Iridium-Catalyzed, Intermolecular Hydroamination of Unactivated Alkenes with Indoles

The addition of an N–H bond
to an olefin is the most direct
route for the synthesis of alkylamines. Currently, intermolecular
hydroamination is limited to reactions of a narrow range of reagents
containing N–H bonds or activated alkenes, and all the examples
of additions to unactivated alkenes require large excesses of alkene.
We report intermolecular hydroamination reactions of indoles with
unactivated olefins. The reactions occur with as few as 1.5 equiv
of olefin to form N-alkylindoles exclusively and
in good yield. Characterizations of the catalyst resting state, kinetic
data, labeling studies, and computational data imply that the addition
occurs by olefin insertion into the Ir–N bond of an N-indolyl complex and that this insertion reaction is faster
than insertion of olefin into the Ir–C bond of the isomeric
C-2-indolyl complex.