Circular dichroism spectra and molecular geometry of six-membered ring anhydrides and imides

Połoński, Tadeusz

doi:10.1039/p19880000639

Cited by 21 publications

(6 citation statements)

References 3 publications

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“…The precursor (6a) was obtained from (S)-2-benzyloxycarbonylglutamine in three steps (Scheme 3). The starting material was cyclised using thionyl chloride, 10 and hydrogenated. 11 The resulting amine hydrochloride (5a) was then treated with 2-bromobenzoyl chloride and sodium carbonate to obtain 6a.…”

Section: Resultsmentioning

confidence: 99%

[11C]/(13C)Carbon monoxide in palladium-mediated synthesis of imides

Karimi

Kihlberg

Långström

2001

J. Chem. Soc., Perkin Trans. 1

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published as an Advance Article on the web 5th June 2001 [ 11 C]Carbon monoxide in low concentration with palladium(0) complexes (in the range of 5 µmol) and aryl halides (about 10 µmol) were used in the synthesis of the 11 C-labelled imides, thalidomide, N-phthaloyl--glutamic acid, N-phthaloylhexane and aniracetam. The labellings were performed with ring closure reactions except in the case of aniracetam. These imides were obtained in nearly quantitative radiochemical yields, calculated from the [ 11 C]carbon monoxide, with specific radioactivities between 70-600 GBq µmol Ϫ1 . The radiochemical purity of the LC-purified products exceeded 98%. N-( 13 C)Phthaloyl--glutamic acid 2 was produced to verify the position of the label (δ 167.5 ppm) with 13 C NMR, and this also indicates that the discussed approach is valuable for labelling with other carbon isotopes. In a typical experiment starting with 2.8 GBq of [ 11 C]carbon monoxide, 0.6 GBq of HPLC-purified [ 11 C]-N-phthaloyl--glutamic acid 2 was obtained within 40 minutes from the start of the carbonylation reaction (84% decay-corrected radiochemical yield).

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Section: Resultsmentioning

confidence: 99%

[11C]/(13C)Carbon monoxide in palladium-mediated synthesis of imides

Karimi

Kihlberg

Långström

2001

J. Chem. Soc., Perkin Trans. 1

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“…Several rules relating the signs of particular CEs from the n−π* region with the geometry of imides have been proposed. − Połoński proposed a general rule for anhydrides and imides: the antioctant rule for the lowest n−π* excitation and the octant rule for the next n−π* transition . To the best of our knowledge, all previously investigated imides are cyclic whereas compounds 13 − 21 contain one of the carbonyl groups of the imide chromophore outside the ring frame.…”

Section: Resultsmentioning

confidence: 99%

Configurational Assignment of 5-Substituted Pyrazolidin-3-ones Using Circular Dichroism Spectroscopy

et al. 1999

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The chiroptical properties of the title compounds bearing various substituents at the N(1) and N(2) nitrogen atoms are discussed. It was found that the sign of the n−π* Cotton effect centered at about the 230−250 nm region can be correlated with the absolute configuration of the stereogenic center at C(5). It was also found that the sign of this Cotton effect is predictable by Weigang's lactam sector rule. MMX calculations, supported by X-ray measurements, showed that substituents at the nitrogen atoms significantly affect the conformation of the five-membered ring. It was additionally concluded that the conformation of the five-membered ring in 5-substituted pyrazolidin-3-ones is the sign-determining factor for an n−π* transition.

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“…All spectroscopic measurements were carried out as described previously 2b. The synthesis of compound 1 has been published elsewhere …”

Section: Methodsmentioning

confidence: 99%

“…The structure, electronic absorption spectra, and chiroptical properties of imides have been a subject of considerable interest in recent years. , These compounds show two weak n−π* absorption bands followed by a moderately intense π−π* transition in the region of 270−200 nm as predicted by semiempirical MO calculations. 2a,c It is well known that the substitution of sulfur for oxygen in the carbonyl group shifts absorption maxima to much longer wavelengths . This allows observation of the lowest energy excited states of thiocarbonyls at the visible or near-UV region.…”

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Chiroptical Spectra of 1,2-Cyclopropanedicarboxylic Monothioimides¹

1997

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The structure, electronic absorption spectra, and chiroptical properties of imides have been a subject of considerable interest in recent years. 2,3 These compounds show two weak n-π* absorption bands followed by a moderately intense π-π* transition in the region of 270-200 nm as predicted by semiempirical MO calculations. 2a,c It is well known that the substitution of sulfur for oxygen in the carbonyl group shifts absorption maxima to much longer wavelengths. 4 This allows observation of the lowest energy excited states of thiocarbonyls at the visible or near-UV region. There are some reports on the electronic and circular dichroism (CD) spectra of dithioimides, 5,6 but much less is known on the spectroscopic properties of monothioimides. 6 In this paper, we describe the electronic and chiroptical spectra of cis-1,2-cyclopropanedicarboxylic monothioimides 1-4. Their bicyclic skeleton is relatively rigid due to steric constraints imposed by the cyclopropane ring, and thus, the influence of conformational effects on the CD spectra should be negligible. By analogy with the parent imides, the geometries of which are known from the X-ray structures, 3,7 the 3-azabicyclo[3.1.0]hexane moiety in 1-4 is expected to adopt a sofa-like (half-boat) conformation with the -carbon atom being out of the plane formed by the remaining ring atoms. For comparison, we prepared and measured the CD of the related monocyclic thioimide 5, for which much more conformational freedom was expected. Its geometry in the solid state was established by X-ray crystallography. Results and DiscussionThe synthesis of the compound 1 with chirality solely due to the sulfur substitution has been described earlier. 8 Thioimides 2-5 were obtained by thionation of corresponding imides of the known absolute configuration 3 with Lawesson's reagent. 9 Owing to a steric effect of the R-substituent, the reaction occurs at the less hindered carbonyl to give single isomers 3-5. Only in the case of 2 was the reaction product contaminated with a small amount of the second isomer and purified by fractional crystallization. Small quantities of the corresponding dithioimides formed during the thionation can be readily separated by column chromatography in the workup procedure.The UV-vis spectrum of the thioimide 1 in cyclohexane contains two weak absorption bands appearing as a maximum at 408 nm ( 46) and a shoulder at 326 nm (97), in addition to a strong absorption at 274 nm (18 000), shifting in methanol to 400, 320, and 276 nm, respectively. In the six-membered ring compound 5 the analogous UV bands are shifted to slightly longer wavelengths (Table 1). A similar observation concerning the electronic spectra of thiosuccinimide and thioglutarimide has been described by Berg and Sandström. 6 The intensity of the observed absorptions and the solvent effects suggest the n-π* character of two lowest energy transitions and the π-π* nature of the strong absorption at the shorter wavelengths. The shape of the molecular orbitals involved in these transitions was est...

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Circular dichroism spectra and molecular geometry of six-membered ring anhydrides and imides

Cited by 21 publications

References 3 publications

[11C]/(13C)Carbon monoxide in palladium-mediated synthesis of imides

[11C]/(13C)Carbon monoxide in palladium-mediated synthesis of imides

Configurational Assignment of 5-Substituted Pyrazolidin-3-ones Using Circular Dichroism Spectroscopy

Chiroptical Spectra of 1,2-Cyclopropanedicarboxylic Monothioimides¹

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Circular dichroism spectra and molecular geometry of six-membered ring anhydrides and imides

Cited by 21 publications

References 3 publications

[11C]/(13C)Carbon monoxide in palladium-mediated synthesis of imides

[11C]/(13C)Carbon monoxide in palladium-mediated synthesis of imides

Configurational Assignment of 5-Substituted Pyrazolidin-3-ones Using Circular Dichroism Spectroscopy

Chiroptical Spectra of 1,2-Cyclopropanedicarboxylic Monothioimides1

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Chiroptical Spectra of 1,2-Cyclopropanedicarboxylic Monothioimides¹