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

The structures of three racemic (tetra-hydro-[1,3]dioxino[5,4- d ][1,3]dioxin-4-yl)methanol derivatives are reported, namely, 4-[(methyl-sulfon-yloxy)meth-yl]-2,4,4a,6,8,8a-hexa-hydro-[1,3]dioxino[5,4- d ][1,3]dioxine, C 8 H 14 O 7 S, 1 , 4-[(benz-yloxy)meth-yl]-2,4,4a,6,8,8a-hexa-hydro-[1,3]dioxino[5,4- d ][1,3]dioxine, C 14 H 18 O 5 , 2 , and 4-[(anilinocarbon-yl)meth-yl]-2,4,4a,6,8,8a-hexa-hydro-[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 inter-est because of the conformation of the cis -fused tetra-oxadeca-lin ring system. This cis -bi-cyclo-[4.4.0]decane ring system, i.e. cis -deca-lin, 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 dihy-droxy aldehyde and tosyl-ate analogs.