“…In both cases the first reaction step is an intramolecular cyclization, leading to spirocyclic intermediates XVII and XVIII, which further evolve to the final products after 1,2-migration of the vinyl group (Scheme 14). [47] A similar mechanism -involving gold activation of an alkyne, nucleophilic addition of C-3 of indole to form a spirocyclic compound, and vinyl 1,2-migration, prior to rearomatization and protodeauration -was also invoked by Enders [48] and Van Der Eycken, [49,50] among others, [51][52][53] to justify the cyclization of alkynylindoles to afford different polycycles. On the other hand, different research groups have concentrated their attention on the study of alternative mechanistic pathways, including other types of 1,2-migrations of spirocyclic intermediates, starting from indoles bearing alkynes on the C-3 position.…”