2-(Methoxycarbonyl)ethyl as a Removable N-ProtectingGroup: Synthesis of Indoloisoquinolinones by Pd(II)-Catalyzed IntramolecularDiamination of Alkynes.

Pd(II)-catalyzeddouble cyclization of 1,2-diarylethynes bearingan N-methyl-N-[2-(methoxycarbonyl)ethyl]aminoand an aminocarbonyl group at the orthopositionsof the two aromatic rings afforded the tetracyclic N-[2-(methoxycarbonyl)ethyl]indoloisoquinolinones in good to excellentyields. The N-[2-(methoxycarbonyl)ethyl] group isreadily removed under basic conditions (DBU, DMF, 120 °C) toafford the corresponding tetracycles with a free indolyl nitrogenin excellent yields. The 2-(methoxycarbonyl)ethyl as a removable N-protecting group is illustrated in other Pd(II)- and Pd(0)-catalyzedand selenium-mediated transformations. [ABSTRACT FROM AUTHOR]