Transamination, metal-free

In some cases, the function of the metal ion is more to deactivate alternative sites of reaction than to activate a particular atom towards attack by an electrophile. A good example of this is seen in the transamination reaction of ornithine (5.12) with urea. Co-ordination of the ornithine to copper(n) results in the formation of a five-membered chelate ring, leaving the amino group of the 3-aminopropyl substituent as the most nucleophilic site in the complex. Reaction of this complex with urea results in a transamination process and the formation of the copper(n) complex of the substituted urea, which is the amino acid citrulline (5.13) (Fig. 5-20). The complex may be demetallated to yield the free amino acid in respectable yields. 

Several routes to Mg bisamides have been developed. These include the direct reaction between the metal and a protic amine, a variety of transmetalation strategies, disproportionation of alkylmagnesium amides, and transamination reactions (Scheme 3.32). On the other hand, the most straightforward and most routine synthesis involves the reaction of a dialkylmagnesium with two equivalents of amine. In some instances the amination reaction ceases after transfer of one amino function but gentle heating of the reaction mixture is usually sufficient to ensure complete conversion to the bisamide. Without doubt this route is now the method of choice, because ether-free Bu2Mg (supplied as a 1 1 mixture of n- and s-butyl, with 5% n-octyl, in heptane) has become commercially available (Aldrich). 

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