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, prepd. in one step by the Ugi four-component reaction, were converted to 3,4-dihydroquinoxalin-3-ones or to 2-(2-oxoindolin-1-yl)acetamides dependent on the catalytic conditions. While microwave irradn. was found to be determinant on the reaction efficiency, the choice of ligand diverged the reaction pathways. Heating a soln. of the linear amides in dioxane/MeCN (vol./vol. = 85/15) under microwave irradn. conditions in the presence of Pd(dba)2 (0.05 equiv) and Cs2CO3 (2 equiv), using XPhos as a supporting ligand, afforded the 3,4-dihydroquinoxalin-3-ones via an intramol. N-arylation of the secondary amide. On the other hand, using BINAP as ligand under otherwise identical conditions, intramol. alpha -CH arylation of tertiary amide occurred to furnish the oxindoles. [on SciFinder (R)]