Synthesis of ferrocenyl-substituted 1,3-dithiolanes via [3 + 2]-cycloadditions of ferrocenyl hetaryl thioketones with thiocarbonylS-methanides

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Abstract
Ferrocenyl hetaryl thioketones react smoothly with in situ generated thiocarbonylS-methanides to give 1,3-dithiolanes. In the case of aromaticS-methanides, the sterically more crowded 4,4,5,5-tetrasubstituted 1,3-dithiolanes (2-CH2isomers) were formed as sole products. The reactions with cycloaliphaticS-methanides led to mixtures of 2-CH2and 5-CH2isomers with the major component being the sterically more crowded 2-CH2isomers. 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.

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