N-(2-furylmethyl)benzylamines readily afford palladacycles where the Pd atoms connect to the phenyl ring rather than the furyl ring (Eq. 1.89) (14POL30).

2-(Benzofuran-3-yl)ethanaminium triflate gives the C,N-cyclopalladated cationic complex, which with sodium chloride gives the dinuclear palladium(II) with chloride bridges and with 4-methylpyridine or tert-butylisocyanide the products of ligand exchange (Eq. 1.90) (18OM4648). The chloride bridges in the dimer are split under triphenylphosphine.

The reductive amination of γ- and δ-keto esters or acids with primary amines is a special reaction in which the reductive amination products, N-alkyl γ- or δ-amino esters or acids, tend to cyclize to form the corresponding lactams (Scheme 2) under the reaction conditions.131 The initial reductive amination step is usually fast; however, the cyclization to the lactam takes a longer time. The tandem reaction may be termed a ‘reductive lactamization.’ The reaction provides N-substituted γ-butyrolactams and δ-valerolactams under mild conditions. The reaction was studied for its scope and limitations, and it proved effective primarily for the formation of γ-butyrolactams and δ-valerolactams but not for other lactams.131 Examples of these reactions are listed in Table 6 (entries 7–12). The reductive amination of methyl-5-oxohexanoate and methyl-4-oxopentanoate with benzylamine gave 1-benzyl-6-methylpiperidin-2-one (Table 6, entry 7) and 1-benzyl-5-methylpyrrolidin-2-one (Table 6, entry 8), respectively, in good yields.131 The cyclization was accelerated by warming the reaction to 40–45 °C, but the formation of the γ-butyrolactam was much faster than that of the δ-valerolactam (1.5 h vs. 22 h). Zhang and coworkers130 studied the reductive amination of mucochloric acid with different primary aromatic and aliphatic amines (Table 6, entries 9 and 10). The initial reductive amination products from these reactions cyclize to form the corresponding γ-butyrolactams. Similarly, the reductive amination of o-carboxybenzaldehyde with amines formed the corresponding γ-butyrolactams (Table 6, entries 11 and 12).131 It is interesting to observe that the cyclization of the intermediate from reductive amination of o-carboxybenzaldehyde with 4-aminobutyrate occurs only with the carboxy group to form γ-butyrolactam rather than with the ester to form δ-valerolactam (Table 6, entry 11).