The Enantiomers of Spiro(cyclohexadiene-indolines) and their Thermal Racemization

Zimmermann, Thomas; Pustet, Nikola; Mannschreck, Albrecht

doi:10.1007/pl00010217

Cited by 3 publications

(4 citation statements)

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“…A novel class of photochromic spiroindolines, the 6-aroyl-3,5-diarylspiro(cyclohexa-2,4-diene-1,2‘-indolines) 4 , , were synthesized by the condensation of 2,4,6-triarylpyrilium salts with 2-methyleneindolines generated in situ from the corresponding 3 H -indolium salts. The intermediately formed 2 H -pyrans undergo the ring-opening reaction to their valence isomers 4b , which recyclize to give spiro(cyclohexadieneindolines) 4a .…”

Section: Spiro(cyclohexadiene-indolines)mentioning

confidence: 99%

“…The reaction shown in Scheme proceeds smoothly when refluxing ethanol or 1-butanol solutions of the components for about 2 h. An interesting feature of this transformation is its high diastereoselectivity. Although two asymmetric carbon atoms (marked in the scheme by asterisks) are created in the course of the reaction with 1,3,3-trimethyl-2-methyleneindoline (R 1 = R 2 = CH 3 ), and hence two diastereomers of 4a may be formed, only the isomers with trans configuration of the bulkier substituents (ArCO and CMe 2 ) at the C 1 (spirocarbon) and C 6 stereocenters were obtained 83a. The stereochemistry of the transformation products is not affected by the substituents in the aryl ring Ar 1 of 4 .…”

Section: Spiro(cyclohexadiene-indolines)mentioning

confidence: 99%

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Photo-, Thermo-, Solvato-, and Electrochromic Spiroheterocyclic Compounds

2004

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Section: Spiro(cyclohexadiene-indolines)mentioning

confidence: 99%

Section: Spiro(cyclohexadiene-indolines)mentioning

confidence: 99%

Photo-, Thermo-, Solvato-, and Electrochromic Spiroheterocyclic Compounds

2004

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“…Spirochromene 7 was selected to illustrate the concept of enantiomeric enrichment of stereolabile chiral compounds by dynamic (D)HPLC . Spiro(cyclohexadiene‐indolines) provided examples in which the central carbon was linked to three carbon atoms and a nitrogen . Cases in which the central carbon atom was linked to a nitrogen, an oxygen, and two carbon atoms such as in 9 were reported .…”

Section: Resultsmentioning

confidence: 99%

A Forgotten Chiral Spiro Compound Revisited: 3,3'‐Dimethyl‐3H,3'H‐2,2'‐spirobi[[1,3]benzothiazole]

et al. 2015

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The title compound was obtained as a side product during dimerization-oxidation steps of the carbene generated from N-methylbenzothiazolium iodide. Chromatography on (S,S)-Whelk O1 column showed on cooling a typical plateau shape chromatogram indicating an exchange between two enantiomers on the column. The thermal barrier to racemization was determined (85 kJ.mol(-1) at 10 °C) by dynamic high-performance liquid chromatography (DHPLC).The absolute configuration of the first (M) and second eluted (P) enantiomers on the (S, S)-Whelk O1 column was established by comparing the reconstructed circular dichroism (CD) spectra from the CD detector signal and the calculated CD spectrum of the (P) enantiomer. Mass spectrometry revealed that 3,3'-dimethyl-3H,3'H-2,2'-spirobi[[1,3]benzothiazole] can be viewed as a masked thiophenate attached to a benzothiazolium framework.

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“…Investigations on spiro[indoline-chromenes], spiro[indoline-benzoxazines] [3] and spiro[cyclohexadiene-indolines] [4] have shown that kinetic data for ring opening reactions can also be determined by liquid chromatographic separation of the enantiomers on non-racemic stationary phases followed by thermal enantiomerization, i.e. measuring the time-dependent loss of optical activity with a polarimeter.…”

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confidence: 99%

The enantiomers of 7aH-cyclopenta[b]pyran-7-ones and their thermal racemization

1999

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3952H-Pyrans are known to undergo ring opening reactions to their valence isomers, the pentadienones, which are capable to recyclize forming the starting pyrans [1,2]. These electrocyclic interconversions can be induced photochemically or by heat. In some cases an equilibrium between both isomers is observed. The favoured type of compound at given conditions strongly depends on the substitution pattern. Electron donating groups at position 5 of the pentadienone usually stabilize it by conjugation with the carbonyl group at C-1 whereas substituents at C-3 on the 2H-pyrans lead to a decrease of the tendency of electrocyclic ring opening [1,2].A possibility for the determination of kinetic data such as rate constants k or free enthalpies of activation ∆G ≠ for the electrocyclic ring opening/ring closure consists in the determination of the concentration of 2H-pyrans or pentadienones as a function of time. However, this method fails if one of the valence isomers is too stable that no formation of the other one by electrocyclic conversion can be detected. Investigations on spiro[indoline-chromenes], spiro[indoline-benzoxazines] [3] and spiro[cyclohexadiene-indolines][4] have shown that kinetic data for ring opening reactions can also be determined by liquid chromatographic separation of the enantiomers on non-racemic stationary phases followed by thermal enantiomerization, i.e. measuring the time-dependent loss of optical activity with a polarimeter.Racemic 7aH-cyclopenta[b]pyran-7-ones 1, the products of ring transformation of 2,4,6-triarylpyrylium salts with acyclic 1,2-diketones (butan-2,3-dione, 1-phenyl-propan-1,2-dione) [5] represent a novel type of 2H-pyran derivatives in which the pyran system is 2,3-anellated with a carbocyclic five-membered ring. At room temperature the isomeric cyclopentadienones 2 cannot be observed. Nevertheless, kinetic data for this interconversion should be obtained as in the case of spiro In this paper, we report such investigations and compare the data obtained with those of structurally related systems.According to the substitution pattern of the chiral center at C-7a, the 7aH-cyclopenta[b]pyran-7-ones studied can be divided into the 7a-methyl derivatives 1a-g and the compounds 1h -o bearing a phenyl group at C-7a. The separation of the enantiomers (R)-1 and (S)-1 of both types of pyrans by liquid chromatography on triacetylcellulose using methanol as eluent failed with the exception of the derivatives 1a, 1l, 1n and 1o (cf. Table 1). When the sorbent was changed to tribenzoylcellulose, an improved separation of the 7a-methyl substituted pyrans 1a -g could be observed whereas this system was inactive for the 7a-phenyl compounds 1h -o. The latter ones were successfully separated on (+)-poly(trityl methacrBarriers to ring opening were determined for two 7a-methyl and two 7a-phenyl substituted 2,4,5-triaryl derivatives by thermal racemization of the enantiomers. Substituted cyclopentadienones 2 are discussed as intermediates in the thermal electrocyclic ring opening/ring closure reacti...

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The Enantiomers of Spiro(cyclohexadiene-indolines) and their Thermal Racemization

Cited by 3 publications

References 6 publications

Photo-, Thermo-, Solvato-, and Electrochromic Spiroheterocyclic Compounds

Photo-, Thermo-, Solvato-, and Electrochromic Spiroheterocyclic Compounds

A Forgotten Chiral Spiro Compound Revisited: 3,3'‐Dimethyl‐3H,3'H‐2,2'‐spirobi[[1,3]benzothiazole]

The enantiomers of 7aH-cyclopenta[b]pyran-7-ones and their thermal racemization

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