Hydroxymethyl-substituted crown acetals with 35-C-14 and 40-C-16 skeletal backbones: Synthesis and molecular geometries
S. Immel, F. W. Lichtenthaler, H. J. Lindner, and T. Nakagawa
Tetrahedron: Asymmetry2001, 12, 2767-2774.
An oxidation/reduction sequence readily
converts β- and γ-cyclodextrin into hydroxymethyl-substituted
crown acetals with 35-C-14 and 40-C-16 skeletal cores. X-Ray analysis of their well crystallizing peracetates reveals
the 40-membered ring of the γ-CD derived octaacetal to mould into an undulated four-loop
structure with alternating gauche and anti-conformations of the eight meso-butanetetrol
units, the overall shape resembling a four-leaf clover. In the β-CD derived, 35-membered
crown heptaacetal, six of the seven glycolaldehyde/butanetetrol segments are lined up
in alternating gauche/anti arrangements with the seventh, uneven unit inserted in gauche
orientation. In solution, however, the macrocycles are highly flexible as evidenced
by their 1H and 13C NMR spectra, which at 300 K show only one set of signals for the respective
-CHR-CHR-O-CHR-O- units (R = CH2OH or CH2OAc).
Immel, S.; Khanbabaee, L.,
J. Am. Chem. Soc.
Known tetraoxacycloalkanes with two acetal units in their n-crown-4 skeletal backbone: (a) 10-C-4: Bassi, I. W.; Scordamaglia, T.; Fiori, L. J. Chem. Soc., Perkin Trans. 21975, 11291132; (b) Substituted 10-C4-systems: Terzis, A.; Grindley, T. B. Can. J. Chem.1979, 57, 21542158; Stoddart, J. F.; Szarek, W. A. Can. J. Chem.1968, 46, 30613069; (c) 12-C-4; Borgen, G.; Dale, J. J. Chem. Soc., Chem. Commun.1974, 484485; Dale, J. Tetrahedron1974, 30, 16831694; (d) 14-C-4: Bassi, I. W.; Scordamaglia, R.; Fiori, L. J. Chem. Soc. Perkin Trans. 21972, 17261729; (e) 16-C-4: Dale, J.; Ekeland, T. Acta Chem. Scand., Ser. A1973, 27, 15191525; Groth, P. Acta Chem. Scand., Ser. A1975, 29, 642643; (f) 18-C-4, 24-C-4, 26-C-4, and 34-C-4: Hill, J. W.; Carothers, W. H. J. Am. Chem. Soc.1935, 57, 925928.
The cyclo-polyacetals generated by acid promoted oligomerization of 1,3-dioxolane are presumed to have 15-C-6, 20-C-8, and 25-C-10 structural backbones (Kawakami, Y.; Yamashita, Y. Macromolecules1977, 10, 837839), yet their ring size has not been established unambiguously.
French, D.; McIntyre, R.J.,
J. Am. Chem. Soc.
Stoddart, J.F.; Szarek, W.A.; Jones, J.K.N.,
Can. J. Chem.
Immel, S.; Nakagawa, T.; Lindner, H.-J.; Lichtenthaler, F.W.,
Chem. Eur. J.
Koshland, D. E. Angew. Chem.1994, 106, 24682472; Angew. Chem., Int. Ed. Engl.1994, 33, 23752378.
Ber. Dtsch. Chem. Ges.