Metal-Free and Regioselective Synthesis of Functionalized α‑Carbolines via [3 + 3] Annulation of Morita–Baylis–Hillman Acetates of Nitroalkenes with Iminoindolines

A facile, metal-free method for the synthesis of substituted α-carbolines from secondary Morita–Baylis–Hillman (MBH) acetates of nitroalkenes is presented. The cascade reaction of MBH acetates with tosyliminoindolines occurs regioselectively to form various α-carbolines with a wide substrate scope. The reaction involves mild conditions, and the products are formed in high yields within a short reaction time. The amenability of the reaction to scale up and synthetic applications of the products have been demonstrated.