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 (free Supporting Information)
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.
see article for more examples
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
deprotection, 1,2-oxazines, isopropylidene acetals, Lewis acids, indium trichloride