Dithiocarbamates: new organic catalysts for the photochemical generation of radicals

Identificador:  TDX:4249

Handle: https://hdl.handle.net/20.500.11797/TDX4249

Autors:  Spinnato, Davide

Resum:
En conclusión, se ha demostrado que los aniones ditiocarbamato y xantato son una clase versátil de organocatalizadores útiles para activar una variedad de precursores de radicales y generar intermediarios de capa abierta bajo fotoirradiación con fotones de baja energía. Las estrategias catalíticas desarrolladas pueden enriquecer las herramientas disponibles en química orgánica sintética. In my doctoral studies, I have exploited dithiocarbamate and xanthate anions as organocatalysts for the generation of radicals under photochemical conditions. Interestingly, this new class of catalysts could use distinct and complementary mechanisms to activate different substrates towards radical formation. In particular, the high nucleophilicity of our dithiocarbamate catalyst allowed us to generate open-shell intermediates from readily available alkyl (pseudo)halides through an SN2 pathway. The ensuing radicals have been trapped by silyl enol ethers to deliver á-alkylated ketones. The method's mild reaction conditions and functional group tolerance allowed us to install, at the ketones' á-position, moieties not compatible with classical anionic processes. In addition, the redox neutral conditions of this process made it tolerant of a cinchona-based amine catalyst, which was used to develop an effective protocol for the asymmetric alkylation of cyclic ketones. On the other hand, the high electron-donicity of dithiocarbamate and xanthogenate donors have been exploited to activate redox active radical precursor through a catalytic electron donor acceptor (EDA) complex manifold. The radicals generated via the catalytic EDA approach have been exploited in redox-neutral and net-reductive transformations.