1,3‐Dipolar Cycloadditions of Cyanoheteroarenes with non‐stabilized Azomethine Ylides : C≡N vs Aromatic C=C Reactivity

Indoles, benzofurans and benzothiophenes substituted by a cyano group at positions 2 or 3 are shown to behave differently toward azomethine ylide 1,3‐dipole 1, in (3+2) cycloadditions. While the C2=C3 aromatic double bond of 3‐cyanoheteroarene reacts as dipolarophile to generate the corresponding dearomatized cycloadducts, the C≡N bond of 2‐cyanobenzofuran reveals more reactive and imidazoline are obtained in this case. 2‐Cyanoindole substituted by an electron‐withdrawing triflyl group on the nitrogen atom allows the formation of the bis‐cycloadduct where the C=C and C≡N moieties both reacted. The C≡N vs C=C reactivity is nicely supported by DFT computations. (3+2) Cycloadditions involving cyanoheteroarenes and an electron‐rich non‐stabilized azomethine ylide are studied according to the nature of arene and position of the cyano group. A chemoselective reaction occurs on the C2=C3 aromatic double bond, on the C≡N bond or on both. The C≡N vs C=C reactivity is nicely supported by DFT computations.