Development of Catalysts for the Stereoselective Hydrogenation of α,β-Unsaturated Ketones

Abstract

Iridium phosphinitoxazoline complexes were found to be new efficient catalysts for the asymmetric hydrogenation of arylated α,β-unsaturated ketones. Linear as well as cyclic substrates are hydrogenated with similar success, giving selectivities of up to 99.7% ee.

Pyrrolidine‐Based P,O Ligands from Carbohydrates: Easily Accessible and Modular Ligands for the Ir‐Catalyzed Asymmetric Hydrogenation of Minimally Functionalized Olefins

“…The formation of ligands was confirmed by 31 P { 1 H}, 1 H and 13 C { 1 H} NMR spectra and mass spectrometry. The spectra assignments were supported by the information obtained from 1 HÀ 1 H and 1 HÀ 13 C correlation measurements.…”

“…The reduction of allylic acetates provides a straightforward route to the synthesis of relevant products which are used in the cosmetic industry as components of fragrance mixtures (e. g., Pamplefleur) and also in the pharmaceutical industry (e. g., intermediates for the synthesis of modulators of dopamine D3 receptors). [13] Conclusions New pyrrolidine-based phosphine/phosphite-O/S ligands have been applied in the asymmetric hydrogenation of 32 minimally functionalized olefins. The new ligands are relevant not only because they are easily prepared in a large scale from inexpensive carbohydrates (D-mannose, D-ribose and D-arabinose), but also because they can be easily modulated with a well-established carbohydrate chemistry.…”

“…1 H NMR (300 MHz, CDCl 3 , d ppm) d 1.29 (s, 3H, CH 3 ), 1.42 (s, 3H, CH 3 ), 1.63 (s, 6H, CH 2 , ad), 1.85 (s, 6H, CH 2 , ad), 2.02 (s, 3H, CH, ad), 2.22 (m, 1H, CH 2 ÀP), 2.34 (m, 1H, CH 2 ÀP), 3.29 (m, 1H, CH 2 ÀN), 3.70 (d, 1H, CH 2 ÀN, 2 J HÀH = 12.6 Hz), 4.00 (m, 1H, CHÀN), 4.78 (br.s, 2H, CHÀO), 7.41 (m, 10H, CH=). 13 General procedure for the preparation of the pyrrolidinephosphite ligands L10a-b. The corresponding phosphorochloridite (1.1 mmol) produced in situ was dissolved in toluene (5 mL) and pyridine (3.8 mmol, 0.3 mL) was added.…”

Further Developments and Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

“…Pfaltz discovered an asymmetric hydrogenation of enamines (165) catalyzed by cationic Ir complexes derived from tBu-PHOX (1) (Scheme 45). 59 The level of enantioselectivites observed in these hydrogenations greatly depend on the substitution pattern at the double bond and the nitrogen atom.…”

Asymmetric Hydrogenation of Disubstituted, Trisubstituted, and Tetrasubstituted Minimally Functionalized Olefins and Cyclic β-Enamides with Easily Accessible Ir–P,Oxazoline Catalysts

“…The new Ir-catalyst precursors [Ir­(cod)­( L1 –( L6a–L6h ))]­BAr F , with the P,oxazoline ligands were prepared in few steps from readily available α-acetoxy acids 1 – 3 (see Scheme ). From a common skeleton, several ligand modules can be independently varied to form the family of catalysts. The variations include the following: the substituents and configurations at the ligand backbone (R 1 ); the substituents and configurations at the oxazoline (R 2 ); the substituents and configuration of the biaryl phosphite moiety ( a – e ); and the type of P-donor group (phosphite or phosphinite).…”