Structures of rac-2,4:3,5-di-methyl-ene xylitol -derivatives

The crystal structures of three xylitol derivatives prepared directly from commercially available xylitol by treatment with formalin and acid followed by subsequent derivatization of the primary hydroxyl group of the bis-methyl­ene ketal with mesyl chloride, benzyl bromide or phenyl iso­cyanate are reported. The structures of three racemic (tetra­hydro-[1,3]dioxino[5,4- d ][1,3]dioxin-4-yl)methanol derivatives are reported, namely, 4-[(methyl­sulfon­yloxy)meth­yl]-2,4,4a,6,8,8a-hexa­hydro-[1,3]dioxino[5,4- d ][1,3]dioxine, C 8 H 14 O 7 S, 1 , 4-[(benz­yloxy)meth­yl]-2,4,4a,6,8,8a-hexa­hydro-[1,3]dioxino[5,4- d ][1,3]dioxine, C 14 H 18 O 5 , 2 , and 4-[(anilinocarbon­yl)meth­yl]-2,4,4a,6,8,8a-hexa­hydro-[1,3]dioxino[5,4- d ][1,3]dioxine, C 14 H 17 NO 6 , 3 . Mesylate ester 1 at 173 K has triclinic P symmetry and both benzyl ether 2 at 173 K and phenyl urethane 3 have monoclinic P 2 1 / c symmetry. These structures are of inter­est because of the conformation of the cis -fused tetra­oxadeca­lin ring system. This cis -bi­cyclo­[4.4.0]decane ring system, i.e. cis -deca­lin, can undergo conformational equilibration. In the two most stable conformers, both six-membered rings adopt a chair conformation. However, there are significant consequences in these two stable conformers, with heteroatom substitution at the 1,3,5,7-ring positions as described. Only one conformation, denoted as ‘concave’ or ‘inside’, is found in these crystal structures. This is consistent with previously reported structures of the 1,1-geminal dihy­droxy aldehyde and tosyl­ate analogs.