Efficient [4+1]/[3+2+1] bis-cyclizations stereoselectively yielding unprecedented polyacyclic indeno-fused xanthenes

Concise and efficient 4+1]/3+2+1] bis-cyclizations of o-phthalaldehyde with cyclic 1,3-dicarbonyls have been established for the stereoselective synthesis of unprecedented polycyclic indeno2,1-l]xanthene derivatives. The multicomponent domino reaction (MDR, AB₂ type) is easy to perform by mixing inexpensive substrates in HOAc at room temperature. The present synthesis shows attractive properties such as the simple one-pot fashion, high bond-forming efficiency, and easy purifications. Up to two new rings and four sigma-bonds were achieved in these MDRs without using any metal catalysts.