Dehydrative Transformation of Spirooxindoles to Pyrido[2,3-<i>b</i>]indoles via POCl₃

Abstract

A two-step one-pot efficient synthesis of pyrido[2,3-<i>b</i>]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.