The use of silyl groups in the synthesis of arabinofuranosides

Five Triisopropylsilyl Substituents in Ara‐β‐(1→2)‐Ara Disaccharide Glycosyl Donor Make Unselective Glycosylation Reaction Stereoselective

“…This result correlates with known theory [18] that a bridging group [6b] at positions O‐3 and O‐5 locks the E 3 conformation of the glycosyl cation, thus favoring 1,2‐ cis ‐glycosylation. Taking into account that TFA groups have the same deactivating effect [6o] as the DTBS group, locking the conformation of the glycosyl cation and, as a consequence, stereoselective 1,2‐ cis‐ glycosylation can be also achieved with the use of a single bulky acyclic TIPS group at O‐2 in glycosyl donor. In case of the use of Ara‐β‐(1→2)‐Ara disaccharide glycosyl donor, which contains only O ‐benzoyl substituents, we observed the absence of stereocontrol (α : β=1 : 2–1 : 2.5).…”

“…It is important to note that the synthesis of 1,2‐ cis ‐β‐arabinofuranosides is more demanding than the preparation of 1,2‐ trans ‐α‐arabinofuranosides, which can be easily accessed using glycosyl donors with participating acyl groups at O‐2 [6c,f,h,k–o,7] . 2‐ O ‐Benzyl‐containing glycosyl donors are mainly used for the installation of 1,2‐ cis ‐glycosidic linkages in oligoarabinofuranosides.…”

“…However, hydrogenolytic cleavage of O ‐benzyl protective groups in oligosaccharides containing an azido group in aglycone is not straightforward [6c] . We have recently showcased the benefits of the benzyl‐free approach for the synthesis of the terminal di‐, penta‐ and hexasaccharide fragments of M. tuberculosis arabinans with azido group in aglycone using glycosyl donors with O‐2 protected by triisopropylsilyl (TIPS) nonparticipating group [6o,8] …”

Iron-catalyzed aerobic oxidation of silyl ethers to carboxylic acids

“…The hydroxy group is a versatile reactive functional group, and silyl groups are commonly used for protecting this functionality aimed at targeted transformations, which would be followed by deprotective oxidation in organic synthesis (Scheme 1A). 1,2 Catalytic aerobic oxidation has been developed for the deprotective oxidation of silyl ethers to afford aldehydes and ketones. 3 The pioneering preparation of carboxylic acids directly from silyl ethers generally lacks efficiency or suffers from functional group tolerance (Scheme 1B).…”