S-Glycosylation
3.5
681
O-ethylbenzyl thioimidocarbonate, or potassium disulfide, respectively ( > Scheme 43). Diglycosyl disulfides have also been prepared using tetrathiomolybdate as the sulfur transferring
reagent [149]. The former product is saponified, whereas in the latter product the disulfide
bridge is reduced to give the thioaldose. With the tetrathiomolybdate reagent this could be performed in a tandem sulfur transfer/reduction/Michael reaction to afford thioglycosides directly
in a one-pot reaction ( > Scheme 44) [150].
⊡ Scheme 44
2.3 Alkylation of Thioaldoses
Thialdoses are easily S-alkylated to give the corresponding alkyl thioglycoside using alkyl
iodides or bromides under basic conditions [1]. The pseudothiouronium salt derivative
( > Scheme 36) can be used as precursor in a one-pot procedure, since the thioaldose is
obtained in situ under these conditions [1,127]. Other leaving groups, like tosylates [151],
have been used as well as a solid phase approach with the thioaldose attached to the resin
( > Scheme 45, compare > Scheme 61) [152]. Furthermore, thioalkylation using an alcohol
and Mitsunobu conditions has been reported [153]. Arylations have been performed with aryl
halides susceptible to nucleophilic displacement, e. g., 4-nitro- and 2,4-dinitrophenyl fluoride,
in the presence of, e. g., potassium carbonate [127,154,155]. Also reactions with triazene
substituted aryl iodides have been carried out using copper mediated arylation [156]. Unsubstituted iodobenzene did not react properly under the former conditions, but the thiophenyl
glucoside can be obtained by refluxing the peracetylated thioaldose in DMF in the presence of
phenylboronic acid and Cu(OAc) 2 [157].
⊡ Scheme 45
2.3.1 Via Aryldiazonium Derivatives
Apart from direct arylation using aryl halides, aryl thioglycosides can be prepared most efficiently by treatment of the thioaldose with an aryldiazonium salt followed by thermal decomposition of the produced diazo derivative ( > Scheme 46) [158]. The procedure is usually very
3.5
681
O-ethylbenzyl thioimidocarbonate, or potassium disulfide, respectively ( > Scheme 43). Diglycosyl disulfides have also been prepared using tetrathiomolybdate as the sulfur transferring
reagent [149]. The former product is saponified, whereas in the latter product the disulfide
bridge is reduced to give the thioaldose. With the tetrathiomolybdate reagent this could be performed in a tandem sulfur transfer/reduction/Michael reaction to afford thioglycosides directly
in a one-pot reaction ( > Scheme 44) [150].
⊡ Scheme 44
2.3 Alkylation of Thioaldoses
Thialdoses are easily S-alkylated to give the corresponding alkyl thioglycoside using alkyl
iodides or bromides under basic conditions [1]. The pseudothiouronium salt derivative
( > Scheme 36) can be used as precursor in a one-pot procedure, since the thioaldose is
obtained in situ under these conditions [1,127]. Other leaving groups, like tosylates [151],
have been used as well as a solid phase approach with the thioaldose attached to the resin
( > Scheme 45, compare > Scheme 61) [152]. Furthermore, thioalkylation using an alcohol
and Mitsunobu conditions has been reported [153]. Arylations have been performed with aryl
halides susceptible to nucleophilic displacement, e. g., 4-nitro- and 2,4-dinitrophenyl fluoride,
in the presence of, e. g., potassium carbonate [127,154,155]. Also reactions with triazene
substituted aryl iodides have been carried out using copper mediated arylation [156]. Unsubstituted iodobenzene did not react properly under the former conditions, but the thiophenyl
glucoside can be obtained by refluxing the peracetylated thioaldose in DMF in the presence of
phenylboronic acid and Cu(OAc) 2 [157].
⊡ Scheme 45
2.3.1 Via Aryldiazonium Derivatives
Apart from direct arylation using aryl halides, aryl thioglycosides can be prepared most efficiently by treatment of the thioaldose with an aryldiazonium salt followed by thermal decomposition of the produced diazo derivative ( > Scheme 46) [158]. The procedure is usually very