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Synthesis of ferrocenyl-substituted 1,3-dithiolanes via [3 + 2]-cycloadditions of ferrocenyl hetaryl thioketones with thiocarbonyl S -methanides
ABSTRACT
Ferrocenyl hetaryl thioketones react smoothly with in situ generated thiocarbonyl S-methanides to give 1,3-dithiolanes. In the case of aromatic S-methanides, the sterically more crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes (2-CH2 isomers) were formed as sole products. The reactions with cycloaliphatic S-methanides led to mixtures of 2-CH2 and 5-CH2 isomers with the major component being the sterically more crowded 2-CH2 isomers. The preferred formation of the latter products is explained by the assumption that the formal [3 + 2]-cycloadducts were formed via a stepwise reaction mechanism with a stabilized 1,5-diradical as a key intermediate. The complete change of the reaction mechanism toward the concerted [3 + 2]-cycloaddition was observed in the reaction of a sterically crowded cycloaliphatic thiocarbonyl ylide with ferrocenyl methyl thioketone. No MeSH data available. |
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C1: Reactions of aromatic thiocarbonyl S-methanides 2a,b with ferrocenyl thioketones 1 (Table 1). Mentions: The precursors of aromatic S-methanides 2a,b, i.e., 1,3,4-thiadiazolines 3a,b, were prepared from thiobenzophenone (4a) and thiofluorenone (4b), respectively, and diazomethane at –60 °C in THF solution [6] (Scheme 1). After addition of an equimolar amount of a ferrocenyl hetaryl thioketone 1, the reaction mixture was slowly warmed to room temperature. The crude mixture was examined by 1H NMR spectroscopy, and in all cases only one single product 5 was detected (Table 1). |
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Ferrocenyl hetaryl thioketones react smoothly with in situ generated thiocarbonyl S-methanides to give 1,3-dithiolanes. In the case of aromatic S-methanides, the sterically more crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes (2-CH2 isomers) were formed as sole products. The reactions with cycloaliphatic S-methanides led to mixtures of 2-CH2 and 5-CH2 isomers with the major component being the sterically more crowded 2-CH2 isomers. The preferred formation of the latter products is explained by the assumption that the formal [3 + 2]-cycloadducts were formed via a stepwise reaction mechanism with a stabilized 1,5-diradical as a key intermediate. The complete change of the reaction mechanism toward the concerted [3 + 2]-cycloaddition was observed in the reaction of a sterically crowded cycloaliphatic thiocarbonyl ylide with ferrocenyl methyl thioketone.
No MeSH data available.
