Pent-4-enofuranose preparation

Of the four possible 5-deoxy-pent-4-enofuranoses, the D-erythro-isomer was of interest as a potential source of derivatives of L-lyxofuranose. For this purpose, a vinyl ether having the D-en/ hro-configuration has been prepared from derivatives of D-ribose. Condensation of D-ribose with acetone in the presence of methanol, cupric sulfate and sulfuric acid at 30°C., as described by Levene and Stiller(30) afforded a sirupy product consisting mainly of methyl 2,3-O-isopropylidene-D-ribofuranose (40). Treatment of a pyridine solution of the sirup with tosyl chloride... 

F rom 5-deoxy-5-iodo-1,2-0-isopropylidene-/ -l-arabinofura-nose (37). Anhydrous silver fluoride (600 mg.) was added to a solution of 300 mg. of 37 in pyridine (4.0 ml.), and the mixture was shaken at room temperature for 24 hours. Ether (4 ml.) was added, and the mixture was passed through a column of silica gel (1.5 X 12 cm.). The column was washed with ether/pyridine, 1 1 v/v. (10 ml.), and the effluent, which contained 5-deoxy-l,2-0-isopropylidene-/ -L-threo-pent-4-enofuranose (33), was concentrated to 4 ml. Acetic anhydride (0.2 ml.) was added, and the reaction mixture was kept at room temperature for 16 hours. Concentration afforded a sirup from which the last traces of solvent were removed by storage in high vacuum at 20°C. The sirup was distilled at 90°C. (bath) at 2.5 X HHmm. The distillate (110 mg., 51%), which crystallized on standing, had physical constants which were identical to material prepared as above. 

The use of the pseudohalogen nitryl iodide, prepared in situ from iodine and silver nitrite, has been found to add to an alkene in what is strictly an anti-Markownikov fashion. The explanation for this lies in that nitryl iodide adds in a radical manner, initially forming the more stable secondary radical after addition of NO2.115 Treatment of 3-0-acetyl-5,6-dideoxy-1,2-0-isopropylidene-a-D-xy/o-hex-5-enofuranose with nitryl iodide was found to afford an unstable adduct, with the nitro group appended to C-6, and iodine attached to the more substituted C-5.116-118 Similarly, treatment of benzyl 2-0-benzyl-3,4-dideoxy-a-D-g/ycero-pent-3-enopyranoside (70, Scheme 19) with nitryl iodide afforded the unstable adduct 71, which, upon exposure to mild base (NaHC03), afforded the eliminated product, namely benzyl 2-0-benzyl-3,4-dideoxy-4-nitro-a-D-g(ycew-pent-3-enopyranoside (72). The eliminated product was then readily converted into benzyl 2-0-benzyl-3,4-dideoxy-(3-L-r/ireo-pentopyranoside (73) by reduction with sodium borohydride. Addition of deuteride using NaBD4 led to axial deuteration atC-3. 

Attempts to prepare esterified glycals by the reduction of glycofuranosly halides with zinc in acetic acid failed, because of the reactivity of this class of compound (see p. 92). When, however, 3,5-di-0-benzoyl-2-0-(p-nitrophenylsulfonyl)-/3-D-ribofuranosyl bromide (8) in acetone is treated at 5° with sodium iodide, a facile elimination takes place and 3,5-di-O-benzoyl-1,2-dideoxy-D-er2/i/iro-pent-l-enofuranose (9) is obtained crystalline, in 72% yield. The product was characterized by identifying its hydrogenation product as the known l,4-anhydro-3,5-di-0-benzoyl-2-deoxy-D-er2/nuclear magnetic resonance spectrum, which showed clearly that the glycal structure was present. 

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