Solvent/Base Effects in the Selective Domino Synthesis of Phenanthridinones That Involves High‐Valent Palladium Species: Experimental and Theoretical Studies

The domino reaction of o ‐bromobenzamides 1 a – m in the presence of K 2 CO 3 and the [PdCl 2 (PPh 3 ) 2 ] catalyst granted a selective access to phenanthridinones 2 or to the new 1‐carboxamide phenanthridinones 3 depending on the solvent, DMF or 1,4‐dioxane, respectively. Investigations of the reaction parameters provided the first example of a direct correlation between the base dissociation and the solvent polarity on the selectivity observed. Moreover, mechanistic studies (NMR spectroscopy and ESI‐MS monitoring) allowed us to characterize Pd II palladacycle 4 and biaryl species as common intermediates for these two domino processes. On that basis, C(sp 2 )C(sp 2 ) bond formation is envisaged by generation of a Pd IV complex after oxidative addition of 1 into Pd II palladacycle 4 , a rationale that is supported by DFT calculations. A general catalytic cycle is proposed to account for these observations.