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Regio- and Stereoselectivity of the SiO2-Catalyzed Reaction of Thiocamphor (= 1,7,7-Trimethylbicyclo[2.2.1]heptane-2-thione) with Optically Active Monosubstituted Oxiranes


Fu, Changchun; Linden, Anthony; Heimgartner, Heinz (2003). Regio- and Stereoselectivity of the SiO2-Catalyzed Reaction of Thiocamphor (= 1,7,7-Trimethylbicyclo[2.2.1]heptane-2-thione) with Optically Active Monosubstituted Oxiranes. Helvetica Chimica Acta, 86:2258-2271.

Abstract

The reactions of the enolizable thioketone (1R,4R)-thiocamphor (= (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]-heptane-2-thione; 1) with (S)-2-methyloxirane (2) in the presence of a Lewis acid such as SnCl4 or SiO2 in anhydrous CH2Cl2 led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(5'), as well as the isomeric beta-hydroxy thioether 5 (Scheme 2). The analogous reactions of 1 with (RS)-, (R)-, and (S)-2-phenyloxirane (7) yielded two isomeric spirocyclic 1,3-oxathiolanes 8 and 9 with Ph at C(4'), an additional isomer 13 bearing the Ph group at C(5'), and three isomeric beta-hydroxy thioethers 10, 11, and 12 (Scheme 4). In the presence of HCl, the beta-hydroxy thioethers 5, 10, 11, and 12 isomerized to the corresponding 1,3-oxathiolanes 3 and 4 (Scheme 3), and 8, 9, and 13, respectively (Scheme 5). Under similar conditions, an epimerization of 3, 8, and 9 occurred to yield the corresponding diastereoisomers 4, 14, and 15, respectively (Schemes 3 and 6). The structures of 9 and 15 were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that the Lewis acid-catalyzed addition of oxiranes to enolizable thioketones proceeds with high regio- and stereo- selectivity via an Sn2-type mechanism.

Abstract

The reactions of the enolizable thioketone (1R,4R)-thiocamphor (= (1R,4R)-1,7,7-trimethylbicyclo[2.2.1]-heptane-2-thione; 1) with (S)-2-methyloxirane (2) in the presence of a Lewis acid such as SnCl4 or SiO2 in anhydrous CH2Cl2 led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(5'), as well as the isomeric beta-hydroxy thioether 5 (Scheme 2). The analogous reactions of 1 with (RS)-, (R)-, and (S)-2-phenyloxirane (7) yielded two isomeric spirocyclic 1,3-oxathiolanes 8 and 9 with Ph at C(4'), an additional isomer 13 bearing the Ph group at C(5'), and three isomeric beta-hydroxy thioethers 10, 11, and 12 (Scheme 4). In the presence of HCl, the beta-hydroxy thioethers 5, 10, 11, and 12 isomerized to the corresponding 1,3-oxathiolanes 3 and 4 (Scheme 3), and 8, 9, and 13, respectively (Scheme 5). Under similar conditions, an epimerization of 3, 8, and 9 occurred to yield the corresponding diastereoisomers 4, 14, and 15, respectively (Schemes 3 and 6). The structures of 9 and 15 were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that the Lewis acid-catalyzed addition of oxiranes to enolizable thioketones proceeds with high regio- and stereo- selectivity via an Sn2-type mechanism.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2003
Deposited On:11 Sep 2013 14:58
Last Modified:07 Dec 2017 22:23
Publisher:Wiley-Blackwell
ISSN:0018-019X
Funders:Swiss National Science Foundation, F. Hoffmann-La roche AG, Basel
Publisher DOI:https://doi.org/10.1002/hlca.200390182

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