Selective synthesis of Neu5Ac2en and its oxazoline derivative using BF3·Et2O

Facile Diastereoselective Entry to 4β‐Acylamidation of Neu5Ac2en Glycals Using Their N‐Perfluoroacylated Congeners as Key Tools

“…[22][23][24][25] Thus, we decided to bypass the formation of oxazoline 5 by strongly decreasing the nucleophilicity of the DANA acylamido group by reversible N-transacylation [15] of glycal 4 to form FANA congener 7 (Scheme 1, Path B). Indeed, oxazoline 5 is also formed to various extents during the preparation of glycal 4, upon acidic treatment of peracetylated Neu5Ac methyl ester 6, when the reaction is performed in nucleophilic solvents such as MeCN, which do not interfere in the reaction.…”

A simple synthesis of N-perfluoroacylated and N-acylated glycals of neuraminic acid with a cyclic aminic substituent at the 4α position as possible inhibitors of sialidases

“…This, at first, appeared as an inconvenience for the following glycal formation that, in all previously reported procedures, requires the activation of the 2-hydroxyl as acetate ester, as glycosyl chloride or as thioglycoside. 26,27 In fact, initial attempts to perform the direct dehydration of 2-hydroxylated compounds 9 and 10, afforded unsatisfactory results under several different conditions, even those that afforded glycal 11 as a undesired product. 28 We eventually activated the anomeric hydroxyls of compounds 9 and 10 by perfluoroacetylation with TFAA, adopting a procedure we previously set up in our work on C-glycoside synthesis promoting the elimination of anomeric hydroxyls.…”

Simple and Rapid Procedures for the Synthesis of 5‐Acylated 4β‐Acylamido‐ and 4β‐Acetoxyneuraminic Acid Glycals

“…This result is of interest because, often, the reported preparations of oxazolines, even when they occur in high yields, show the presence of the parent glycals, sometimes mixed with the glycal derived from hydrolysis of the oxazoline formed during the work‐up 18–20…”