Indium(III) Triflate: A Highly Efficient Catalyst for Reactions of Sugars^[1]

Abstract

Indium(III) trifluoromethanesulfonate has been found to be extremely efficient in catalyzing acyl transfer reactions of various carbohydrates and their derivatives. Selective acetolyses of certain benzyl ethers/isopropylidene acetals of sugars have been possible using In(OTf)₃ in Ac₂O (neat). Reaction of the per-O-acetate of 2-deoxy-2-phthalimido-D-glucose with benzyl mercaptan in the presence of In(OTf)₃ led to the formation of the corresponding thioglycoside in high yield. Facile formation and hydrolysis of the isopropylidene and benzylidene acetals of various carbohydrates have also been achieved very efficiently in the presence of In(OTf)₃. The results show great promise for In(OTf)₃ in synthetic carbohydrate chemistry.

Keywords:

• Indium(III) triflate
• acyl transfer reactions
• acetal formation and hydrolysis
• thioglycosylation

ACKNOWLEDGMENTS

We would like to thank the Department of Science & Technology, New Delhi, India, for financial support.

Notes

^a Acetylations were carried out using 5 mL Ac₂O/g sugar at rt or as specified; for propionylation 1.05 mol equiv. of propionic anhydride per OH group of the sugar was used at rt.

^aAcetolyses were carried out using 1 mL Ac₂O/100 mg sugar derivative at rt or as specified.

^a0.032 mol equiv of In(OTf)₃ in 50 mL of acetone (HPLC grade) at reflux temperature was used.

^b 6.4 × 10^–3 molequiv of In(OTf)₃ in 200 mL of acetone (HPLC grade) at reflux temperature was used.

^c 0.25 molequiv of In(OTf)₃ in PhCHO (neat, 5 molequiv) at rt was used.

^d 15 molequiv of PhCH(OMe)₂ (neat) and In(OTf)₃ (4 mg/100 mg sugar) were used at rt.

^e 15 molequiv of Me ₂ C(OMe)₂ (neat) and In(OTf)₃ (4 mg/100 mg) were used at rt.

^a Reactions were carried out inaqueous dioxane [10%, (v/v) 1 mL/100 mg sugar] containing In(OTf)₃ [10% (w/w) sugar].