A Ring Contraction of 2,3-Di- O-Silylated Thiopyranosides To Give Thiofuranosides under Mildly Acidic Conditions

Organic Letters
Polina I AbroninaLeonid O Kononov

Abstract

A pyranose ring contraction of ethyl 1-thio-β-d-galactopyranosides has been discovered that proceeds with retention of aglycon under mildly acidic conditions (aq TFA in CH2Cl2). Key factors for success of this rearrangement are the presence of bulky silyl (TIPS or TBDPS) substituents at both O-2 and O-3 and a free hydroxy group at C-4 (derivatives with acid-labile protective groups at O-4 will also engage in this reaction). The rearrangement cleanly proceeds for 2,3-di- O-TIPS derivatives with two hydroxy groups at C-4 and C-6, acid-labile TES groups at O-4 and O-6, or one acyl substituent (Bz, ClAc) at O-6. A possibility to switch the direction of the debenzylidenation reaction in 4,6- O-benzylidene-2,3-di- O-TIPS/TBDPS derivatives by the choice of an acid (TFA, which cleanly gives furanose, versus AcOH, which cleaves benzylidene acetal only) may present an advantage in the divergent synthesis of selectively protected glycosyl donors (either in furanose or pyranose form) useful for the synthesis of biologically important oligosaccharides.

References

Feb 23, 1996·Carbohydrate Research·M NagaokaT Yokokura
Jul 3, 2007·Journal of the American Chemical Society·Christian Marcus PedersenMikael Bols
Jul 11, 2009·Chembiochem : a European Journal of Chemical Biology·Michele R Richards, Todd L Lowary
Mar 23, 2011·Journal of the American Chemical Society·Hiroko SatohJürg Hutter
Feb 28, 2016·The Journal of Microbiology·Mark J Lee, Donald C Sheppard
Nov 25, 2016·Carbohydrate Research·Leonid O KononovAlexander O Chizhov
Feb 24, 2017·Beilstein Journal of Organic Chemistry·Mikael Bols, Christian Marcus Pedersen

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Citations

May 17, 2019·Organic & Biomolecular Chemistry·Julien MalassisBruno Linclau

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