NHC-stabilized gold(I) complexes: suitable catalysts for 6-exo-dig heterocyclization of 1-(o-ethynylaryl)ureas.
3-Substituted 1-(o-ethynylaryl)ureas 1 selectively undergo either 6-exo-dig or 5-endo-dig cyclization (to give 4-methylene-3,4-quinazolin-2-ones 2 or indoles 3, respectively) depending on the choice of the metal, ligand, and reaction conditions. The best results (up to 96% yield) in the preparation of the hydroamination products 2 are achieved with the highly bulky NHC-stabilized cationic gold(I) complex [Au(IPr)](+). Conversely, ureas bearing an internal alkyne lead to the 5-endo-dig cyclization mode regardless of the gold(I) complex employed. Whereas the nature of the substituent at N-3 does not have any influence on the regiochemistry observed, it does, in some cases, affect the efficiency of these transformations.
Gimeno
Ana
A
Departamento de Química Orgánica, Universidad de Valencia, 46100 Burjassot, Valencia, Spain.
Medio-Simón
Mercedes
M
de Arellano
Carmen Ramírez
CR
Asensio
Gregorio
G
Cuenca
Ana B
AB