The first Ir-catalyzed asymmetric hydrogenations of vinyl boronates have been performed using low catalyst loadings (0.5 mol%) and pressure (as low as 1 bar). Good selectivities (76-98% ee) were obtained for a range of substrates.

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New chiral bidentate imidazole-phosphine ligands have been prepared and evaluated for the iridium-catalysed asymmetric hydrogenation of olefins. The imidazole-phosphine-ligated iridium catalysts hydrogenated trisubstituted olefins with the same sense of enantiodiscrimination as known iridium catalysts possessing oxazole and thiazole as N-donors.The imidazole-based catalysts were shown to hydrogenate vinyl fluorides, in some cases with the highest ee values published to date.

Diarylmethine-containing stereocenters are present in pharmaceuticals and natural products, making the synthetic methods that form these chiral centers are important in industry. We have applied iridium complexes with novel N,P-chelating ligands to the asymmetric hydrogenation of trisubstituted olefins, forming diarylmethine chiral centers in high conversions and excellent enantioselectivities (up to 99% ee) for a broad range of substrates. Our results support the hypothesis that steric hindrance in one specific area of the catalyst is playing a key role in stereoselection, as the hydrogenation of substrates differing little at the prochiral carbon occurred with high enantioselectivity. As a result, excellent stereodiscrimination was obtained even when the prochiral carbon bore, for example, phenyl and p-tolyl groups.

Fluorine-containing compounds are useful in many applications ranging from pharmaceuticals to ferroelectric crystals. We have developed a new, highly enantioselective synthetic route to trifluoromethyl-bearing stereocenters in up to 96% ee via asymmetric hydrogenation using N,P-ligated iridium catalysts. We also hydrogenated an isomeric mixture of olefins; this reaction gave the hydrogenation product highly enantioselectively (87% ee), and only the E isomer was present after the reaction had reached 56% conversion.Keywords: asymmetric catalysis; fluorine; hydrogenation; iridium; P,N ligands Fluorine-containing compounds are useful in applications ranging from agrochemicals and pharmaceuticals to materials for liquid crystal displays (LCDs). [1] Among the fluoroorganic compounds, trifluoromethyl-substituted molecules have gained much attention, mainly because the electron-withdrawing ability of the trifluoromethyl group can significantly change the physical, chemical and biological properties of a compound. Therefore, much effort has been put towards the synthesis of CF 3 -bearing stereocenters, but their formation is still limited in scope. The existing syntheses of CF 3 -containing chiral centers rely mostly on chemical or biocatalytic resolutions of racemates or on the selective fluorination of chiral, non-fluorinated substrates. [2,3] Chiral Rh and Ru catalysts have been used in the asymmetric hydrogenation of CF 3 -substituted olefins. Because both types of catalysts require a coordinating group near the substrate double bond to obtain high enantioselectivity, all of the trifluoromethyl olefins hydrogenated so far have possessed functionality on or close to the double bond that bears the CF 3 group. In 1980, Koenig et al. reported the first successful asymmetric hydrogenation of a CF 3 -substituted olefin by applying a chiral Rh catalyst in the hydrogenation of 2-acetoxy-3,3,3-trifluoromethyl-1-propene with good enantioselectivity (77%).[4] Ten years later, Burk reported a higher ee (> 95%) for the reduction of the same substrate using Rh catalysts.[5] Kobayashi, Iseki and their co-workers enlarged the scope of functionalized trifluoromethyl olefin hydrogenation using a chiral Ru-(R)-BINAP catalyst.[6] They produced optically active 2-(trifluoromethyl)alkan-1-ols with ee values up to 83% and 2-(trifluoromethyl)propionic acid with 80% ee after derivatization; whereas they hydrogenated an unsaturated CF 3 -substituted ester to an almost racemic product. To the best of our knowledge, there are no routes to obtain simple chiral fluoroalkanes, because all methods give optically active fluoroalkanes with additional functionality.In the past decades, Ir complexes with chiral N,P ligands have proven to be efficient catalysts for the enantioselective hydrogenation of olefins.[7] As these catalysts hydrogenate both unfunctionalized and functionalized olefins, they have an advantage over Rh and Ru catalysts. Since the first chiral mimic of Crabtrees complex was reported by Pfaltz and his coworkers, [8] m...

Hydrogenation O 0220 Iridium Catalysts with Chiral Imidazole-Phosphine Ligands for Asymmetric Hydrogenation of Vinyl Fluorides and other Olefins. -The novel imidazole-based catalysts are used in asymmetric hydrogenation of trisubstituted olefins and even of vinyl fluorides. -(KAUKORANTA, P.; ENGMAN, M.; HEDBERG, C.; BERGQUIST, J.; ANDERSSON*, P. G.; Adv. Synth. Catal. 350 (2008) 7-8, 1168-1176; Dep. Biochem., Uppsala Univ., S-751 23 Uppsala, Swed.; Eng.) -Nuesgen 39-036

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