Sulfonamide and Tertiary Amine as Nucleophiles in Pd(II)-Catalyzed Diamination of Alkynes: Synthesis of Tetracyclic Indolobenzothiazine S,S‑Dioxides

Pd(II)-catalyzed oxidative double cyclization of the 1,2-diarylethynes bearing an N-methyl-N-(2-methoxycarbonyl)ethylamino and an aminosulfonyl group afforded indolobenzothiazine S,S-dioxides in good to excellent yields. The 2-(methoxycarbonyl)ethyl group attached to the indolyl nitrogen is readily removed under basic conditions (DBU, DMF, 120 °C) to provide the corresponding tetracycles with a free indolyl nitrogen in excellent yields.