Dibenzyl dithioacetal, reaction with

Dithioacetal derivatives have also been employed56 in reactions with 23. The primary hydroxyl group in 2,3 4,5-di-0-isopropylidene-D-galactose diethyl and dibenzyl dithioacetals is readily replaced by iodine, to give the expected 6-deoxy-6-iodo derivatives in almost quantitative yields. The secondary hydroxyl group in 5-0-benzoyl-2,3-0-isopropylidene-L-arabinose diethyl dithioacetal (32) was similarly replaced by iodine to give 5-0-benzoyl-4-deoxy-4-iodo-2,3-O-isopropylidene-D-xylose diethyl dithioacetal (33) however, a rearranged product, namely, 4-0-benzoyl-5-deoxy-5-iodo-2,3-0-iso-propylidene-L-arabinose diethyl dithioacetal (34) was also produced. 

Benzyl 1,5-dithio-L-idopyranosidc (342) was obtained by intramolecular cyclization of the dibenzyl dithioacetal of D-glucose having a sulfonyloxy group at C-5 (Scheme 86) This reaction was first observed with 5-0-tosyl-L-arabinose dibenzyl dithioacetal by Harness and Hughes in 1971, and later reexamined It was shown that protection of the hydroxyl groups, prior to the cyclization with sodium iodide and barium carbonate, increased the yield considerably... 

The fused 1,2,3-triazolino-pyrrolidine 84 was obtained by oxidation of 2,3,4-tri-0-acetyl-5-azido-5-deoxy-D-xylose dibenzyl dithioacetal with MCPBA, the reaction involving intramolecular dipolar cycloaddition of the azido group onto a 1,2-double bond formed by loss of acetic acid. A similar product was obtained from the D-rt o-analogue. Nucleotide analogues based on hexenopyranosyl phosphonic acid derivatives with a nucleoside base moiety linked at C-4 are covered in Chapters 9 (Section 2.6) and 17. 

D-Xylose has been converted to (25)-3-(indol-3-yl)propane-l,2-diol 237 by two different routes, one involving direct Fischer indolization of 238. The dibenzyl-dithioacetal 239 was elaborated to the fused triazoline 240 following reaction with MCPBA. Initial oxidation was followed by elimination of acetic acid allowing intramolecular 1,3-dipolar cycloaddition reaction to construct the triazole ring. The bicyclic iV,S -acetals 242 and 241 were prepared by reaction of the 2,3-0-isopropylidene-D-ribofuranose with 2-aminoethane thiol followed by Mitsunobu reaction. These products are considered analogues of castanosper-mine and australine. ... 

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