Tosyloxy groups

Replacement of one tosyloxy group m 2-fluoro-2-nitro-l,3-propanediol ditosylate by azide ion occurs easily [S5] (equation 75)... 

Compound 68 can also be obtained by an acid-catalyzed cyclization of 42, which was prepared by the Michael addition reaction of 39 to mesityl oxide as shown in Section IV.A. As for the product 69, the presence of the tosyloxy group at the 5 position instead of the 6 position is determined, utilizing the anisotropy effect of the 1-acetyl group to the C-7 proton, by comparing its H NMR spectrum with that of 70, obtained in 69% yield by the treatment of 69 with NaH and AcCl. 

S -Alkyl thiocarbamates (Table 4.24) have been synthesized [I] by a procedure (Scheme 4.19) which is closely analogous to that employed for the preparation of S-alkyl thiocarbonates (see Section 4.1), S-Glycosyl dithiocarbamates [2], which are useful precursors for thiosugars, have been prepared by simple nucleophilic displacement of the tosyloxy group by the N,N-diethyldithiocarbamate anion (cf preparation of S-glycosyl dithiocarbonates, 4.1.13). 

Oxidation of arylhydrazones 143 with HTIB in the presence of diisopro-pylethylamine produces pyrazoles 145 in one pot. The intermediate a-tosyloxy compounds 144, which are generated in situ by the oxidation of 143, undergo intramolecular participation of amino group in displacement of the tosyloxy group, thereby yielding cyclized products 145 (91SC1583). 

If the 2-0-tosylated L-rhamnono-1,4-lactone (88) was boiled in water-dioxane the 2,5-anhydride (89) was obtained in good yield. The reaction time was 16 h in this case, compared to 2-4 h in the examples in which a primary tosyloxy group was substituted. The 2,5-anhydro-carboxylic acid 89 was isolated as the methyl ester, and was shown to have the L-gZuco-configuration [117]. Thus, a clean inversion at C-2 had taken place. 

In a synthesis of nucleoside analogs, the sodium salts of phthalazine-l,4-dione, phthalazin-l(2//)-one, and two pyridazin-3(2//)-ones, prepared with sodium hydride in DMF, were alkylated with ( )-2,3-0-isopropylidene-l-0-(4-toluenesulfonyl)glycerol by a nucleophilic substitution of the tosyloxy group <1999AP327>. 

Various nucleophilic attacks at C(3) and C(4) of -lactams have been employed to introduce desired functionalities. Nucleophilic displacement of a halogen at C(3) by nucleophiles, for example, potassium phthalimide, has been performed (93JCS(Pl)2357). The a-azidation of l-hydroxy-2-azetidi-nones, for example (37), with arenesulfonyl azides in the presence of triethylamine affords 3-azido-2-azetidinones (38) via Otosylation and SN2 -type of displacement of the tosyloxy group (92JA2741, 93JA548, 93BMC2429). 

At 1650, both tosyloxy groups in 108 were replaced with inversion, and the bis(dimethylamino)-D-glucitol derivative was obtained. On heating isosorbide (3) or its diacetate (111) in the presence of such dehydrating agents as aluminum oxide in a Pyrex-glass tube above 400°, the doubly unsaturated compound 112 is formed in —50% yield194 (see Scheme 23). 

The iodo derivative is a useful intermediate for the preparation of a wide variety of different types of compounds. Primary mesyl esters also react with sodium iodide in acetone, but the selectivity of this cleavage is less because of the greater reactivity of secondary mesyl esters. oa( ) Methyl 2,3,4-tri-0-acetyl-6-0-mesyl-a-D-glucopyranoside is converted into methyl 2,3,4,6-tetra-O-acetyl-a-D-glucopyranoside with acetic anhydride and potassium acetate. Replacements of a primary mesyloxy group with fluorine by use of potassium fluoride in methanol,106 with chlorine by use of lithium chloride,102 and with pyridine to form a pyri-dinium deoxy derivative,106 have been reported. Primary tosyloxy groups have been replaced by hydrogen,106 by thiocyanate,107 and by... 

Benzoylation of free hydroxyl groups by means of benzoyl chloride in pyridine may usually be satisfactorily achieved at room temperature but, if the reaction at this temperature is prolonged or if elevated temperatures are employed, impure products (possibly containing contaminants formed by reaction, particularly of primary tosyloxy groups, with... 

An acetal ring reduces the reactivity of the 6-sulfonyloxy group, and two acetal rings may reduce it even more compare, compounds 20 and 21 26 23 and 24 32 and 43. The effect of an acetal ring (on reactivity) is greater with a mesyloxy group than with a tosyloxy group (c/., compounds 20 and 21). 

In contrast, the 6-tosyloxy group of l,6-di-0-tosylketohexofuranose derivatives is more readily replaced by iodine. Thus, by reaction during 24 hours at 90-100°, 2,3-0-isopropylidene-l,6-di-0-tosyl-L-sorbose gives264 the corresponding 6-deoxy-6-iodo-l-0-tosyl derivative (possibly accompanied by some unisolated l,6-dideoxy-l,6-diiodo derivative) and 2,3-0-isopropylidene-l,6-di-0-tosyl-D-fructose behaves266 similarly (16 hours at 100°). 

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