Construction of P-stereogenic center by selective ligation of NPN type ligands and application to asymmetric allylic substitution reactions
作者:Takamichi Yamagishi、Masatoshi Ohnuki、Takahiro Kiyooka、Dai Masui、Kiyoshi Sato、Motowo Yamaguchi
DOI:10.1016/j.tetasy.2003.09.004
日期:2003.10
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.