ChemInform Abstract: HIGH‐PRESSURE (2+2)CYCLOADDITION OF TOLUENE‐4‐SULFONYL ISOCYANATE TO GLYCALS

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

doi:10.1002/chin.198541219

Chemischer Informationsdienst

1985

DOI: 10.1002/chin.198541219

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ChemInform Abstract: HIGH‐PRESSURE (2+2)CYCLOADDITION OF TOLUENE‐4‐SULFONYL ISOCYANATE TO GLYCALS

Marek Chmielewski¹,

Zbigniew Kałuża²,

C. Bełżecki³

et al.

Abstract: Die Titelreaktion führt bei Anwesenheit eines Substituenten in 4‐Position des Pyranringes [vgl.

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1998

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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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mentioning

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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ChemInform Abstract: HIGH‐PRESSURE (2+2)CYCLOADDITION OF TOLUENE‐4‐SULFONYL ISOCYANATE TO GLYCALS

Abstract: Die Titelreaktion führt bei Anwesenheit eines Substituenten in 4‐Position des Pyranringes [vgl.

Cited by 1 publication

References 1 publication

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

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

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