Indium Trichloride Mediated Cleavage of Acetonides in the Presence of Acid-Labile Functional Groups - Enhancing the Synthetic Utility of 1,3-Dioxolanyl-Substituted 1,2-Oxazines

Fabian Pfrengle, Vjekoslav Dekaris, Luise Schefzig, Reinhold Zimmer, Hans-Ulrich Reissig*

*Institut für Chemie und Biochemie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin, Germany, Email: hans.reissigchemie.fu-berlin.de

F. Pfrengle, V. Dekaris, L. Schefzig, R. Zimmer, H.-U. Reissig, Synlett, 2008, 2965-2968.

DOI: 10.1055/s-0028-1083628

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Abstract

Indium trichloride in an acetonitrile-water mixture chemoselectively cleaved the isopropylidene acetals of various 1,3-dioxolanyl-substituted 1,2-oxazines as well as carbohydrate derivatives. Enol ethers, glycosidic linkages and acid-sensitive protecting groups such as tert-butyldimethylsilyl, 2-(trimethylsilyl)ethyl, or tert-butoxycarbonyl are not attacked.

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The selective cleavage of the isopropylidene acetals is a difficult task for the shown structures, because use of Lewis acids such as SnCl₄, TMSOTf, BF₃OEt, Bu₂BOTf, or Et₂AlCl leads to the formation of bicyclic 1,2-oxazinones, whereas Brønstedt acids such as HF-pyridine, HCl in MeOH, or DOWEX-H⁺ give bicyclic tetrahydrofurans.

Reactions using Lewis or Brønstedt acids instead of InCl₃

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Key Words

deprotection, 1,2-oxazines, isopropylidene acetals, Lewis acids, indium trichloride

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ID: J60-Y2008-3570