Molecules
displaying an α-trialkyl-α-tertiary amine
motif provide access to an important and versatile area of biologically
relevant chemical space but are challenging to access through existing
synthetic methods. Here, we report an operationally straightforward,
multicomponent protocol for the synthesis of a range of functionally
and structurally diverse α-trialkyl-α-tertiary amines,
which makes use of three readily available components: dialkyl ketones,
benzylamines, and alkenes. The strategy relies on the of use visible-light-mediated
photocatalysis with readily available Ir(III) complexes to bring about
single-electron reduction of an all-alkyl ketimine species to an α-amino
radical intermediate; the α-amino radical undergoes Giese-type
addition with a variety of alkenes to forge the α-trialkyl-α-tertiary
amine center. The mechanism of this process is believed to proceed
through an overall redox neutral pathway that involves photocatalytic
redox-relay of the imine, generated from the starting amine-ketone
condensation, through to an imine-derived product. This is possible
because the presence of a benzylic amine component in the intermediate
scaffold drives a 1,5-hydrogen atom transfer step after the Giese
addition to form a stable benzylic α-amino radical, which is
able to close the photocatalytic cycle. These studies detail the evolution
of the reaction platform, an extensive investigation of the substrate
scope, and preliminary investigation of some of the mechanistic features
of this distinct photocatalytic process. We believe this transformation
will provide convenient access to previously unexplored α-trialkyl-α-tertiary
amine scaffolds that should be of considerable interest to practitioners
of synthetic and medicinal chemistry in academic and industrial institutions.