Evaluation of calix[4]arene-based chiral diphosphite ligands in Rh-catalyzed asymmetric hydrogenation of simple dehydroamino acid derivatives

✍ Scribed by Shasha Liu; Christian A. Sandoval

• Book ID: 104059268
• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 657 KB
• Volume: 325
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/j.molcata.2010.03.034

✦ Synopsis

The calix [4]arene framework was readily modified to generate a number of chiral BINOL-based diphosphite ligands (3) capable of forming in situ Rh-complexes which catalyzed the asymmetric hydrogenation of model substrates methyl-(Z)-2-(acetamido)acrylate (1a) and methyl-(Z)-2-(acetamido)cinnamate (1b). The (S,S)-catalyst generated the (R)-product. Upper rim (R 1 ) and 1,3-O-alkylation (R 2 ) substitution on the calixarene strongly influenced catalyst activity and chiral induction. Optimum results were obtained when R 1 was -C(CH 3 ) 3 and R 2 was -CH 2 CH 2 CH 3 (3b). Under optimized conditions, 3b hydrogenated 1a and 1b in 98 and 96% ee, respectively. Overall, better catalyst performance was observed for "locked" cone-conformers of 3, with higher activity evident for the less sterically hindered 1a (TOF up to 1300 h -1 at P(H 2 ) = 5 atm).