A Highly Enantioselective, Pd–TangPhos‐Catalyzed Hydrogenation of <i>N</i>‐Tosylimines

“…In 1990, Oppolzer et al 1a first reported the asymmetric hydrogenation of cyclic N-sulfonylimines by using Ru catalysts with up to 99% ee after crystallization. Recently, Zhang et al 4 described a Pd-catalyzed asymmetric hydrogenation of a cyclic N-sulfonylimine with high enantioselectivity. However, for the above-reported catalytic systems, only one substrate derived from saccharin was reported.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Hydrogenation of Cyclic N‐Sulfonylimines with Phosphine‐Free Chiral Cationic Ru‐MsDPEN Catalysts

Chen

et al. 2010

Chin. J. Chem.

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“…The first hydrogenation of imino esters catalyzed by palladium complexes was described by Amii [10] and coworkers with up to 91% ee in 2001. Afterwards, highly enantioselectively Pd-catalyzed hydrogenations of N-diphenylphosphinyl ketimines and N-tosylimines were reported by us [11] and the Zhang [12] group, respectively [Scheme 1, Eq. (1)].…”

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confidence: 99%

“…MeOH and CH 2 Cl 2 led to very low reactivity (entries 13 and 14); TFE was found to be the optimal solvent, which is in accordance with the Pd-catalyzed hydrogenation of ketones and activated imines in the literature. [8][9][10][11][12][13][14][15][16] Subsequently, some commercially available bisphosphine ligands were examined under the above conditions. The results showed that axial chiral bidentate bisphosphine ligands L1-L4 and L6-L8 (Table 2, entries 1-4 and 6-8) gave full conversions with 58-75% ee.…”

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confidence: 99%

“…Interestingly, this catalytic system is particularly effective for the asymmetric hydrogenation of cyclic ketA C H T U N G T R E N N U N G imines 1j-1o derived from the cyclic ketone, 1-tetralone, 88-95% ees were achieved (Table 3, en- tries [10][11][12][13][14][15]. For the cyclic imines 2p-2s derived from 4-chromanone, 86-93% ee were obtained under the standard conditions (entries [16][17][18][19].…”

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confidence: 99%

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Palladium‐Catalyzed Asymmetric Hydrogenation of Simple Ketimines Using a Brønsted Acid as Activator

2010

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Using a catalytic amount of a Brønsted acid as activator of simple imines, the highly enantioselective homogeneous palladium-catalyzed asymmetric hydrogenation of simple ketimines was successfully developed with up to 95% ee.Keywords: asymmetric hydrogenation; Brønsted acids; ketimines; palladium catalysisThe preparation of chiral amines from the transition metal-catalyzed asymmetric hydrogenation or transfer hydrogenation of prochiral imines represents one of the most direct and efficient approaches that open a straightforward route to valuable building blocks for natural products, pharmaceuticals and other fine chemical compounds.[1] A variety of chiral metal catalysts has been successfully applied to this reaction over the last few decades. Among the various catalytic systems so far, Ru, [2] Rh, [3] Ir [4] and organocatalysts [5] have been successfully employed in enantioselective hydrogenations and/or transfer hydrogenations of imines. Recently, Zhang and co-workers developed the first asymmetric hydrogenation of unprotected N À H iminiums with up to 95% ee using chiral iridium complexes as catalyst.[6] Although significant progress have been made in the enantioselective reduction of imines, the search for new catalytic systems is still highly desirable.Pd-based catalytic systems have been extensively employed for a wide range of useful synthetic organic transformations, [7] nevertheless, very little attention has been paid to homogeneous asymmetric hydrogenation with chiral Pd complexes. The asymmetric hydrogenations of a-phthalimide ketones and a-keto phosphonates with palladium catalyst systems were reported by us [8] and Goulioukina, [9] respectively. In comparison, there are more reports on Pd-catalyzed asymmetric hydrogenations of activated imines. The first hydrogenation of imino esters catalyzed by palladium complexes was described by Amii [10] and coworkers with up to 91% ee in 2001. Afterwards, highly enantioselectively Pd-catalyzed hydrogenations of N-diphenylphosphinyl ketimines and N-tosylimines were reported by us [11] and the Zhang [12] group, respectively [Scheme 1, Eq. (1)]. Since then, chiral palladium complexes have also been employed for the asymmetric hydrogenation of some other cyclic activated sulfonylimines in our laboratory. [13] In 2009, Rubio-PØrez [14] and co-workers reported the direct reductive amination of alkyl ketones catalyzed by chiral palladium complexes at 70 8C with up to 99% ee, but only moderate yield and low enantiomeric excess were observed in the amination of aryl ketones. Most recently, an efficient Pd-catalyzed asymmetric hydrogenation of simple indoles was developed by us with a Brønsted acid as activator.[15] Although much effort Scheme 1. Activation strategy for Pd-catalyzed asymmetric hydrogenation of simple ketimines.

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A Highly Enantioselective, Pd–TangPhos‐Catalyzed Hydrogenation of N‐Tosylimines

Cited by 186 publications

References 55 publications

Palladium-catalyzed asymmetric hydrogenation of simple ketones activated by Brønsted acids

Palladium-catalyzed asymmetric hydrogenation of simple ketones activated by Brønsted acids

Asymmetric Hydrogenation of Cyclic N‐Sulfonylimines with Phosphine‐Free Chiral Cationic Ru‐MsDPEN Catalysts

Palladium‐Catalyzed Asymmetric Hydrogenation of Simple Ketimines Using a Brønsted Acid as Activator

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