Abstract
The substitution of a siloxy group using thiosilanes smoothly occurred in the presence of InI3 catalyst to yield the corresponding thioethers. InI3 was a specifically effective catalyst in this reaction system, while other typical Lewis acids such as BF3·OEt2, AlCl3, and TiCl4 were ineffective. Various silyl ethers such as primary alkyl, secondary alkyl, tertiary alkyl, allylic, benzylic, and propargylic types were applicable. In addition, bulky OSitBuMe2 and OSiiPr3 groups, other than the OSiMe3 group, were successfully substituted. The substitution reaction of enantiopure secondary benzylic silyl ether yielded the corresponding racemic thioether product, which suggested that the reaction of tertiary alkyl, secondary alkyl, benzylic, and propargylic silyl ethers would proceed via a SN1 mechanism.
Highlights
Organosulfur compounds are important building blocks in organic synthesis because many natural and pharmaceutical products contain sulfur [1,2,3,4,5]
The substitution reaction of alkyl halides with sulfur nucleophiles is one of the most typical and practical methods in the synthesis of alkyl thioethers (Scheme 1A) [13,14,15,16,17,18]
In general, a multi-step sequence involving deprotection and transformation of the siloxy group is required in order to transform silyl ethers to thioethers (Scheme 1B)
Summary
Organosulfur compounds are important building blocks in organic synthesis because many natural and pharmaceutical products contain sulfur [1,2,3,4,5]. The use of alkyl halides has an inherent problem; that is, the potential toxicity of alkyl halides and metal halides as by-products Alcohol derivatives such as alkyl ethers, alkyl acetates, alkyl carbonates, and silyl ethers have been suggested as promising substrates that could solve the problem. Silyl ethers are one of the most useful alcohol derivatives because they are often used as protected alcohols in the syntheses of complex organic compounds such as natural products, drugs, and agrichemicals [19,20]. There are few reports about the synthesis of thioethers via the direct use of silyl ethers, due to the very poor leaving ability of the siloxy group [21]. We report the direct substitution of a siloxy group with thiosilanes catalyzed by InI3 to synthesize a Molecules 2016, 21, 1330; doi:10.3390/molecules21101330 www.mdpi.com/journal/molecules
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