Rh(I)/Bisoxazolinephosphine-Catalyzed Regio- and Enantioselective Allylic Substitutions
作者:Wen-Bin Xu、Samir Ghorai、Wenyu Huang、Changkun Li
DOI:10.1021/acscatal.0c00712
日期:2020.4.17
Rhodium(I)/bisoxazolinephosphine combination has been developed as a general catalyst to achieve the dynamic kinetic asymmetric allylation of a variety of nitrogen, carbon, oxygen, and sulfur pronucleophiles from branched racemic allylic carbonates. Exclusive branch-selectivity and up to 99% enantiomeric excess could be obtained under neutral conditions. Linear allylic substrates (both Z and E) could
Rhodium-Catalyzed Regio- and Enantioselective Direct Allylation of Methyl Ketones
作者:Changkun Li、Bing Li
DOI:10.1055/a-1892-4134
日期:2022.11
We report a highly branch-selective and enantioselective allylic alkylation of simple ketones with racemic aliphatic allylic carbonates under mild conditions. By using a Rh–bisoxazolinephosphine system and catalytic amounts of a base in THF, a series of chiral β-branched γ,δ-unsaturated ketones were obtained with excellent regio- and enantioselectivities. An outer-sphere nucleophilic substitution C–C
New chiral NPN-type tridentate ligands containing two oxazoline rings and one phosphine have been synthesized, and their Ru(II) complexes show high reactivity and enantioselectivity in transfer hydrogenations of both aryl alkyl and dialkyl ketones (with ee's up to 92% for a dialkyl ketone). Copyright (C) 1996 Elsevier Science Ltd
Construction of P-stereogenic center by selective ligation of NPN type ligands and application to asymmetric allylic substitution reactions
Chiral bisoxazolylphosphine ligands 1 [(S,S)-PhP(Ox-R)(2): R = Me, Pr-i, Bu-t] with an N-P-N backbone were prepared from chiral 4-alkyl-2-phenyl-4,5-dihydrooxazole compounds. These ligands coordinated to Pd(II) ion as bidentate ligands selectively to give a stereogenic phosphorus atom. The Pd-(S,S)-PhP(Ox-Bu-t)(2) 1c catalyst evoked high enantioselectivity in asymmetric allylic substitutions of acyclic substrates using dimethyl sodiomalonate as nucleophile. In the reaction of 3-penten-2-yl acetate, which affords a pi-allyl intermediate with a small steric factor, the Pd-1c catalyst successfully induced very high enantioselectivity (94% ee) indicating the effectiveness of the P-stereogenic center formed by selective ligation of ligand 1. In the reaction of cyclic substrates, moderate to high enantioselectivity was obtained by Pd-1 catalyst using the sodium salt of dimethyl methylmalonate. (C) 2003 Elsevier Ltd. All rights reserved.