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Molecules 2016, 21(11), 1503; doi:10.3390/molecules21111503

Double Intramolecular Transacetalization of Polyhydroxy Acetals: Synthesis of Conformationally-Restricted 1,3-Dioxanes with Axially-Oriented Phenyl Moiety

1
Institut für Pharmazeutische und Medizinische Chemie der Westfälischen Wilhelms-Universität Münster, Corrensstraße 48, D-48149 Münster, Germany
2
Cells-in-Motion Cluster of Excellence (EXC 1003–CiM), Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Diego Muñoz-Torrero
Received: 14 October 2016 / Revised: 31 October 2016 / Accepted: 3 November 2016 / Published: 9 November 2016
(This article belongs to the Section Medicinal Chemistry)
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Abstract

The synthesis of conformationally-restricted 1,3-dioxanes with a phenyl moiety fixed in an axial orientation at the acetalic center is described. Starting with diethyl 3-hydroxyglutarate (15), benzaldehyde acetal 12a and acetophenone ketal 12b bearing a protected 1,3,5-trihydroxypentyl side chain in the o-position were prepared. The first acid-catalyzed intramolecular transacetalization gave a mixture of diastereomeric 2-benzofurans 18 (ratio of diastereomers 2:2:1:1). After OH group deprotection, the second intramolecular transacetalization afforded tricyclic alcohol 14a (2-(1,5-epoxy-1,3,4,5-tetrahydro-2-benzoxepin-3-yl]ethan-1-ol). Analogous cyclizations led to the corresponding silyl ether 22a (19%) and azide 23a (13%). Whereas tricyclic alcohol 14a was obtained as a 1:1 mixture of diastereomers, the silyl ether 22a and the azide 23a afforded only one diastereomer. This observation indicates a faster cyclization of the minor diastereomers providing the thermodynamically-favored compounds with equatorially-oriented substituents in the 3-position of the tricyclic 1,5-epoxy-2-benzoxepine system. In general, acetophenone-derived ketalic compounds (b-series) required very mild reaction conditions and gave lower yields than the corresponding acetalic compounds (a-series). View Full-Text
Keywords: double intramolecular transacetalization; polyhydroxy acetals; conformationally-restricted 1,3-dioxanes; axially-oriented phenyl moiety; tricyclic alcohols; 1,5-epoxy-2-benzoxepines double intramolecular transacetalization; polyhydroxy acetals; conformationally-restricted 1,3-dioxanes; axially-oriented phenyl moiety; tricyclic alcohols; 1,5-epoxy-2-benzoxepines
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Asare-Nkansah, S.; Wünsch, B. Double Intramolecular Transacetalization of Polyhydroxy Acetals: Synthesis of Conformationally-Restricted 1,3-Dioxanes with Axially-Oriented Phenyl Moiety. Molecules 2016, 21, 1503.

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