Unsymmetrical terdentate phosphorus-nitrogen-nitrogen (PNN) ligands: effect of the M/L ratio and the pendant group on stereoselectivity
摘要:
Twelve novel, unsymmetrical terdentate pyrrolidine-based phosphorus-nitrogen ligands were prepared. These ligands promoted very high catalytic activity in the palladium-catalysed allylic substitution reactions of 1,3-diphenylpropenyl acetate with malonate esters (100% conversion at 0degreesC in <2 h). Enantioselectivities up to 94% were attained. An unusual effect of metal-to-ligand ratio was observed. Various structural features affecting the enantioselectivity and stereoinduction were examined and discussed. (C) 2003 Elsevier Ltd. All rights reserved.
contains a hard donor site in addition to the soft donor in a molecule. Phosphorus atom strongly bonds to rhodium(I), and the amide carbonyl oxygen is coordinatively labile. The reaction efficacy of phenylboronic acid with cyclopent-2-en-1-one was significantly dependent on the possibility of coordination of the amide carbonyl oxygen to rhodium(I).
Proline-Based P,O Ligand/Iridium Complexes as Highly Selective Catalysts: Asymmetric Hydrogenation of Trisubstituted Alkenes
作者:Denise Rageot、David H. Woodmansee、Benoît Pugin、Andreas Pfaltz
DOI:10.1002/anie.201104105
日期:2011.10.4
O joins the mix: P,O ligands (L1) form efficient iridiumcatalysts for the asymmetric hydrogenation of olefins. The proline‐derived ligands lead to high enantioselectivities with several classes of alkenes, most notably with α,β‐unsaturated carboxylic esters and ketones, where they match or even surpass the ee values reported for the best N,P and C,N ligands.
An Efficient Procedure for the Preparation of (<i>E</i>)-α-Alkylidenecycloalkanones Mediated by a CeCl<sub>3</sub>·7H<sub>2</sub>O−NaI System. Novel Methodology for the Synthesis of (<i>S</i>)-(−)-Pulegone<sup>1</sup>
synthons used as the key intermediates in many important syntheses. Because of their potential, a general method of preparation from readily available starting materials, under very mild conditions, was considered to be worthwhile. Cerium(III) chlorideheptahydrate in combination with sodiumiodide in refluxing acetonitrile promotes a regio- and stereoselective beta-elimination reaction to (E)-2-alky
Solvent effect and NMR behaviour in a chiral amidophosphine mediated reaction of organocuprate with chalcone
作者:Motomu Kanai、Kenji Koga、Kiyoshi Tomioka
DOI:10.1039/c39930001248
日期:——
A dramatic reversal in the direction of enantiofacial differentiation has been observed in a chiral phosphine mediated reaction of organocuprate with chalcone providing S- and R-products in diethyl ether and tetrahydrofuran (THF), respectively, and correlated with the pattern of coordination.