Phenylmercury methoxide

Several methods were described for the selective de-S-acetylation of 0-acetyl protected 1-thioglycoses. Sodium methoxide in methanol at low temperature (below -20 °C) was known to afford mainly the de-S-acetylated compound [16] or exclusively this compound when the reaction was quenched at low temperature by adding H-l- resin [17]. Demercuration of tetra-O-acetyl-l-phenylmercury(II)-thio- -D-glucopyranose (12) (Scheme 4) obtained by treatment of (8e) with phenylmercury(II)acetate afforded a convenient synthesis of tetra-0-acetyl-l-thio-/3-D-glucose (8a) [18]. This sequence applied to the a-anomer (10a) (Scheme 3) led to the expected de-S-acetylated compound (10b) [19]. Chemoselective deprotection of thioacetate at the anomeric position of peracetylated 1-thioglycoses was also achieved in good yield by action of cysteamine in acetonitrile or hydrazinium acetate in DMF [20,11]. 

Chemoselective cleavage of anomeric thioacetates to the thioaldose in the presence of O-acetyl groups is possible under various conditions, e. g., methanolic sodium methoxide at low temperatures [121], phenylmercury acetate followed by demercuration [122], 2-aminoethanethi-ol [123], or hydrazinium acetate [124], and these methods have therefore often been used in the synthesis of thiooligosaccharides (O Sect. 3.2.1). As mentioned, glycosyl thioacetates can also be prepared from the 2-acetoxyglycal derivative (see Scheme 24). 

There are several methods for the selective S-deacetylation of thioglycoses one of the most successful of these is demercuration of phenylmercury thio-a- or -P-D-glycoses [22, 23]. Deprotection has also been achieved by use of sodium methoxide... 

---

See also in sourсe #XX -- [ ]

---