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1,5-Dipolare Elektrocyclisierung von Acyl-substituierten ‘Thiocarbonyl-yliden’ zu 1,3-Oxathiolen


Kägi, Martin; Linden, Anthony; Mloston, Grzegorz; Heimgartner, Heinz (1996). 1,5-Dipolare Elektrocyclisierung von Acyl-substituierten ‘Thiocarbonyl-yliden’ zu 1,3-Oxathiolen. Helvetica Chimica Acta, 79(3):855-874.

Abstract

The reaction of alpha-diazoketones 15a,b with 4,4-disubstituted 1,3-thiazole-5(4H)-thiones 6 (Scheme 3), adamantanethione (17), 2,2,4,4-tetramethyl-3-thioxocyclobutanone (19; Scheme 4), and thiobenzophenone (22; Scheme 5), respectively, at 50-90° gave the corresponding 1,3-oxathiole derivatives as the sole products in high yields. This reaction opens a convenient access to this type of five-membered heterocycles.The structures of three of the products, namely 16c, 16f, and 20b, were established by X-ray crystallography. The key-step of the proposed reaction mechanism is a 1,5-dipolar electrocyclization of an acyl-substituted ‘thiocarbonyl-ylide’ (cf. Scheme 6). The analogous reaction of 15a,b with 9H-xanthen-9-thione (24a) and 9H-thioxanthen-9-thione (24b) yielded alpha,beta-unsaturated ketones of type 25 (Scheme 5). The structures of 25a and 25c were also established by X-ray crystallography. The formation of 25 proceeds via a 1,3-dipolar electrocyclization to a thiirane intermediate (Scheme 6 ) and desulfurization. From the reaction of 15a with 24b in THF at 50°, the intermediate 26 (Scheme 5) was isolated. In the crude mixtures of the reactions of 15a with 17 and 19, a minor product containing a CHO group was observed by IR and NMR spectroscopy. In the case of 19, this side product could be isolated and was characterized by X-ray crystallography to be 21 (Scheme 4). It was shown that 21 is formed - in relatively low yield - from 20a. Formally, the transformation is an oxidative cleavage of the C=C bond, but the reaction mechanism is still not known.

Abstract

The reaction of alpha-diazoketones 15a,b with 4,4-disubstituted 1,3-thiazole-5(4H)-thiones 6 (Scheme 3), adamantanethione (17), 2,2,4,4-tetramethyl-3-thioxocyclobutanone (19; Scheme 4), and thiobenzophenone (22; Scheme 5), respectively, at 50-90° gave the corresponding 1,3-oxathiole derivatives as the sole products in high yields. This reaction opens a convenient access to this type of five-membered heterocycles.The structures of three of the products, namely 16c, 16f, and 20b, were established by X-ray crystallography. The key-step of the proposed reaction mechanism is a 1,5-dipolar electrocyclization of an acyl-substituted ‘thiocarbonyl-ylide’ (cf. Scheme 6). The analogous reaction of 15a,b with 9H-xanthen-9-thione (24a) and 9H-thioxanthen-9-thione (24b) yielded alpha,beta-unsaturated ketones of type 25 (Scheme 5). The structures of 25a and 25c were also established by X-ray crystallography. The formation of 25 proceeds via a 1,3-dipolar electrocyclization to a thiirane intermediate (Scheme 6 ) and desulfurization. From the reaction of 15a with 24b in THF at 50°, the intermediate 26 (Scheme 5) was isolated. In the crude mixtures of the reactions of 15a with 17 and 19, a minor product containing a CHO group was observed by IR and NMR spectroscopy. In the case of 19, this side product could be isolated and was characterized by X-ray crystallography to be 21 (Scheme 4). It was shown that 21 is formed - in relatively low yield - from 20a. Formally, the transformation is an oxidative cleavage of the C=C bond, but the reaction mechanism is still not known.

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Additional indexing

Other titles:1,5-Dipolar Electrocyclization of Acyl-Substituted ‘Thiocarbonyl-ylides’ to 1,3-Oxathioles
Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:German
Date:1996
Deposited On:25 Nov 2013 08:25
Last Modified:05 Apr 2016 17:11
Publisher:Wiley-Blackwell
ISSN:0018-019X
Funders:Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung, F. Hoffmann-La Roche AG, Basel
Publisher DOI:https://doi.org/10.1002/hlca.19960790327

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