Sulfone Displacement

Scheme 5.7 illustrates these and other applications of the hydride donors. Entries 1 and 2 are examples of reduction of alkyl halides, whereas Entry 3 shows removal of an aromatic halogen. Entries 4 to 6 are sulfonate displacements, with the last example using a copper hydride reagent. Entry 7 is an epoxide ring opening. Entries 8 and 9 illustrate the difference in ease of reduction of alkynes with and without hydroxy participation. 

Imidazole-l-sulfonate Displacements at the C-3 and C-4 Positions of Sngar Derivatives. Displacement reactions of tosylates at the C-3 position of a-D-glucopyrano-side derivatives proceed with difficulty because of a nonbonded 1,3-diaxial interaction between the aglycone and the approaching nucleophile [32], as well as complications arising from neighboring group participation [90],... 

Heating the trifluoromethanesulfonate 89 in the presence of 2,6-di-tert-butyl-4-methylpyridine gave methyl 3,5-anhydro-2,6-dideoxy-/J-D-xylo-hexofuranoside 91. This rearrangement involves oxane-ring contraction 90 followed by internal sulfonate displacement.353... 

Another approach to the tricothecene skeleton proposed by Fraser-Reid takes advantage of carbohydrate enolate chemistry to constmct the A ring [366]. The C ring was formed by intramolecular sulfonate displacement by an appropriate amide enolate. A route to the same skeleton involving [2 + 2] cycloaddition on the double bond of an enone obtained from a glycal has been proposed by Fetizon [367]. Ring expansion of the cyclobutene obtained this way can be effected to constmct the C ring of these compounds. 

Sulfonate displacement has been well established as a common method for introducing halogen atoms into carbohydrates. The high reactivity and easy preparation of sulfonic esters contribute to their use in carbohydrate chemistry. Triflate displacements are popular for the preparation of secondary halogenated carbohydrates and often give satisfactory results when mesylates and tosylates fail to give products. 

Matsushima and Kino [544] have obtained the enantiomer of 429 applying AD-mix-)3-cat-alyzed dihydroxyiation of 427. Selective monosilylaltion with (f-Bu)Me2SiCl affords 438 (93% ee). After esterification of the allylic alcohol 438 with para-nitrobenzenesulfonyl chloride and subsequent sulfonate displacement with NaN3 (Sn2) azide 439 is isolated in... 

Allyl sulfides and sulfones. Displacement of bisulfite anion from RSSOjNa and... 

Figure 6.57 (b) A successful sulfonate displacement, (c) Dipole hindrance of tosylate displacements, (d) Sucralose. 

The 2 -0-p-tolylsulfonyl derivative of 8-hydroxyadenosine underwent intramolecular sulfonate displacement when heated at 100-105° with sodium benzoate in N V-dimethylformamide, and the 2, 8-anhydro structure (170) was indicated.434 A derivative of2, 8-anhydro-guanosine (171) was obtained by a similar method.435... 

D-Arabinonohydroxamic acid 5-phosphate 58, a potent transition state inhibitor of D-glucose 6-phosphate isomerase, was made from 2,3,4-tri-O-benzyl-D-arabinonic acid 5-(dibenzyl phosphate) by condensation with 0-benzylhydroxyla-mine (using carbonyldiimidazole) followed by hydrogenolysis. o-Arabinono-hydroxamic acid itself and o-threonohydroxamic acid, potent inhibitors of D-xylose isomerase, were obtained similarly. As exemplified in Scheme 11, the addition of AT-benzylhydroxylamine to unsaturated lactones such as 59 provided easy access to precursors of 3-amino-2,3-dideoxy-sugars (e.g. 60). These could be inverted at C-5 by Mitsunobu or sulfonate displacement reactions, or converted to isomeric isoxazolidines, e.g. 62, via epoxide 61. ... 

Scheme 12.1. Sulfone displacement via base-promoted 8-elimination.

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