One-Pot Synthesis of Imidazo[2,1-a]phthal-azines

Significance

The facile and general synthesis of imidazo[2,1-a]phthalazines 3 is reported. The reaction involves the Pd- and Cu-mediated coupling of 1-aminoimidazoles 1 and 2-bromobenzaldehydes 2 with preceding or concurrent imine formation. Both electron-rich and electron-poor aryl aldehydes are equally tolerated, as are a variety of substituents in the 1-aminoimidazole fragment. One example of a pyridine-3-carboxaldehyde was also demonstrated, albeit in slightly decreased yield (27%). Quantitative conversion into imine 4a was observed by carrying out the reaction in the presence of either (but not both) of the metals, suggesting that imine formation occurs before or concurrently with imidazole arylation.