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Metal-Free, One-Pot, Sequential Protocol for Transforming α,β-Epoxy Ketones to β-Hydroxy Ketones and α-Methylene Ketones
- Hasegawa, Eietsu, Arai, Saki, Tayama, Eiji, Iwamoto, Hajime
- Journal of organic chemistry 2015 v.80 no.3 pp. 1593-1600
- boron, cations, chemical reactions, chemical structure, chlorides, epoxides, hydrides, ketones, organic chemistry, regioselectivity, triethylamine
- A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to β-hydroxy ketones and α-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate (BF₃·OEt₂) generates the cationic intermediates by regioselective epoxide ring opening and an acyl shift. Then, a treatment of these cations with 2-aryl-1,3-dimethylbenzimidazolines (DMBIH) results in formation of 1,2-disubstituted 3-hydroxy ketones. DMBIH serves as a hydride donor in the second step of this process. Finally, the β-hydroxy ketones can be converted to 1,2-disubstituted 2-methylene ketones by treatment with methanesulfonic acid or a combination of methanesulfonyl chloride and triethylamine. Importantly, the sequential steps involved in formation of the α-methylene ketone products can be carried out in one pot.