Tipson-Cohen reagent

Simple elimination did not occur as in the pyranoid series (see p. 232) when 2,3-frans-sulfonic esters were treated with the Tipson-Cohen reagent (sodium iodide and zinc in N,N-dimethylformamide) instead, 2,5-anhydro-3,4-di-0-p-tolylsulfonyl-D-xylose diisobutyl dithioacetal underwent a double elimination72 but see Ref. 76a. An alternative means of preparing 2,5-dihydrofuran derivatives that has its analogy in the pyranoid series (see p. 233) is, however, the treatment of appropriate aziridines with sodium nitrite in acetic acid, and, by this means, compound 41 [R = CH(S-isoBu)2, R = H] has been prepared in high yield.77... 

Alternatively, Horton and coworkers recommend the use of 2,3-disulfonic esters of methyl 4,6-O-benzylidene-a-D-glucopyranoside for the preparation of the olefin 45. Heating such compounds with potassium ethylxanthate in boiling butanol, or with the Tipson-Cohen reagent (N,N-dimethylformamide, sodium iodide, and zinc dust) afforded the product in 40-55% yield, and methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside and the 2,3-epithio analog also gave this compound under the former conditions.81 Applied to vicinal di-... 

Amino-3-deoxy compounds related to the olefin (79, R = R = H) have been prepared by application of the Tipson-Cohen reagent.1413... 

Dehydrochlorination of 2,3,5-tri-O-benzyl-a-D-arabinofuranosyl chloride using a molecular sieve gave the benzylated 2-hydroxyglycal (223). A mixture of three substituted furans, namely 2-[(isobutylthio)methyl]furan (224) and its 3-and 4-isobutylthio-derivatives [(225) and (226), respectively] was obtained when 2,5-anhydro-3,4-di-0-toluene-p-sulphonyl-D-xylose di-isobutyl dithioacetal (227) reacted with sodium iodide-zinc in DMF (the Tipson-Cohen reagent) at 150 C. ... 

By contrast, 2,5-anhydro-3,4-di-0-toluene-p-suIphonyl-D-xyIose ethylene dithio-acetal (228), its D-ribose epimer, and the analogous L-arabinose di-isobutyl dithioacetal all reacted with the Tipson-Cohen reagent by an 2-type mechanism with formation of the anticipated 3-alkenes. 

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