O-arylation versus C-arylation: copper-catalyzed intramolecular coupling of aryl bromides with 1,3-dicarbonyls.

The copper-catalyzed intramolecular coupling of aryl bromides with 1,3-dicarbonyls via a six-membered ring closure was examined. With CuI (10 mol %) as the catalyst, N,N'-dimethylethylenediamine as the ligand, and Cs2CO3 as the base, the reactions of alpha-(2-bromobenzyl)-beta-keto esters in THF at refluxing temperature afforded the corresponding substituted 4H-1-benzopyrans in high yields via O-arylation. On the other hand, the reactions of delta-(2-bromophenyl)-beta-keto esters in refluxing dioxane led to the formation of 3,4-dihydronaphthalen-2(1H)-one derivatives via C-arylation.