Lyxopyranosyl chloride

D-Lyxose yielded a D-lyxosyl chloride 2,3,4-tri(chlorosulfate) which, on treatment with chloride ion, led to a dichlorodideoxy compound, most probably 2,4-dichloro-2,4-dideoxy-L-arabinose.353 D-Glucose gave a compound presumed to be 4,6-dichloro-4,6-dideoxy-a,/3-D-galactosyl chloride 2,3-di(chlorosulfate),360 and D-xylose afforded a monochloromonodeoxy derivative formulated, on indirect evidence, as 4-chloro-4-deoxy-L-arabinopyranosyl chloride 2,3-di(chlorosulfate).360 3,4-Dichloro-3,4-dideoxy-/3-D-ribopyranosyl chloride 2-(chlorosulfate) was the major, and 4-chloro-4-deoxy-a-D-xylopyranosyl chloride 2,3-di(chlorosulfate) the minor, product from the reaction of L-arabinose with sulfuryl chloride at room temperature for 24 hours.357,361 It has been established that, on reaction with sulfuryl chloride at low temperature, crystalline a-D-xylopyranose and /3-D-lyxopyranose afford, respectively, the 2,4,6-tri(chlorosul-fate)s of /3-D-xylopyranosyl chloride and a-D-lyxopyranosyl chloride,362 363 confirming that substitution at C-l occurs by an Sn2 process on a l-(chlorosulfuric) ester intermediate. 

An elegant, stereospecific synthesis of two 2-chloro-2-deoxy-pentoses was achieved during the course of a study of the anomerization of chlorosulfated glycosyl chlorides.40 It had been found37 that attempts to anomerize /3-D-xylopyranosyl chloride 2,3,4-tri(chloro-sulfate) (14) with 0.25 mol-equivalent of aluminum chloride afforded the crystalline a-D anomer only in low yield formed also was another compound whose structure has been established40 to be that of 2-chloro-2-deoxy-a-D-lyxopyranosyl chloride 3,4-di(chlorosulfate) (16). The dichloro derivative 16 became the exclusive product when 1.5 mol-equivalents of aluminum chloride were used treatment of 16 with sodium iodide yielded crystalline 2-chloro-2-deoxy-D-lyxose. Similarly, a-D-lyxopyranosyl chloride 2,3,4-tri(chlorosulfate) (15) afforded 2-chloro-2-deoxy-a-D-xylopyranosyl chloride 3,4-di(chlorosuI-fate) (17). 

C-l, to give initially a chloronium ion, as shown. Favored attack by chloride ion at the mors highly reactive center (C-l) would result in a net inversion of configuration at C-2 of 27, t( yield 29. In the reaction of a-D-lyxopyranosyl chloride 2,3,4-tri(chlorosulfate) 28 wit aluminum chloride, a 1,2-cis product 30 was preponderant, whereas the proposed mechanisrr should yield a 1,2-trans product this result is, presumably, due to the anomerization of the thermodynamically less-stable p anomer of 30 to the (more stable) 1,2-cij product 30. 

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