Workers at Boehringer Ingelheim have recently published a simple, practical, and scaleable method for preparing N-acetyl enamides. The method is based on a literature method where ketoximes are reductively acetylated with iron powder and acetic anhydride. However this method has the drawback of a variable induction time followed by a fairly vigorous exotherm and a tedious filtration of the iron salts and unreacted iron powder at the end of the reaction.

In the new method the reductive acetylation of ketoximes is carried with Fe(OAc)₂ and acetic anhydride and acetic acid. There is no induction period or sudden exotherm, and at the end of the reaction, which is carried out in THF, you simply add ethyl acetate and water and then separate the layers. The product is in the organic layer and the iron salts stay in the aqueous layer.

15 examples are given with yields varying from 45-90% with the majority being in the range 70-90%.

The products are ideal substrates for asymmetric hydrogenation.

W. Tang,* A. Capacci, M. Sarvestani, X. Wei, N.K. Yee, and C.H. Senanayake (Boehringer Ingelheim), J. Org. Chem., 2009, 74, 9528-9530.