Cycloaddition Reactions of 1,3-Diaza-2-azoniaallene Salts and Glycals

✍ Scribed by Min Weng; Armin Geyer; Anke Friemel; J. C. Jochims; Martin Lutz

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 100 KB
• Volume: 342
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/1521-3897(200006)342:5<486::aid-prac486>3.0.co;2-s

✦ Synopsis

Only a few reports deal with Diels-Alder or 1,3-dipolar cycloaddition reactions of glycals . For instance, azodicarboxylates undergo Diels-Alder cycloaddition with glycals to afford oxadiazines [2 -9]. The method allows the stereoselective introduction of a nitrogen atom on C-2 of a carbohydrate, and has been used to prepare complex 2-deoxy-2-amino saccharides under mild conditions in high yields. A synthesis of (-)-cryptosporin started with a two-step Diels-Alder cycloaddition of an isoquinolinium salt on L-fucal . Effective Diels-Alder cycloadditions of α-oxothiones and glycals have been reported . Cycloadditions of glycals with trichloroacetyl isocyanate afforded mixtures of βlac-tams and Diels-Alder cycloadducts [12 -14].

Little is known about 1,3-dipolar cycloaddition chemistry employing glycals. At -78 °C N-tosyl phenylaziridine in the presence of BF 3 •Et 2 O has been reported to react as 1,3-dipole with dihydropyran . Under rather drastic conditions (100 °C, long reaction times) certain cyclic nitrones have been added to glycals in moderate yields . Better yields were obtained by intramolecular cycloaddition of nitrones and also of nitrile oxides to the double bond of glycals . Most noteworthy, a manganese nitrido complex upon activation with trifluoroacetic anhydride has been reported to serve as a reactive nitrogen transfer agent to glycals affording stereoselectively high yields of 2-deoxy-2-amino saccharides . Although the mechanism of this reaction does not seem to be clear, the isolation of an oxazoline intermediate is formally in line with a 1,3dipolar cycloaddition reaction of an acyl nitrene (F 3 CC=O)N to the electron-rich glycal double bond.