RESUMO
Tricomponent cobalt(salen)-catalyzed carbofunctionalization of unsaturated substrates by radical-polar crossover has the potential to streamline access to broad classes of heteroatom-functionalized synthetic targets, yet the reaction platform has remained elusive, despite the well-developed analogous hydrofunctionalizations mediated by high-valent alkylcobalt intermediates. We report herein the development of a cobalt(salen) catalytic system that enables carbofunctionalization. The reaction entails a tricomponent decarboxylative 1,4-carboamination of dienes and provides a direct route to aromatic allylic amines by obviating preformed allylation reagents and protection of oxidation-sensitive aromatic amines. The catalytic system merges acridine photocatalysis with cobalt(salen)-catalyzed regioselective 1,4-carbofunctionalization that facilitates the crossover of the radical and polar phases of the tricomponent coupling process, revealing critical roles of the reactants, as well as ligand effects and the nature of the formal high-valent alkylcobalt species on the chemo- and regioselectivity.
RESUMO
Spiro[indoline-3,4'-piperidine] is a significant structural scaffold in numerous polycyclic indole alkaloids with a variety of bioactivities. In this study, a synthetic strategy was developed to access spiro[indoline-3,4'-pyridin]-2-yl carbamate via an AgOTf/PPh3-catalyzed tandem cyclization of tryptamine-ynesulfonamides. The unique feature of this strategy is the efficient intermolecular capturing of the in situ generated spiroindoleninium intermediates with carbamates, leading to the diastereoselective syntheses of spiro[indoline-3,4'-pyridin]-2-yl carbamate derivatives. A broad scope of this cyclization was demonstrated by a variety of tryptamine-ynesulfonamide substrates and several carbamates. A plausible mechanism of this reaction was proposed.