C2-Selective Direct Alkynylation of Indoles

The first C2-selective alkynylation of indoles using the hypervalent iodine reagent triisopropylsilylethyny1-1,2-benziodoxol-3(1H)-one (TIPS-EBX) with Pd(II) as a catalyst is described. This convenient and robust method gives a single-step access to substituted alkynyl indoles with very high C2 selectivity. The reaction is orthogonal to classical Pd(0) cross-coupling reactions, as it is tolerant to bromide and iodide substituents. The used silyl protecting group can be easily removed to give terminal acetylenes.