Metal-Free, One-Pot, Sequential Protocol for-Transforming α,β-Epoxy Ketones to β-Hydroxy Ketones and α-Methylene Ketones

A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to beta-hydroxy ketones and alpha-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate ((BF3OEt2)-O-.) 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 beta-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 alpha-methylene ketone products can be carried out in one pot.