TUD Organische Chemie

Immel

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Abstract 25

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Large Ring Crown Acetals From Cyclodextrins

S. Immel

Proceedings of the 10^th Internat. Symp. on Cyclodextrins (Ed.: J. Szejtli), Mia Digital Publ., Ann Arbor, Michigan, 2000, pp. 18- 23.

Kandra et al. reported the β-CD-derived title compound as its amorphous, chiral ([α]_D = -0.1) per-O-acetate (I_β),^[1] suggesting it to be impure. Similarly, we have elaborated the periodate oxidation of α-, β-, and γ-CDs, CDs, followed by borohydride reduction, to give the respective 30-, 35-;, and 40-memebered cyclic crown acetals, which were isolated and characterized in the form of their achiral crystalline per-O-acetates (I_α - I_γ). X-Ray analysis of these compounds revealed their unique topology: in I_α with approximate C₃ symmetry, three acetoxyethylidene units are located inside the macro-ring and the other three outside. Of the six acetoxy-meso-butanetetrol units, three are in a gauche and the other three in a trans arrangement, alternatively (Fig. 1). The macrocyclic frames of I_β and I_γ have extra looping parts, but are in almost the same conformation as I_α.

		Fig. 1 (below). Conformation of Iα in the crystal with one meso-butanetetrol gauche- and trans-conformation labeled (cf. formula on the left; all acetyl groups and hydrogen atoms omitted for clarity).

References

1. L. Kandra, A. Lipták, I. Jodál, P. Nánási, J. Szejtli, J. Incl. Phenom. 1984, 2, 869-875.