Iodine-Promoted N–H/α,β-C(sp3)-Trifunctionalization of <scp>l</scp>-Proline: Access to 3,4-Dihydrobenzo[b][1,7]naphthyridines via Consecutive Decarboxylation/Ring Opening/Dicyclization

A N–H/α,β-C(sp3)-trifunctionalization of l-proline, proceeding through an iodine-promoted consecutive decarboxylation/ring-opening/dicyclization process, is achieved. This strategy affords structurally diverse fused N-heterocycles in good yields with a wide substrate scope. Preliminary mechanistic studies indicate that catabolism of l-proline might be involved in this cascade reaction and the in situ generated intermediate 4-aminobutanal was identified as the key intermediate. Notably, this domino strategy enriches the reactivity of versatile l-proline in the synthesis of fused heterocycles.