Synthesis of bicyclic imidazoles via [2 + 3] cycloaddition between nitriles and regioselectively generated α-imino gold carbene intermediates.
The cyclic α-imino gold carbene intermediate B is most likely generated in situ via regioselective nitrene transfer from an azido group to a tethered terminal alkyne in the presence of a gold catalyst and at ambient temperature. This highly electrophilic intermediate can react with a weakly nucleophilic nitrile, which is used as the reaction solvent, to deliver a bicyclic imidazole rapidly in an overall bimolecular [2 + 2 + 1] cycloaddition and in mostly serviceable yield. The competing intramolecular Huisgen reaction, although likely also catalyzed by gold, is minimized by using AuCl(3) as the catalyst.
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA.
Yuanjing
Y
Xiao
Liming
L
Zhang
D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D061565:Cycloaddition Reaction; D017612:Gold Compounds / Q000737:chemistry*; D006574:Heterocyclic Compounds, 2-Ring / Q000138:chemical synthesis*; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry*; D013237:Stereoisomerism
D000480:Alkynes; D017612:Gold Compounds; D006574:Heterocyclic Compounds, 2-Ring; D007093:Imidazoles; D009570:Nitriles; C038016:gold chloride; C030011:carbene; D008697:Methane