Dioxygen is an abundant,
selective, and sustainable oxidant that is considered ideal for organic
transformations. Oxidative processes using dioxygen as the electron acceptor
without oxygen atom incorporation into the substrate are often referred to as
oxidase reactions. However, the ground state triplet nature of dioxygen makes
such a synthetically valuable pathway incompatible with simple free alkyl
radicals, a ubiquitous class of reactive intermediates in the daily synthesis
of pharmaceuticals, agrochemicals, and complex natural products. Here we report
that a combination of strong cage effect and bimetallic radical-polar crossover
successfully addresses this problem, and opens up an oxidase pathway in cobalt
hydride catalysis. This leads to a general and chemoselective method that
tackles several key challenges in catalytic hydroamination, a fundamental
transformation for amine synthesis. Under balloon pressure of dioxygen at ambient temperature, we demonstrate single-step intra- and
intermolecular formal addition of a variety of nitrogen nucleophiles, including
free amines, sulfonamides, amides, and carbamates, to unactivated alkenes in
the presence of a silane, under solvent-free conditions. Important medicinal
chemistry building blocks such as a-branched tertiary amines can be easily
accessed, which are often difficult targets otherwise due to their steric
hindrance and reducing nature. Mechanistic studies including stoichiometric
experiments with well-defined organocobalt complexes provide support for the
key hypothesis, which points the way to the development of sustainable
processes involving other nucleophiles based on the same design elements.
Propane to olefins tandem catalysis: a selective route towards light olefins production
