Asymmetrische reduktive Aminierung von Cycloalkanonen, 5. Synthese und absolute Konfiguration 2‐substituierter Cyclopentanamine

Asymmetric Reductive Amination of Cycloalkanones, 5. Synthesis and Absolute Configuration of 2‐Substituted Cyclopentanamines In an asymmetric synthesis 2‐substituted cyclopentanamines are obtained from racemic cyclopentanones by means of reductive amination in a three‐step procedure. Condensation of the ketones 3(n) with optically active 1‐phenylethylamines yields imine mixtures 4(n), which are hydrogenated with Raney nickel to give the optically active, diastereomerically pure secondary amines 5(n). Hydrogenolysis with Palladium‐on‐charcoal leads to high grade enantiomerically pure primary amines 6(n) with good yields. The relative configuration of the amines 5(n) and 6(n) is elucidated by 1H and 13C NMR techniques. The absolute configuration is determined by X‐ray analysis of the 4‐bromobenzamide 8 of the primary amine (+)‐6(n)e and with the help of CD of the salicylidenes 9(n). The kinetically controlled asymmetric hydrogenation with a first order transformation as proved reaction mechanism in the cyclohexanamine line is confirmed for this investigation. The hydrogenation runs like‐induced to the cis‐configurated amines 5(n) and 6(n), respectively.