Zn(OTf)2-catalyzed reactions of ethenetricarboxylates with 2-aminobenzaldehydes leading to tetrahydroquinoline derivatives.

Quinolines are an important class of compounds, and the development of new efficient synthetic strategies for the construction of quinolines is of considerable interest. Zinc triflate catalyzed cyclization of ethenetricarboxylate derivatives with 2-aminobenzaldehydes has been examined. The reaction of ethenetricarboxylate with 2-aminobenzaldehydes in the presence of zinc triflate (0.2 equiv) at 80 degrees C in ClCH(2)CH(2)Cl gave bridged tetrahydroquinoline derivatives in 15-95% yield. On the other hand, the reaction at room temperature in CH(2)Cl(2) gave hydroxy tetrahydroquinoline derivatives in 38-90% yield. Heating the hydroxy tetrahydroquinolines with zinc triflate (0.2 equiv) at 80 degrees C in ClCH(2)CH(2)Cl led to the bridged tetrahydroquinoline derivatives in 75-96% yield. Thermal reaction of the bridged tetrahydroquinolines (180 degrees C) gave indole derivatives regioselectively.