Sc(OTf)₃ as Efficient Catalyst for Aryl C-Glycoside Synthesis

Abstracts

Sc(OTf)₃ was found to be an efficient catalyst for the C-glycosylation of phenols. Reactions of various functionalized phenols and glycosyl acetates, including an azido-bearing one, are achieved by using a catalytic amount of Sc(OTf)₃ (10 mol% for neutral sugars or 50 mol% for an azido sugar) under mild conditions.

Key words

aryl C-glycosides - O→C-glycoside rearrangement - scandium triflate - catalysis - ravidomycin

References

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10

This work was presented at the 83rd Annual Meeting of the Chemical Society of Japan, March 2003, Tokyo, Abstract 2D-1-38.

11

The α-isomer was used for this study. Synthesis of 2 will be reported elsewhere.

13

Selected data of ¹H NMR, ¹³C NMR, NOE and HMBC are shown below (Figure [2] ).

14

Experimantal procedure as follows: To a stirred mixture of Sc(OTf)₃ (210 mg, 0.427 mmol; Aldrich, 99.995%), phenol 3 (417 mg, 1.28 mmol), powdered Drierite^® (2.6 g) in 1,2-dichloroethane (15 mL), was added acetate 2 (361 mg, 0.878 mmol) in 1,2-dichloroethane (8 mL) at -30 °C. After the temperature was gradually raised to 12 °C during 0.5 h, the mixture was poured into sat. aq NaHCO₃ solution. After filtration through a Celite pad, the products were extracted with EtOAc (3×), and the combined organic extracts were washed with brine, and dried over Na₂SO₄. Removal of the solvents in vacuo and purification by silica-gel column chromatography (hexane/EtOAc = 5:1) afforded C-glycoside β-4 as white powder (462 mg, 78%).

15

Typical experimental procedure for the aryl C-glycosylation of neutral sugars is described for the reaction of phenol 3 and glycosyl acetate 5a: To a stirred mixture of Sc(OTf)₃ (6.7 mg, 14 µmol), phenol 3 (87.7 mg, 0.269 mmol), powdered Drierite^® (403 mg) in 1,2-dichloroethane (1.5 mL), was added acetate 5a (49.8 mg, 0.134 mmol) in 1,2-dichloroethane (1.0 mL) at -30 °C. After the temperature was gradually raised to -10 °C during 1.0 h, the reaction was quenched with sat. aq NaHCO₃ solution. After filtration through a Celite pad, the products were extracted with EtOAc (3×), and the combined organic extracts were washed with brine, and dried over Na₂SO₄. Removal of the solvents in vacuo and purification on silica-gel preparative TLC (hexane/acetone = 2:1) afforded C-glycoside 6a as white powder (75.9 mg, 89%).