A photochemical dehydrogenative strategy for aniline synthesis

A dual cobalt and photocatalysis system provides a way to assemble anilines from cyclohexanones and amines by progressively dehydrating the intermediate imine. Chemical reactions that reliably join two molecular fragments together (cross-couplings) are essential to the discovery and manufacture of pharmaceuticals and agrochemicals(1,2). The introduction of amines onto functionalized aromatics at specific and pre-determined positions (orthoversusmetaversuspara) is currently achievable only in transition-metal-catalysed processes and requires halogen- or boron-containing substrates(3-6). The introduction of these groups around the aromatic unit is dictated by the intrinsic reactivity profile of the method (electrophilic halogenation or C-H borylation) so selective targeting of all positions is often not possible. Here we report a non-canonical cross-coupling approach for the construction of anilines, exploiting saturated cyclohexanones as aryl electrophile surrogates. Condensation between amines and carbonyls, a process that frequently occurs in nature and is often used by (bio-)organic chemists(7), enables a predetermined and site-selective carbon-nitrogen (C-N) bond formation, while a photoredox- and cobalt-based catalytic system progressively desaturates the cyclohexene ring en route to the aniline. Given that functionalized cyclohexanones are readily accessible with complete regiocontrol using the well established carbonyl reactivity, this approach bypasses some of the frequent selectivity issues of aromatic chemistry. We demonstrate the utility of this C-N coupling protocol by preparing commercial medicines and by the late-stage amination-aromatization of natural products, steroids and terpene feedstocks.