Dehydrative Transformation of Spirooxindoles to Pyrido[2,3‑b]indoles via POCl₃

A two-step one-pot efficient synthesis of pyrido­[2,3-b]­indoles via reaction between isatin, α-amino acid, and dipolarophile has been developed. The initial 1,3-dipolar cycloaddition between the reactants that is performed in the presence of either CuI or methanol results in spirooxindoles that undergo POCl₃-mediated intramolecular dehydrative transformation to afford the title compounds.