Hydrogenation of cyclic imines

Scheme 8.5 Buchwald s example of asymmetric hydrogenation of cyclic imine.

As illustrated in the hydrogenation of cyclic imines, the system is compatible with a wide range of functional groups, such as olefins, protected or unpro-... 

Table 6.5 Enantioselective hydrogenation of cyclic imines catalyzed by [(R,R,R)-(EBTHI)TiX2],...

Table 34.5 Selected results for the enantioselective hydrogenation of cyclic imines (for structures, see Fig. 34.8) Catalytic system, reaction conditions, enantioselectivity, productivity and activity.

A water-soluble, recyclable ruthenium(II) complex including a chiral diamine ligand has been used for asymmetric transfer hydrogenation of cyclic imines and iminiums in water, with yields and ee up to 99%.49... 

The Pictet-Spengler reaction, the cyclization of an electron-rich aryl or heteroaryl group onto an imine electrophile, is the established method for the synthesis of tetrahydroisoquinoline and tetrahydro-/ -carboline ring systems. Catalytic asymmetric approaches to these synthetically important structures are mostly restricted to asymmetric hydrogenations of cyclic imines [77, 78]. In a noteworthy... 

Asymmetric hydrogenation of cyclic imine 8 using two mol % of chiral Ru-complex 9 in a formic acid-triethylamine mixture, as developed by Noyori and co-workers, results in the desired stereoisomer 10 with an excellent optical purity of 97 %... 

R1 Catalytic Asymmetric Hydrogenation of Cyclic Imines. 

F. 8 Synthetic targets prepared by asymmetric transfer hydrogenation of cyclic imines... 

Morimoto, T. Achiwa, K. An improved diphosphine-iridium(I) catalyst system for the asymmetric hydrogenation of cyclic imines Phthalimide as an efficient co-catalyst. Tetrahedron Asymmetry 1995, 6,2661-2664. 

SCHEME 30.38. Enantioselective hydrogenation of cyclic imines 195 and 197 in the total syntheses of (7 )-levofloxacin and (N)-calycotomine, respectively. 

Morimoto and co-workers reported on the total synthesis of the optically active 1-hydroxymethyl-substituted tetrahydroisoquinoUne alkaloid (S)-calycotoinine employing the Ir-catalyzed asymmetric hydrogenation of cyclic imine 197 (Scheme 30.38). Iridium(I)-(/ )-BINAP-F4-phthaUmide complex (0.5 mol%) has been used as a chiral catalyst, and hydrogenation was accomplished in tolue-ne/MeOH mixture under 100 atm at 2°C to 5°C to furnish (5)-198 in 85% yield and 86% ee. 

Several approaches toward the syntheses of quinolacta-cins were published. ° In 2008, Silva Santos and coworkers applied Noyori asymmetric transfer hydrogenation of cyclic imine 218 to the total synthesis of (5)-(—)-quinolactacin B, which showed activity against mmor necrosis factor production. The hydrogenation of imine 218 was accomplished with the (/ ,/ )-Ts-DPEN-Ru(ll) complex in DMF and a HC02H/Et3N mixture to obtain amine (5)-(—)-219 in 89% yield and >90% ee (Scheme 30.43). 

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