A General Method for the Enantioselective Hydrogenation of β-Keto Esters using Monodentate Binaphthophosphepine Ligands

✍ Scribed by Bernhard Hagemann; Kathrin Junge; Stephan Enthaler; Manfred Michalik; Thomas Riermeier; Axel Monsees; Matthias Beller

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 196 KB
• Volume: 347
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/adsc.200505131

✦ Synopsis

Abstract

17 monodentate phosphepine ligands with a 4,5‐dihydro‐3__H__‐dinaphtho[2,1‐c;1′,2′‐e]phosphepine structural motif have been synthesized and tested in the asymmetric hydrogenation of various β‐keto esters. By variation of the substituents of the aryl group on the phosphorus atom a fine tuning of the selectivity of the catalytic system is possible. Quantitative yield and enantioselectivities up to 95% ee have been achieved for the hydrogenation of methyl acetoacetate (7a), methyl 3‐oxovalerate (7b) and ethyl 4‐phenyl‐3‐oxo‐propionate (7d) using 4‐(4‐methoxyphenyl)‐4,5‐dihydro‐3__H__‐dinaphtho‐[2,1‐c;1′,2′‐e]phosphepine (4g) as ligand. Best enantioselectivities were obtained at comparably high temperatures (100–120 °C), which had the advantage of increased reaction rates.