Ugi-post functionalization, from a single set of ugi-adducts to two distinct heterocycles by microwave-assisted palladium-catalyzed cyclizations: tuning the reaction pathways by ligand switch.
Linear amides 4, prepared in one step by the Ugi four-component reaction, were converted to 3,4-dihydroquinoxalin-3-ones (5) or to 2-(2-oxoindolin-1-yl)acetamides (6) dependent on the catalytic conditions. While microwave irradiation was found to be determinant on the reaction efficiency, the choice of ligand diverged the reaction pathways. Heating a solution of 4 in dioxane/MeCN (v/v = 85/15) under microwave irradiation conditions in the presence of Pd(dba)(2) (0.05 equiv) and Cs(2)CO(3) (2 equiv), using XPhos as a supporting ligand, afforded the 3,4-dihydroquinoxalin-3-ones (5) via an intramolecular N-arylation of the secondary amide. On the other hand, using BINAP as ligand under otherwise identical conditions, intramolecular alpha-CH arylation of tertiary amide occurred to furnish the oxindoles (6).
Erb
William
W
Institut de Chimie des Substances Naturelles, CNRS, 91198 Gif-sur-Yvette Cedex, France.
Neuville
Luc
L
Zhu
Jieping
J
D002384:Catalysis; D003500:Cyclization; D004146:Dioxanes / Q000737:chemistry; D007211:Indoles / Q000737:chemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008872:Microwaves; D015394:Molecular Structure; D000078183:Oxindoles; D010165:Palladium / Q000737:chemistry*; D011810:Quinoxalines / Q000138:chemical synthesis / Q000737:chemistry; D012997:Solvents; D013329:Structure-Activity Relationship
D004146:Dioxanes; D007211:Indoles; D008024:Ligands; D000078183:Oxindoles; D011810:Quinoxalines; D012997:Solvents; C022960:2-oxindole; D010165:Palladium