The selective sulfonylation of 1 ,Sanhydroalditolsr -3 having the gluco and xylo configurations has previously been investigated, and the effects of the aglycon on the relative reactivity of the hydroxyl groups have been reported. The selective tosylation of 1,5-anhydro-D-galactitol (1) is now described.
Reaction of 1 with three molar equivalents of p-toluenesulfonyl chloride in pyridine at 0" gave a mixture that was fractionated on silica gel to afford the 2,3,4,6tetrasulfonate 2 (6 %), the 2,3,6-trisulfonate 3 (76 %), the 3,Gdisulfonate 4 (15 %), and the 6-sulfonate 5 (2%).
Dimolar tosylation of 1 gave a product mixture from which 3 (12 %), 4 (47 %), and 5 (6 %,I were isolated, after column chromatography.
The structure of 3 was established by comparison of the p.m.r. spectra of 3 and its benzoate 6. The signal of H-4 in the spectrum of 3 appeared at higher field than those of H-2 and H-3, whereas a doublet characteristic of the H-4 signal of 6 occurred to low field of ail other ring-proton resonances. This finding indicates that C-4 of 3 and 6 is substituted with a hydroxyl and a benzoyl group, respectively.
The structure of 4 was confirmed by preparing the dibenzoate, which was shown to be I,5-anhydro-2,4-di-O-benzoyl-3,6-di-O-~-tolylsulfonyl-~-galactitol (7) by p.m.r. spectroscopy. The signals of H-2 and H-4 of 7 appeared to the lowest field of the ringproton resonances, because of the deshielding effect of benzoyloxy groups on the same methine protons at C-2 and C-4.
The structure of 5 was demonstrated by benzoylation of 5 to give the known 1 ,5-anhydro-2,3,4-tri-O-benzoyl-6-O-~-tolylsulfonyl-~-galactitol4 (8). The respective isolation of 3 and 4 as the major product from trimolar and dimolar tosylation of 1 shows that the order of the relative reactivity of the hydroxyl groups of 1 is OH-4 > OH-3 > OH-2 > OH-4. The finding that the OH-3 group is the most reactive among the ring-hydroxyl groups is in agreement with the result? of selective sulfonylation of galactopyranosides, as explained by an effect of the C~S OH-3-OH-4 hydrogen-bonding. The lowest reactivity of the OH-4 group in 1 is consistent with the results' of selective benzoylation and sulfonylation of galacto-