How to Tantalise Your Reactions?

When secondary and tertiary amines are made by alkylation, the halide waste leads to poor atom economy; reductive alkylation using aldehydes and ketones is usually a more attractive method, both from a selectivity and atom economy viewpoint.

Industrially amines can also be made by reaction of an amine with an alcohol in the presence of a nickel catalyst (via an oxidation-reduction sequence), but this is not general.  Addition of amines to olefins (hydroamination) is an atom efficient method and several groups have recently reported success in this field.  Now, the group of Hartwig at Illinois has reported the use of tantalum catalysts to add amines, using the a C-H bond, across olefins to give a new synthesis of amines.  (Herzon S B et al, J Am Chem Soc, 2007, 129, 6690-6691).

Although there were earlier reports of this reaction over 20 years ago, the yields were poor to moderate.  Hartwig’s group has found new catalysts which make the reaction synthetically useful and possibly industrially attractive.

Aryl alkyl amines give higher yields than dialkyl-amines.  This may be because the mechanism may involve metalation of the aromatic ring at some stage.  Deuteriation studies indicate that D is incorporated in the ortho position, but that this intermediate may not be on the direct reaction pathway.



Trevor Laird