2.3- 0-isopropylidene-6-thio

Reduction of 6-S-benzyl-2,3-0-isopropylidene-6-thio-l-0-p-tolyl-sulfonyl-/3-D-fructofuranose with lithium aluminum hydride in tetrahydrofuran caused desulfonyloxylation to 6-S-benzyl-l-deoxy-... 

Fructofuranose, 6-S-benzyl-l-deoxy-2,3-0-isopropylidene-6-thio-/3-D-, 274 Fructopyranose, 6-acetamido-6-deoxy-D-, 178... 

Anhydro-a-D-fructofuranose 3,6-anhydro-P-D-fructofuranose 1,2 2,l -dianhydride (64) 6-Azido-6-deoxy-a-D-fructofuranose 6-deoxy-P-D-t/ reo-hex-5-enofuranose 1,2 2,1 -dianhydride" (65) 6-5-Heptyl-6-thio-a-D-fructofuranose 6-deoxy-p-D-tft eo-hex-5-enofuranose 1,2 2,l -dianhydride" (66) 4,5 4, 5 -Di-0-isopropylidene-di-p-D-fructopyranose 1,2 2,l -dianhydride (67) 6,6 -Dideoxy-6,6 -diiodo-di-p-D-fructofuranose 1,2 2,1 -dianhydride (68)... 

C13H2405S Ethyl 2,3 4,5-di-0-isopropylidene-l-thio-yS-D-glucoseptano-side 30 465... 

Mootoo and co-workers disclosed a procedure for the preparation of C-l substituted galactals based on the intramolecular capture of an oxocarbenium ion by an enol ether residue.79 In their approach, the key intermediate 1 -thio-1,2-O-isopropylidene acetals (TIA) are activated with methyl triflate to generate the crucial annulating synthon (1,2-O-isopropylidenated oxocarbenium ion). 

Similar addition of other lithiated thio derivatives to substituted aldonolac-tones has been performed (69). Thus, reaction of tris(methylthio)methyl-lithium to benzylidenated or isopropylidenated aldonolactones, followed by mercury(II)-catalyzed desulfuration, led to derivatives of glyc-2-ulosonic acids. 

The thermal ring closure of isopropylidene N-[amino(thio)carbonyl]ami-nomethylenemalonates (439, X = O, S) in boiling diphenyl ether for 5 min afforded uracil and thiouracil (1193, X = O, S) in 68% and 70% yields, respectively (84SC96I). 

Scheme 13.—Photochemical Cleavage of 6-0-(Dimethylthiocarbamoyl)-l,2 3,4-di-0-isopropylidene-a-D-galactopyranose (9) and of l,2 3,4-Di-0-isopropylidene-6-0-[(methyl-thio)thiocarbonyl]-a-D-galactopyranose (12).

Scheme 26 Synthesis of 4-thio-L-lyxono-1,4-lactone from 2,3-0-isopropylidene-5-0-tosyl-D-ribonolactone...

The value of some nucleosides for use as flavor enhancers,1348 and the possible antiviral or antitumor activity of certain nucleosides,135 have led to the synthesis of purine nucleosides containing analogs of D-apiose in which the ring-oxygen atom of the furanose forms has been replaced.136 Monomolar p-toluenesulfonylation of 3-C-(hydroxy-methyl)-l,2-0-isopropylidene-/3-L-threofuranose (50) yielded 3-C-(hydroxymethyl)-l,2-0-isopropylidene-31-0-p-tolylsulfonyl-/3-L-thre-ofuranose (51) which, through a series of steps, was converted into either methyl 2,3-O-isopropylidene- [3-C-(hydroxymethyl)-4-thio-/3-D-... 

For the preparation of a 3 -deoxy Lex analogue, an acylated 3-deoxy-D-. v/o-hexopyranose was used. The latter was prepared either from phenyl 1-thio-D-galactopyranoside78 or from l,2 5,6-di-0-isopropylidene-a-D-galactofuranose,79 via the Barton and McCombie deoxygenation method. 

A. Fleetwood and V. Hughes, Convenient synthesis of 2,3-0-isopropylidene-5-thio-D-ribose and 5-thio-D-ribose synthesis of l,4-anhydro-2,3-0-isopropylidene-u-D-ribo-pyranose and l,4-anhydro-2,3-0-isopropylidene-5-thio-u-D-ribopyranose, Carhohydr. Res., 317 (1999) 204-209. 

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