Hydroxylamines As Bifunctional Single-Nitrogen Sources for the Rapid Assembly of Diverse Tricyclic Indole Scaffolds

Conventional approaches on using
hydroxylamine derivatives as single
nitrogen sources, for the construction of n-membered
(n > 3) N-heterocycles, rely upon two chemical
operations
by involving sequential nucleophilic and electrophilic C–N
bond formations. Here, we report a highly efficient cascade of alkyne
insertion/C–H activation/amination for the rapid preparation
of a myriad of tricyclic indoles, in a single-step transformation,
by using bifunctional secondary hydroxylamines. It is noteworthy that
judicious selection of applicable amino agents, for enabling the prior
oxidative addition of aryl iodide to initial Pd(0) species and subsequent
two C–N bonds formation, was the key to the success of this
reaction. Control experiments indicated that a five-membered palladacyclic
intermediate played a crucial role in promoting the final aminative
ring closure.