Lanthanide Silylamide-Catalyzed Synthesis of Pyrano[2,3-b]indol-2-ones.

A lanthanide silylamide-catalyzed tandem reaction of isatins, diethyl phosphite, and 2,3-diarylcyclopropenones has been developed. A series of pyrano[2,3-b]indol-2-ones were synthesized in high yields. The cooperation of the Lewis acidity of the lanthanide center and the Bronsted basicity of the N(SiMe3)2 anion may be the key factor affecting the catalytic activity of lanthanide amides.