Synthesis of rigid <i>p</i>-terphenyl-linked carbohydrate mimetics
作者:Maja Kandziora、Hans-Ulrich Reissig
DOI:10.3762/bjoc.10.182
日期:——
2-oxazine, was prepared by a stereoselective [3 + 3]-cyclization of a D-isoascorbic acid-derived (Z)-nitrone and lithiated TMSE-allene. The Lewis acid-induced rearrangement of this heterocycle provided the corresponding bicyclic 1,2-oxazine derivative that may be regarded as internally protected amino sugar analogue. After subsequent reduction of the carbonyl group, the resulting bicyclic compound was used
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
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. Deprotection of acetonides can be achieved in substrates susceptible for acid-induced cyclizations. Most importantly, enol ether moieties are not attacked and the presence of glycosidic linkages or acid-sensitive protecting groups such as tert-butyldimethylsilyl, 2-(trimethylsilyl)ethyl, or tert-butoxycarbonyl is also tolerated.
concealed: 1,2‐oxazines such as 1 rearrange under Lewisacidic conditions to bicyclic products of type 2, which can be incorporated into oligosaccharides as protected aminosugar equivalents. Subsequent reductive steps provide unusual oligosaccharides 3 having C2‐branched 4‐aminosugar units. Most of the reactions proceed with excellent stereocontrol and allow the synthesis of a collection of stereoisomers