Chiral Crystallization: Freezing a Rapid Cope Rearrangement in the Solid State

Siegwarth, Jan; Bornhöft, Jan; Näther, Christian; Herges, Rainer

doi:10.1021/ol901326p

Cited by 19 publications

(9 citation statements)

References 32 publications

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“…[1] To resolve optically active materials by crystallization efficiently, dynamic preferential crystallization involving a racemization process, a so-called total spontaneous resolution, has been developed. [5][6][7] We have now developed a new example of total spontaneous resolution of isoindolinones that involves a combination of an intramolecular equilibrium reaction via an achiral intermediate and preferential crystallization.Various heterocyclic compounds containing the isoindolinone skeleton have important biological activities, and many of these have been prepared and examined as pharmaceutical agents. [5][6][7] We have now developed a new example of total spontaneous resolution of isoindolinones that involves a combination of an intramolecular equilibrium reaction via an achiral intermediate and preferential crystallization.…”

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Total Spontaneous Resolution by Deracemization of Isoindolinones

et al. 2012

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Separated: 3-hydroxy-3-phenylisoindolin-1-ones have been resolved by dynamic preferential crystallization. The compounds were effectively racemized through ring-opening and ring-closing reactions via achiral intermediates under basic conditions. Crystallization from a toluene solution containing 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with stirring and evaporation of the solvent gave optically active crystals quantitatively with high ee values.

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Total Spontaneous Resolution by Deracemization of Isoindolinones

et al. 2012

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“…NMR spectroscopy showed a similar geometrical preference in solution. The bridging hydrogen fluctuates between the two chromophores in solution, and this fluctuation is reduced at low temperature and completely suppressed in the crystal [23]. The energy barrier for the H shift is linearly correlated with the C⋅⋅⋅C + distance (D) determined by X-ray.…”

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confidence: 99%

Intramolecular triarylmethane-triarylmethylium complex: Generation, properties, and X-ray structure of a C–H bridged carbocation

Suzuki

Takeda

Yoshimoto

et al. 2010

Pure and Applied Chemistry

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A series of title carbocations was generated and isolated as stable salts. X-ray analyses revealed a preference for an unsymmetric structure in which the bridging hydrogen is localized on one of the two triarylmethane units. NMR spectroscopy showed a similar preference in solution. The bridging hydrogen fluctuates between the two chromophores in solution, and the energy barrier for the H shift is linearly correlated with the C⋅⋅⋅C + separation determined by X-ray. According to an extrapolation, the energy barrier should decrease when the C⋅⋅⋅C + separation is less than 2.7 Å, which suggests a new model for isolable pure organic species with a three-center-two-electron bond. theme of aromaticity. ‡ Corresponding author [2f,4b]. Thus, we were interested in the novel properties or reactivities associated with the cleavage of a polyarylated C-C bond.Several years ago, we encountered an intriguing case: a long C-C bond was cleaved by a Brønsted acid when 1,2,2-tris(4-dimethylaminophenyl)-(3a) or 1-phenyl-2,2-bis(4-dimethylaminophenyl)-1acenaphthenol (3b) [1.648(4) Å] was treated with HBF 4 [8]. The products were not the expected 1,2,2triaryl-1-acenaphthenyliums [9], but rather 8-aroyl-1-naphthylbis(4-dimethylaminophenyl)carbeniums 4a,b + where the acid-induced oxidative protonolysis of the long C-C bond accompanied by formal hydride abstraction (Scheme 2). Ketocarbeniums 4a,b + were also obtained as triiodide salts upon the oxidation of 3a,b with 3 equiv of iodine.Compared to the protonolysis of a C-H bond [10], C-C cleavage is less common under acidic conditions [11]. As one of the plausible reaction mechanisms, we assumed direct protonation of the long C-C sigma bond with hydrogen-bridged carbeniums 5a,b + as the key intermediates in the oxida-T. SUZUKI et al.Scheme 1 1,1,2,2-Tetraarylacenaphthenes 1 and 9,9,10,10-tetraaryl-9,10-dihydrophenanthrenes 2 are representative dynamic redox systems, which undergo reversible cleavage/formation of the long C-C bond [1.614(2)-1.771(3) Å] with redox reactions. The dicationic dyes can be isolated as stable salts to exhibit electrochromic response.Scheme 2 Upon treatment of 1,2,2-triaryl-1-acenaphthenols 3a,b, the products were not the expected 1,2,2-triaryl-1-acenaphthenyliums but ketocarbeniums 4a,b + . Thus, the acid induced oxidative protonolysis of the long C-C bond [3b: 1.648(4) Å], which is less common compared to the protonolysis of a C-H bond. tive protonolysis of 3a,b (Scheme 3). The structurally related tetraaryl species 6c + (Ar = 4-MeOC 6 H 4 ) with a three-center geometry was later postulated as a possible intermediate in the oxidative protonolysis of 1,1,2,2-tetraanisylacenaphthene 1c by Gabbaï and a co-worker (Scheme 4), and this was thought be unstable under the acidic reaction conditions and spontaneously transformed into dication 1c 2+ [12]. However, we formed a different opinion based on our results with (8-diarylmethyl-1-naphthyl)bis(4dimethylaminophenyl)carbeniums 6d-f + (X = OMe, H, I), which were generated from the carbinol precursors upon treatment with ...

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“…Substrates 14 and 15 , which feature pendant olefins, underwent cycloisomerization with the cationic gold catalyst 11 to form barbaralanes 16 / 16′ and 17 , respectively. The tautomeric barbaralanes 16 and 16′ interconvert rapidly on the NMR timescale at room temperature in CDCl 3 through a strain‐assisted Cope rearrangement22 and were detected as a 1:1 mixture in the crystal state,23, 24 whereas 17 was observed as a single tautomer 24…”

Section: Screening Of Gold and Other Lewis Acid Catalysts[a]mentioning

confidence: 99%

Gold for the Generation and Control of Fluxional Barbaralyl Cations

et al. 2012

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Das „formwandlerische“ Barbaralyl‐Kation existiert als Gemisch von 181 400 entarteten Formen. Es ergab sich, dass Gold‐katalysierte Cycloisomerisierungen von 7‐Alkinylcyclohepta‐1,3,5‐trienen über fluxionale Barbaralyl‐Zwischenstufen verlaufen (siehe Schema). Die Evolution der Zwischenstufen in 1‐ oder 2‐substituierte Indene ließ sich durch die Wahl des Goldkomplexes steuern.

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Chiral Crystallization: Freezing a Rapid Cope Rearrangement in the Solid State

Cited by 19 publications

References 32 publications

Total Spontaneous Resolution by Deracemization of Isoindolinones

Total Spontaneous Resolution by Deracemization of Isoindolinones

Intramolecular triarylmethane-triarylmethylium complex: Generation, properties, and X-ray structure of a C–H bridged carbocation

Gold for the Generation and Control of Fluxional Barbaralyl Cations

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