124686-29-9Relevant academic research and scientific papers
Biocatalytic access to nonracemic γ-oxo esters: Via stereoselective reduction using ene-reductases
Turrini, Nikolaus G.,Cioc, Rǎzvan C.,Van Der Niet, Daan J. H.,Ruijter, Eelco,Orru, Romano V. A.,Hall, Mélanie,Faber, Kurt
, p. 511 - 518 (2017/08/14)
The asymmetric bioreduction of α,β-unsaturated γ-keto esters using ene-reductases from the Old Yellow Enzyme family proceeds with excellent stereoselectivity and high conversion levels, covering a broad range of acyclic and cyclic derivatives. Various strategies were employed to provide access to both enantiomers, which are versatile precursors of bioactive molecules. The regioselectivity of hydride addition on di-activated alkenes was elucidated by isotopic labeling experiments and showed strong preference for the keto moiety as activating/binding group as opposed to the ester. Finally, chemoenzymatic synthesis of (R)-2-(2-oxocyclohexyl)acetic acid was achieved in high ee on a preparative scale combining enzymatic reduction followed by ester hydrogenolysis.
Mechanistic aspects of the alternating copolymerization of propene with carbon monoxide catalyzed by Pd(II) complexes of unsymmetrical phosphine - Phosphite ligands
Nozaki, Kyoko,Sato, Naomasa,Tonomura, Yoichi,Yasutomi, Masako,Takaya, Hidemasa,Hiyama, Tamejiro,Matsubara, Toshiaki,Koga, Nobuaki
, p. 12779 - 12795 (2007/10/03)
The reaction steps responsible for the highly enantioselective asymmetric copolymerization of propene with carbon monoxide catalyzed by a cationic Pd(II) complex bearing an unsymmetrical chiral bidentate phosphine- phosphite, (R,S)-BINAPHOS [(R,S)-2-(diphenylphosphino)-1,1'-binaphthalen-2'- yl 1,1'-binaphthalene-2,2'-diyl phosphite = L1], have been studied. Stepwise identification and characterization were carded out for catalyst precursors (SP-4-2)- and (SP-4-3)-Pd(CH3)Cl(L1) (1a and 1b) and (SP-4-3)- [Pd(CH3)(CH3CN)(L1)]·X1 (X1 = B{3,5-(CF3)2C6H3}4) (2), and complexes related to the reaction steps, (SP-4-3)- [Pd(COCH3)(CH3CN)(L1)]·X1 (3), (SP-4-3)- and (SP-4-4)- [Pd{CH2CH(CH3)COCH3}(L1)]·X1 (4a and 4b), (SP-4-3)- [Pd{COCH2CH(CH3)COCH3}(CH3CN)(L1)]·X1 (5), and (SP-4-3)- [Pd{CH2CH(CH3)COCH2CH(CH3)COCH3}(L1]·X1 (6). An X-ray structure of alkyl complex 4a has been obtained. Studies on [Pt(CH3)2(L1)] (8) reveal that the methyl group is more stabilized at a position trans to the phosphine than at the cis position. This is consistent with the structures of 1-6 in which all carbon substituents are trans to the phosphine moiety in their major forms. On the basis of analogous studies using platinum complexes, an isomerization from (SP-4-3)-[Pd(CH3)(CO)(L1)]·X1 (13a) to the (SP-4-4) isomer (13b) is suggested to occur for the CO-insertion process 2 → 3, which results in the activation of the methyl group for the migration to the coordinated CO. Rapid equilibrium was observed between the two isomers 4a and 4b during the CO insertion process to give 5. Theoretical studies have been carded out on the transformation of 3 to 4a and 4b. The B3LYP and MPn calculations indicated that the alkene insertion into the Pd-acyl bond trans to a phosphine is more favorable than that into the Pd-acyl bond trans to a phosphite. The MM3 calculations demonstrated that one specific transition structure is more favorable than the other possible transition structures for the transformation of (SP-4-4)-[Pd(COCH3)(propene)(L1)]·X1 (14b) to 4b. The difference originates from the steric effects of the BINAPHOS ligand, and the results account for high enantio- and regioselectivities experimentally observed. The two key steps, propene insertion into 3 and CO insertion into 4, were monitored by 1H NMR spectroscopy. The activation energies for these two steps were estimated to be 19.0-19.6 kcal/mol at -20 to 0 °C, their difference being insignificant. The living nature of the copolymerization was proved. Some related chiral ligands were examined for the copolymerization. Copolymerization of other olefins with CO was also investigated.
