A Mild Ethynylating Reagent

1-[(Triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (=TIPS-EBX) is a mild ethynylating reagent and well used for site-selective ethynylations. For example, a palladium catalyzed ethynylation of indoles proceeds at C2-selectively, while complementary C3-selective ethynylation is accomplished by using gold chloride as a catalyst. Gold catalyst-promoted site-selective ethynylations are applied to thiophenes and N,N-dialkyl anilines affording C2-ethynylated thiophenes and para-ethynylated anilines. A TIPS group on the alkynes can be easily removed under basic conditions and affords related terminal alkynes. Thus, TIPS-EBX is an efficient ethynylating reagent applicable for click chemistry and material sciences.