Tempering the Reactivities of Postulated α-Oxo Gold Carbenes Using Bidentate Ligands: Implication of Tricoordinated Gold Intermediates and the Development of an Expedient Bimolecular Assembly of 2,4-Disubstituted Oxazoles

• DOI: 10.1021/ja307948m
• Publication Date: 2012-10-05T18:49:58Z
• Authors: Yingdong Luo; Kegong Ji; Yuxue Li; Liming Zhang
• Keywords: Oxazole; Hydroamination; Alkyne; Annulation

2,4-Oxazole is an important structural motif in various natural products. An efficient modular synthesis of this structure has been achieved via a [3 + 2] annulation between terminal alkyne and carboxamide using gold-catalyzed oxidation strategy. The postulated reactive intermediate, α-oxo gold carbene, previously known to be highly electrophilic hence unlikely trapped by stoichiometric external nucleophiles, coerced react smoothly with the en route oxazole ring P,N- or P,S-bidentate ligand such as Mor-DalPhos; stark contrast, often-used ligands monodentate phosphines N-heterocyclic carbenes are totally ineffective. role these bidentate reaction attributed formation tricoordinated carbene which less more chemoselective when reacting nucleophiles. success phosphine temper reactivities situ-generated likely open many new opportunities apply oxidative catalysis development novel methods, implication intermediates homogeneous should stimulate further advances catalysis.