Free-radical hydrothiolation of glycals: a thiol-ene-based synthesis of S-disaccharides

Systematic study on free radical hydrothiolation of unsaturated monosaccharide derivatives with exo- and endocyclic double bonds

“…Reaction between glycal 6 and ethanethiol showed almost complete conversion after 45 min affording a mixture of the axially and equatorially linked 2-ethylthio derivatives 7 and 8 and thioglycoside 9 in a ratio of ∼5 : 3 : 1. 30,31 Because of the poor selectivity, which was also reported by Dondoni and co-workers, 16,32 and the difficulty of separation of the diastereoisomers formed, hydrothiolation of glycal 6 was not examined further.…”

“…15 Addition of 1-thioglycoses across the endocyclic double bond of glycals showed regioselectivity but a lack of stereoselectivity, furnishing the stereoisomeric 1-deoxy S-disaccharides in about 1 : 1 ratios. 16 The incorporation of 2-acetoxy-glycals and 2,3-unsaturated glycosides within the thiol-ene coupling strategy was reported for the first time by our group. 17 We have shown that reactions between 2-acetoxy-D-glucal and a range of thiols including amino acid, peptide, and sugar thiols gave 1,2-cis-α-S-glucoconjugates and S-disaccharides with full regio-and stereoselectivities in good to excellent yields.…”

“…14 The carbohydrate skeleton itself with an exo-or endocyclic double bond has scarcely been applied as the ene partner, with only three articles published until now. [15][16][17] Dondoni and co-workers were the first to exploit the thiol-ene reaction for the synthesis of S-disaccharides by reacting sugar thiols with exo-and endoglycals. 15,16 They found that hydrothiolation of the exocyclic double bond of hex-5-enopyranoside and pent-4-enofuranoside derivatives with 1-thioglycoses afforded S-disaccharides with high yields and diastereoselectivites of up to 99%.…”

“…[15][16][17] Dondoni and co-workers were the first to exploit the thiol-ene reaction for the synthesis of S-disaccharides by reacting sugar thiols with exo-and endoglycals. 15,16 They found that hydrothiolation of the exocyclic double bond of hex-5-enopyranoside and pent-4-enofuranoside derivatives with 1-thioglycoses afforded S-disaccharides with high yields and diastereoselectivites of up to 99%. 15 Addition of 1-thioglycoses across the endocyclic double bond of glycals showed regioselectivity but a lack of stereoselectivity, furnishing the stereoisomeric 1-deoxy S-disaccharides in about 1 : 1 ratios.…”

Stereoselective Thioconjugation by Photoinduced Thiol‐ene Coupling Reactions of Hexo‐ and Pentopyranosyl d‐ and l‐Glycals at Low‐Temperature—Reactivity and Stereoselectivity Study

“…55 [ α ] D 20 =−68.4 ( c= 0.13 in CHCl 3 ) lit . −72.0; 56 [ α ] D 20 =−6.89 ( c= 0.12 in CHCl 3 ) lit . −18.8.…”