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Lewis acid catalyzed reactions of thioketones with 1,2-epoxycyclohexane and 1,2-epoxycyclopentane


Blagoev, Milen; Linden, Anthony; Heimgartner, Heinz (1999). Lewis acid catalyzed reactions of thioketones with 1,2-epoxycyclohexane and 1,2-epoxycyclopentane. Helvetica Chimica Acta, 82:2316-2335.

Abstract

Non-enolizable thioketones and 1,2-epoxycycloalkanes undergo a Lewis acid catalyzed addition reaction to give 1,3-oxathiolanes. Appropriate reaction conditions are CH2Cl2 as the solvent, BF 3.Et2O as the Lewis acid, and a temperature between -78° and r.t. Under the reaction conditions, the 1,3-oxathiolanes are only moderately stable. They decompose to yield the corresponding epithiocycloalkane and ketone. In general, 1,3- dithiolanes are isolated as minor products or, after prolonged reaction, as the main product. These secondary products are formed via the Lewis acid catalyzed reaction of the intermediate epithiocycloalkane and a second molecule of the thioketone. In the reaction of thiobenzophenone and 1,2-epoxycyclohexane, trans-8,8-diphenyl-7,9-dioxabicyclo[4.3.0]nonane is formed in small amounts as an additional side product (Scheme 12). In all cases, the newly formed heterocycle and the carbocycle are trans-fused. This result is consistent with a nucleophilic ring-opening of the complexed oxirane by the thioketone via inversion of the configuration and subsequent formation of the O(1)-C(2) bond of the 1,3-oxathiolane (Scheme 13). The surprising formation of the fused 1,4-oxathiepan derivative 23 (Scheme 9) is in accordance with an ionic reaction mechanism (cf. Scheme 15).

Non-enolizable thioketones and 1,2-epoxycycloalkanes undergo a Lewis acid catalyzed addition reaction to give 1,3-oxathiolanes. Appropriate reaction conditions are CH2Cl2 as the solvent, BF 3.Et2O as the Lewis acid, and a temperature between -78° and r.t. Under the reaction conditions, the 1,3-oxathiolanes are only moderately stable. They decompose to yield the corresponding epithiocycloalkane and ketone. In general, 1,3- dithiolanes are isolated as minor products or, after prolonged reaction, as the main product. These secondary products are formed via the Lewis acid catalyzed reaction of the intermediate epithiocycloalkane and a second molecule of the thioketone. In the reaction of thiobenzophenone and 1,2-epoxycyclohexane, trans-8,8-diphenyl-7,9-dioxabicyclo[4.3.0]nonane is formed in small amounts as an additional side product (Scheme 12). In all cases, the newly formed heterocycle and the carbocycle are trans-fused. This result is consistent with a nucleophilic ring-opening of the complexed oxirane by the thioketone via inversion of the configuration and subsequent formation of the O(1)-C(2) bond of the 1,3-oxathiolane (Scheme 13). The surprising formation of the fused 1,4-oxathiepan derivative 23 (Scheme 9) is in accordance with an ionic reaction mechanism (cf. Scheme 15).

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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:1999
Deposited On:05 Nov 2013 16:34
Last Modified:05 Apr 2016 17:06
Publisher:Wiley-Blackwell
ISSN:0018-019X
Funders:Swiss National Science Foundation, F. Hoffmann-La Roche AG, Basel
Publisher DOI:https://doi.org/10.1002/(SICI)1522-2675(19991215)82:12<2316::AID-HLCA2316>3.0.CO;2-3
Permanent URL: https://doi.org/10.5167/uzh-84352

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