High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals

Chmielewski, Marek; Kałuża, Zbigniew; Bełżecki, C.; Salanski, P.; Jurczak, Janusz; Adamowicz, Halina

doi:10.1016/s0040-4020(01)96639-6

Cited by 35 publications

(4 citation statements)

References 11 publications

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“…Some authors classified the reaction with TS nonplanarity of ca. 30° as pseudopericyclic . Here, we arbitrarily accept the TS nonplanarity from −45° to +45° for the reaction to be classified as pseudopericyclic, and thus, NP-pseudopericyclic is the reaction with discontinuity and ring nonplanarity exceeding 45°.…”

Section: Resultsmentioning

confidence: 99%

“…30°as pseudopericyclic. 22 Here, we arbitrarily accept the TS nonplanarity from -45°t o +45°for the reaction to be classified as pseudopericyclic, and thus, NP-pseudopericyclic is the reaction with discontinuity and ring nonplanarity exceeding 45°. Last but not least, in two cases (namely, TS B (9,10) and TS B ( 14)), the new BCP and RCP indicate hydrogen-bond-like interaction 63 in the TS rather than σ-bond formation.…”

Section: Resultsmentioning

confidence: 99%

“…For example, the existence of an intermediate, 19 the classical Woodward-Hoffmann supraantra, 20 and pseudoconcerted mechanisms were proposed. 21,22 The mechanism of the allene-isocyanic acid reaction, leading to 3-methylene-β-lactam, was investigated by Cossio et al at the HF/6-31G* and MP2/6-31G* levels. 23 The transition-state (TS) structures found were planar and corresponded to a concerted (one-step), yet asynchronous mechanism, namely, [ π 2 s + π 2 a ].…”

Section: Introductionmentioning

confidence: 99%

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An ab Initio Study on the Allene−Isocyanic Acid and Ketene−Vinylimine [2 + 2] Cycloaddition Reaction Paths

Rode

Dobrowolski

2006

J. Phys. Chem. A

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The reaction paths of [2 + 2] cycloadditions of allene (H2C=C=CH2) to isocyanic acid (HN=C=O) and ketene (H2C=C=O) to vinylimine (H2C=C=NH), leading to all the possible 14 four-membered ring molecules, were investigated by the MP2/aug-cc-pVDZ method. In the two considered reactions, the 2-azetidinone (beta-lactam) ring compounds were predicted to be the most stable thermodynamically in the absence of an environment. Although 4-methylene-2-azetidinone is the most stable product of the ketene-vinylimine cycloaddition, its activation barrier is higher than that for 4-methylene-2-iminooxetane by ca. 6 kcal/mol. Therefore, the latter product can be obtained owing to kinetic control. The activation barriers in the allene-isocyanic acid reactions are quite high, 50-70 kcal/mol, whereas in the course of the ketene-vinylimine cycloaddition they are equal to ca. 30-55 kcal/mol. All the reactions studied were found to be concerted and mostly asynchronous. Simulation of the solvent environment (toluene, tetrahydrofuran, acetonitrile, and water) by using Tomasi's polarized continuum model with the integral equation formalism (IEF-PCM) method showed the allene-isocyanic reactions remained concerted, yet the activation barriers were somewhat higher than those in the gas phase, whereas the ketene-vinylimine reactions became stepwise. The larger the solvent dielectric constant, the lower the activation barriers found. The lowest-energy pathways in the gas phase and in solvent were confirmed by intrinsic reaction coordinate (IRC) calculations. The atoms in molecules (AIM) analysis of the electron density distribution in the transition-state (TS) structures allowed us to distinguish pericyclic from pseudopericyclic from nonplanar-pseudopericyclic types of reactions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An ab Initio Study on the Allene−Isocyanic Acid and Ketene−Vinylimine [2 + 2] Cycloaddition Reaction Paths

Rode

Dobrowolski

2006

J. Phys. Chem. A

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“…On this basis, we envisaged that lower temperatures, shorter reaction times, and use of a lower excess of the reacting glycal might be involved if the same cycloadditions were carried out under high pressure conditions. 6,7 Thus, the two acyclic nitrones 5 and 6 and the enantiopure substituted pyrroline N-oxides 7, 8, and 9, derived from D-tartaric, L-malic, and Ltartaric acids, respectively, 8 were treated under high pressure with protected glycals 10-15, prepared from D-glucose, D-galactose, Lrhamnose, and D-arabinose. All experiments were carried out according to standard procedures; 9 the obtained results are summarized in Table 1.…”

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confidence: 99%

Remarkable High-pressure Enhancement of Enantiopure Nitrone Cycloadditions to Glycals: General Access to (1 → 2)-Linked Pseudo Aza-C-disaccharides

Cardona¹,

Salanski²,

Chmielewski³

et al. 1998

Synlett

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1,3-Dipolar cycloadditions of enantiopure hydroxylated nitrones to glycals are strongly accelerated under high pressure. Under 10 Kbar pressure the process gains generality and broad scope and allows a direct access, in good to excellent yields, to stereodifferentiated tricyclic isoxazolidines, key intermediates for the synthesis of a new class of (1→2)-linked pseudo aza-C-disaccharides.The growing interest for the synthesis of aza-C-disaccharides is connected to the need for new selective glycosidase inhibitors. 1 It is indeed generally thought that stable imino-C-disaccharides, in which a sugar is linked to an iminosugar (azasugar) through a carbon bond, should mimic both the glycosyl and the aglycon during the glycosidic process, and therefore should be more selective glycosidase inhibitors. 2 In this context, we have recently reported a straightforward synthesis of a broad new class of (1→2)-linked pseudo aza-C-disaccharides 1 possessing the sugar portion directly linked to C(1) of an imino sugar, by means of the novel cycloaddition of enantiopure cyclic nitrones 3 to glycals 4. 3This new approach is extremely advantageous, being the most direct pathway to the pseudo aza-C-disaccharide skeleton and allowing its synthesis in only a few steps. The major limitation consists in the low reactivity of nitrones towards glycals in the crucial cycloaddition step. Reasonable yields (higher than 50%) were obtained only for the most stable nitrones 7 and 8 with triacetyl glucal (entries c-d, Table 1) forcing the reaction conditions (100 °C, long reaction times, use of an excess of glycal, Table 1). Under these conditions, the stability of the nitrone and the glycal employed becomes crucial.It is well established that the use of high pressure accelerates the rate of reactions characterized by a negative volume of activation, such as cycloaddition reactions. 4 The volume of activation for 1,3-dipolar cycloadditions (-18 to -24 cm 3 mol -1 ) 5 holds for significant increase of the reaction rate under high pressure. On this basis, we envisaged that lower temperatures, shorter reaction times, and use of a lower excess of the reacting glycal might be involved if the same cycloadditions were carried out under high pressure conditions. 6,7 Thus, the two acyclic nitrones 5 and 6 and the enantiopure substituted pyrroline N-oxides 7, 8, and 9, derived from D-tartaric, L-malic, and Ltartaric acids, respectively, 8 were treated under high pressure with protected glycals 10-15, prepared from D-glucose, D-galactose, Lrhamnose, and D-arabinose. All experiments were carried out according to standard procedures; 9 the obtained results are summarized in Table 1.The experiments were performed in toluene (0.24 M) 10 at 60 °C for 3 days under 10 Kbar pressure and using only 2 eq of glycal; the unreacted glycal can be recovered after FCC (Flash Column Chromatography) of the crude reaction mixtures. The acyclic nitrone 5 did not afford any product even under high pressure, denoting that the Downloaded by: National University of Singapore. Co...

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Chirale Cyclobutanone durch [2 + 2]‐Cycloaddition von Dichlorketen an Kohlenhydratenolether

1989

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Der stereochemische Verlauf der Dichlorketenaddition an die Kohlenhydratenolether ist bei 1 a, b und 8a, b einheitlich, bei einer durch den Enolether festgelegten Regiochemie entsteht jeweils nur eines der beiden moglichen Diastereomere. Erscheint die Umsetzung der beiden Glycale 1 a, b zu den ,,a-orientierten" Produkten 2a, b als plausibel, so ist die In-terpretation der Befunde fur die Umsetzungen von 4a, b, 8 a, b und 11 schwieriger. Umfangreiches Vergleichsmaterial aus der Kohlenhydratchemie belegt, daR sp3-und sp2-hybridisierte Kohlenstoffatome an den Positionen 3 und 4 von Derivaten der 1,2;5,6-Di-O-isopropyliden-a-~-glucofuranose praktisch immer von oberhalb der Zuckerringebene (der p-Seite) angegriffen werden, und zwar unabhangig vom verwendeten Reagens. Im Gegensatz hierzu ist bei 4 a (R,R = Isopropyliden) der Angriff von der a-Seite leicht bevorzugt (5a:6a 1 : 1.2). Ersetzt man die Schutzgruppe an C5 und C6 durch PhCH,O-Gruppen (4 b), so entsteht das ,,erwartete" Produkt 5b im UberschuR (5b:6b 4:l). Ausschliei3lich von der a-Seite werden die (E)/(Z)-Isomere 8 a, b angegriffen. Die Strukturen der resultierenden Verbindungen 9a, b sowie der enthalogenierten Folgeprodukte 10 a, b konnteii NMR-spektroskopisch nicht aufgeklart werden. NOE-Experimente ergeben beim Einstrahlen in die Frequenz von H3 der Verbindung 10a sowohl eine Wechselwirkung mit H5 als auch mit H72 (Zur Bezeichnung vgl. Die zum Olefin 8b 3-epimere Verbindung 11 addiert Dichlorketen nicht. Statt dessen wandert die Doppelbindung, und es entsteht im wesentlichen das Olefin 12. Hier wird deutlich, daI3 schon eine geringe Abschirmung der a-Seite durch die 3-0-Benzylgruppe in 11 den Reaktionsablauf empfindlich stort.

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High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals

Cited by 35 publications

References 11 publications

An ab Initio Study on the Allene−Isocyanic Acid and Ketene−Vinylimine [2 + 2] Cycloaddition Reaction Paths

An ab Initio Study on the Allene−Isocyanic Acid and Ketene−Vinylimine [2 + 2] Cycloaddition Reaction Paths

Remarkable High-pressure Enhancement of Enantiopure Nitrone Cycloadditions to Glycals: General Access to (1 → 2)-Linked Pseudo Aza-C-disaccharides

Chirale Cyclobutanone durch [2 + 2]‐Cycloaddition von Dichlorketen an Kohlenhydratenolether

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