A Convenient Route to (E)-α,β-Unsaturated Methyl Ketones

Abstract

Aldehydes are converted into (E)-α,β-unsaturated methyl ketones in good yield and with a high E stereoselectivity using α,α-bis(trimethylsilyl) N-tert-butyl acetimine 3. The reaction was mediated by a catalytic amount of tetrabutylammonium fluoride (TBAF) under mild conditions. The disilylated reagent 3 is easily generated from N-tert-butylacetimine, lithium diisopropylamide (LDA), and chlorotrimethylsilane. The mechanism of the reaction is discussed.

Keywords:

• LDA
• α-silylated acetimines
• TBAF
• N-tert-butylacetimine
• α,β-unsaturated methyl ketones

Notes

^a Estimated by ¹H NMR on the crude reaction mixture with respect to nonreacted benzaldehyde (molar percentage).

^b The stereoselectivity of the compound 4a is determined by the ¹H NMR spectrum of the crude product.

^a Isolated yield.

^b The stereoselectivity of each compound is determined by the ¹H NMR spectrum of the crude product.