N-Alkyl Imines

The nature of the substituent directly attached to the N-atom influences the properties (basicity, reduction potential, etc.) of the C = N function more than the substituents at the carbon atom. For example, it was found that Ir-dipho-sphine catalysts that are very active for N-aryl imines are deactivated rapidly when applied for aliphatic imines [7], or that titanocene-based catalysts are active only for N-alkyl imines but not for N-aryl imines [8, 20, 21]. Oximes and other C = N-X compounds show even more pronounced differences in reactivity. 

Until now, few acyclic N-alkyl imines or the corresponding amines have been found to be of practical industrial importance. Most studies reported herein were carried out with model substrates, especially with the N-benzyl imine of acetophenone 5a and some analogues thereof (Fig. 34.7). One reason for this choice could be the easy preparation of a pure crystalline starting material, and another reason might be that the chiral primary amines can be obtained by hy-drogenolysis of the benzyl group. As can be seen in Table 34.4, there are several catalyst systems with fair to good ee-values and activities. 

Table 34.4 Selected results for the enantioselective hydrogenation of N-alkyl imines and enamines (for structures, see Fig. 34.7) Catalytic system, reaction conditions, enantioselectivity, productivity and activity.

Beim Kochen der prim. Amine mit Braunstein in 1,4-Dioxan unter Stickstoff erhalt man die N-Alkyl-imine der dem eingesetzten Alkyl-Rest entsprechenden Aldehyde97 ... 

Palladium-Katalysatoren hydrieren N-Alkyl-imine aromatischer Aldehyde bei 14—45°/l—4 bar ebenfalls zu sekundaren Aminen z.B. ... 

Hydrogenation of unfunctionalized C=C Hydrogenation of a- or 8-functionalized C=0 Hydrogenation of aryl ketones Hydrogenation of unfunctionalized C=0 Hydrogenation of N-aryl or cyclic imines Hydrogenation of N-alkyl imines Hydrogenation of N-acyl-hydrazones Epoxidation of allylic alcohols Epoxidation of C=C... 

Cho and Chun reported an effective stoichiometric reduction of aromatic ketone N-phenylimines 63 using la-BHj or Za BHj to give the desired N-phenylamine 64 with good enantioselectivities (Table 11.10) [87]. The reduction was also effective when 0.1 equiv of la or 2a was used (runs 2 and 4). BHj THF as borane reagent in this reduction led to the J amine, whereas CB furnished the S amine (runs 8 and 9) [88]. For N-alkyl imine analogues, the reduction of N-tert-butyl imine of acetophenone provided 80% ee (run 12). However, reductions of other N-alkyl imine derivatives of the same ketone (runs 10, 11, 13 and 17) and N-phenyl or N-alkyl imine derivatives of... 

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