[Cp∗IrCl2]2-catalysed cyclization of 2-alkynylanilines into indoles

Preparation of symmetrical C2-C2-linked bis- and tris-6-bromoindoles by Sonogashira couplings and 5-endo-dig cyclization induced by nBu4NF

“…The 5-endo-dig cyclization of ortho-alkynylaniline derivatives can be conducted by bases, [16][17][18][19][20][21][22] metals [23][24][25][26][27][28] and in the presence of electrophiles that can add functional groups to the indole nucleus. [29][30][31][32][33][34][35][36] In order to keep the procedure simple, the protocol using tetrabutylammonium fluoride (TBAF) 17,18 was chosen.…”

2‐(Alkynyl)anilines and Derivatives — Versatile Reagents for Heterocyclic Synthesis

“…The next wide set of conditions towards indole synthesis relies on the use of Lewis acids [17–59] . The activation of a triple bond to nucleophilic addition is followed by the 5‐ endo ‐dig pathway with subsequent proton migration from the nitrogen atom to position 3, as shown in the Scheme 4.…”

“…Straightforward cyclizations of 2‐alkynylanilines in the presence of In, [18,19] Zn, [20–22] Hg [23–25] salts, as well as Cu, [26–28,37] Ag, [29,30] Pt, [31,32] Au, [33–36] or Pd [40–44] are well‐documented. Coordination complexes could also be considered acting as Lewis‐acids towards indole synthesis, [39–50] although it should be noted that the mechanism of action for Pd and Pt complexes differs. In contrast, for Ru‐catalyzed cyclizations there are only fragmentary publications [57] .…”

“…In contrast, for Ru‐catalyzed cyclizations there are only fragmentary publications [57] . As a rule, coordinated Ag, [45] Ir, [49,50] Au [52–55,58] species can promote the cyclization at r.t. and with low 0.25–1 mol% catalyst loadings. Gold‐catalyzed cyclizations of the sort were reviewed by Arcadi et al [59] .…”

Recent advances in the synthesis of indoles from alkynes and nitrogen sources

“…The synthesis of 2-substituted indoles 94 via [Cp*IrCl 2 ] 2 -cata-lysed cyclization of internal ortho-alkynylanilines has been developed (Scheme 83). 112 If hydrogen-substituted alkynes were used as substrates, 2,2′-biindoles 96 were obtained in good yields (Scheme 84). 113 The mechanistic studies indicated that the reaction proceeds via formation of a (vinylidene) iridium intermediate 95 and an intramolecular hydroamination, followed by the insertion reaction.…”