Glucal triacetate

Unsaturated sugars are useful synthetic intermediates (11). The most commonly used are the so-called glycals (1,5- or 1,4-anhydroalditol-l-enes). In the presence of a Lewis-acid catalyst, 3,4,6-tri-0-acetyl-l,5-anhydro-2-deoxy-D-arabinohex-l-enitol [2873-29-2] commonly called D-glucal triacetate, adds nucleophiles in both kineticaHy controlled and thermodynamically controlled (soft bases predominately at C-3 and hard bases primarily at C-1) reactions (11,13). 

Previously, the reaction of 3,4,6-tri-0-acetyl-l,5-anhydro-2-deoxy-D-arabino-hex-l-enitol (D-glucal triacetate) (20) with lead thiocyanate in a mixture of acetic acid, acetic anhydride, and carbon tetrachloride had been reported by Igarashi and Honma.37 They observed formation of isothiocyanate 21 as the main product, accompanied by a mixture of four isomeric thiocyanates. 

On the other hand, methanolysis of 277 in the presence of silver carbonate and silver perchlorate gave the corresponding glycoside 278 in 83% yield, as well as the 2-thiocyanato-D-glucal triacetate 276 in 11% yield. Desulfurization of 278 with Raney nickel afforded 3,4,6-tri-O-acetyl-2-deoxy-0-D-arabino-hexopyranoside (279) in 56% yield.37... 

Several reactions were carried out with chiral olefines. For example, only one stereoisomer ii was isolated from the Patemo-Btichi reaction of D-glucal triacetate 10 with acetone (Scheme 3) [9]. 

A method using silver(I) fluoride and chlorine is sufficiently mild for the isolation of the chlorine fluoride adducts in good yield, whereas the combination of IV-chlorosuccinimide and hydrogen fluoride gives no fluorinated products. The reaction of chlorine with a suspension of D-glucal triacetate and silver(I) fluoride in an acetonitrile/benzene solution is unusual in that it gives all four possible 3,4,6-tri-0-acetyl-2-chloro-2-deoxy-D-glycopyranosyl fluorides... 

D-Glucal triacetate (1.36g, 5 nmiol) in dry MeCN (ca. 25 mL) was stirred vigorously with powdered AgF (4 g, 32 mmol). A solution of 10% Bi in benzene (w/ v, 0.85 g) was then added dropwise. After completion of the Brj addition (ca. 10 min), the solution was stirred for a further 20 min and then filtered from the copious precipitate of silver halide. To this solution was added sat. brine, the precipitated AgCI was removed, the filtrate was concentrated to ca. 10 mL and CHClj (30 niL) was added. The CHCI3 solution was extracted successively with aq NajSjOj, aq NaHCO, and H2O. After drying (Na SO j), evaporation produced a... 

The addition of the elements of IF with silver fluoride/iodine toD-glucal triacetate - leads to similar results to the corresponding bromofluorination (Section 1.2.1.3.2.). The three products are 3,4,6-tri-0-acetyl-2-deoxy-2-iodo-a-D-mannopyranosyl fluoride (5, 60 Vo), 3,4.6-tri-0-acetyl-2-deoxy-2-iodo-/l-D-glucopyranosyl fluoride (6, 34%), and 3,4,6-tri-0-acctyl-2-deoxy-2-iodo-a-D-glucopyranosyl fluoride (7,6 %). lodofluorination with hydrogen fluoride/At-iodosuccinimide gives the same three fluorides 5/6/7 in 71, 3 and 23 Vo yield. 

Takiura, K, Honda, S, Hydroxy- and acetoxy-mercuration of D-glucal triacetate, Carbohydr. Res., 23, 369-377, 1972. 

Fia. 4.—Double-resonance Tickling Experiment on n-Glucal Triacetate The Effect on H-1 of a Weak Decoupling Field Set in the Vicinity of the H-2 Resonance. 

An example of complete decoupling is shown in Fig. 5, for n-glucal triacetate it was, indeed, fortunate that the chemical shifts between H-1, H-3 and H-4, H-5 were approximately the same, so that the same experiment resulted in two simultaneous sets of decoupling. Other examples of double resonance as an aid to spectral assignments have been described by... 

Fig. 5.—Double Resonance of n-Glucal Triacetate at 100 Mc./sec. (A, decoupling H-1 from H-3, and H-4 from H-5 B, decoupling H-3 from H-1, and H-5 from H-4.)...

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