Modular synthesis of a new class of bis(amino-oxazoline) using palladium-catalyzed Buchwald-Hartwig amination methodology

Academic Article

Abstract

  • The palladium-catalyzed Buchwald-Hartwig aryl amination between 2,2′- diaminobiphenyl and 2 equiv of 2-(2′-bromophenyl)oxazoline has been used to prepare a new class of tetradentate bis(amino-oxazoline). The reaction between 2,2′- diaminobiphenyl and 1 equiv of 2-(2′-bromophenyl) oxazoline is highly selective for monoarylation, and the resulting products have been reacted in a second arylation to afford unsymmetrically substituted bis(amino-oxazolines). These new diamido/donors belong to the tropos class of ligand and exist as an equilibrium mixture of S,aS,S- and S,aR,S- diastereoisomers, which interconvert by rotation about the biaryl axis. Variable-temperature 1 H NMR studies and line-shape analysis of simulated spectra gave ΔH ‡ and ΔS ‡ values of 51.5-57 kJ mol -1 and -25.9 to -57.0 J mol -1 K -1 , respectively, for diastereointerconversion. Interestingly, reaction of one of the symmetrical bis(amino-oxazoline) with [Cu(MeCN) 4 ][PF 6 ] results in dynamic resolution to afford diastereopure (S,aS,S)-[Cu(L)][PF 6 ], which has a highly unusual sawhorse geometry at copper with the two oxazolines occupying trans coordination sites and two weak interactions to the nitrogen atoms of the secondary amino groups. 1 H and 13 C NMR spectra of this copper complex are entirely consistent with a single C 2 - symmetric diastereoisomer in solution that shows no sign of diastereointerconversion even after standing for one week. © 2006 American Chemical Society.
  • Authors

    Published In

  • Organometallics  Journal
  • Digital Object Identifier (doi)

    Author List

  • Doherty S; Knight JG; Smyth CH; Sore NT; Rath RK; McFarlane W; Harrington RW; Clegg W
  • Start Page

  • 4341
  • End Page

  • 4350
  • Volume

  • 25
  • Issue

  • 18