C O M M U N I C A T I O N S
Table 1. Synthesis of Glycosides from Propargyl Glycosidesa
gold complex (F). Acid-mediated protodemetalation of the meth-
yleneoxirane-AuCl3 complex (F) generates AuCl3 and extrudes
methyleneoxirane (G), which can further rearrange to cyclopro-
panone (H).10 Intermediate D can in turn be trapped by aglycones
to yield observed glycosides (E).
In conclusion, propargyl glycosides were identified as novel and
stable glycosyl donors. Various aglycones were reacted with
propargyl glycosides, resulting in the formation of an R,â-mixture
of glycosides and disaccharides in good yields.
Acknowledgment. S.H. thanks DST, New Delhi (SR/S1/OC-
06/2004), and DAE-BRNS Young Scientist Research Award for
financial support. S.H. is grateful for the encouragement of Dr. K.
N. Ganesh. S.K. acknowledges a CSIR Fellowship.
Supporting Information Available: Experimental procedures and
characterization data for all glycosides. This material is available free
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a All reaction were performed with 3 mol % of AuCl3, 1.0 equiv of
glycosyl donor, 1.2 equiv of aglycone in acetonitrile at 60 °C. b Isolated
and unoptimized yield. c The R:â ratio was obtained from 1H and 13C NMR
analysis. d Purified by debenzylation (Pd(OH)2/C, H2, MeOH, 12 h) of the
product followed by acetylation (Ac2O, pyridine, 4 h).
(7) General procedure for AuCl3-mediated transglycosylation: 3 mol % of
AuCl3 in acetonitrile was added to a solution of 4a (1.0 equiv) and
aglycone 6a (1.2 equiv) and heated to 60 °C for 6 h, concentrated in
vacuo, and purified by column chromatography.8 Preparation of 4a: A
solution of propargyl alcohol (15 mL, 0.25 mol) and D-glucose (10 g,
0.06 mol) in dry dioxane-HCl (135 mL) was stirred at 70 °C for 18 h,
neutralized with excess Et3N, concentrated in vacuo, and then per-O-
benzylated using NaH/BnBr/DMF.8
(8) See Supporting Information.
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2994.
Figure 2. Tentative mechanism for glycoside formation.
gold carbene intermediate (B).6i As a result of increased electro-
philicity, an intermediate of type C would be possible, which can
lead to an oxocarbenium ion (D) with the expulsion of an alkenyl
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