltammogram due to the VO³⁺/VO²⁺ redox couple.