Highly Enantioselective Direct Synthesis of Endocyclic Vicinal Diamines through Chiral Ru(diamine)‐Catalyzed Hydrogenation of 2,2′‐Bisquinoline Derivatives

Abstract

An asymmetric hydrogenation of 2,2'-bisquinoline and bisquinoxaline derivatives, catalyzed by chiral cationic ruthenium diamine complexes, was developed. A broad range of chiral endocyclic vicinal diamines were obtained in high yields with excellent diastereo- and enantioselectivity (up to 93:7 dl/meso and >99 % ee). These chiral diamines could be easily transformed into a new class of chiral N-heterocyclic carbenes (NHCs), which are important but difficult to access.

Applications of N′-monofunctionalised TsDPEN derivatives in asymmetric catalysis

“…Fan et al also reported the asymmetric hydrogenation of 2,2'-bisquinolines to form vicinal diamines using a series of [arene/Ru/TsDPEN] catalysts including 14-16 [21] (Figure 11). In several cases, the N'-methylated catalyst proved to be the best one in the application, although in others the unmethylated complex was better.…”

Consecutive Intermolecular Reductive Amination/Asymmetric Hydrogenation: Facile Access to Sterically Tunable Chiral Vicinal Diamines and N‐Heterocyclic Carbenes

“…Asymmetric hydrogenation has proven to be one of the most powerful methods for the preparation of various chiral amines . However, examples of the direct synthesis of chiral vicinal diamines by catalytic asymmetric hydrogenation are extremely rare . Previously, we demonstrated that the cationic ruthenium or iridium complexes of chiral monosulfonated diamines are excellent catalysts in the asymmetric hydrogenation of quinoline derivatives and ketimines .…”

“…Such chiral NHCs could be readily accessed through the direct derivatization of vicinal diamines –. However, to the best of our knowledge, the direct catalytic asymmetric synthesis of sterically hindered N , N′ ‐diaryl vicinal diamines has not been achieved …”

“…Previously, we demonstrated that the cationic ruthenium or iridium complexes of chiral monosulfonated diamines are excellent catalysts in the asymmetric hydrogenation of quinoline derivatives and ketimines . Later, this catalytic system was successfully applied to the asymmetric hydrogenation of 2,2′‐bisquinoline derivatives, affording direct access to chiral endocyclic vicinal diamines . However, this method suffered from difficulties in substrate synthesis and low stereoselectivity for sterically hindered substrates.…”

A diversity of recently reported methodology for asymmetric imine reduction

“…A novel method to obtain optically pure chiral endocyclic vicinal diamines have been demonstrated by Fan and coworkers. 34 In this protocol, the chiral cationic ruthenium diamine catalyst 19 has been applied to the AH of 2,2′-bisquinoline and 2,2′-bisquinoxaline derivatives to give the corresponding chiral amines in good diastereoselectivity (up to 93 : 7) and excellent enantioselectivity (>99% ee) ( Fig. 29).…”