Annuloselectivity of Dibenzoxazepines and Arynes in the Presence of CO2: [2+2] vs [2+2+2] Annulation

Abstract The annulation of arynes with dibenzo[ b , f ][1,4]oxazepines ( N ‐aryl cyclic imines) in the presence of CO 2 has been studied in comparison with 3,4‐dihydroisoquinolines ( N ‐alkyl cyclic imines). For the reaction with dibenzo[ b , f ][1,4]oxazepines, [2+2] annulation takes place specifically with arynes, with CO 2 acting only as the protecting gas. 3,4‐dihydroisoquinolines, however, exclusively underwent [2+2+2] annulation with arynes and CO 2 , with CO 2 as a reactant. Our findings offer insights into imine‐aryne annulation under CO 2 and suggest that steric and nucleophilic factors control the annuloselectivity. Reactivity analysis revealed that electron‐rich and less steric N ‐alkyl cyclic imines and electron‐deficient benzynes favor the [2+2+2] annulation, while electron‐deficient and bulky N ‐aryl cyclic imines prefer the [2+2] annulation. In the [2+2] annulation, the Hammett analyses reveal that both the nucleophilic attack of imines to benzynes (the first step, negative ρ ) and the attack of phenyl anions on the iminium species (the second step, positive ρ ) affect the reaction rate.