Diversity-Oriented, One Step Synthesis of Chromeno[2,3-

A general and efficient synthesis of tetracyclic chromeno[2,3-b]indoles, thiochromeno[2,3-b]indoles and 6H-indolo[2,3-b]quinolines has been achieved through a microwave-assisted, metal free, base catalyzed domino Knoevenagel condensation, intramolecular cyclization process starting from simple indoline-2-thiones and 2-substituted benzaldehyde derivatives. This approach provides a straightforward, atom economical and concise route to access a range of otherwise not easily available heterocycles in good yields.