New Strategies for C(sp3)-H Functionalization

Identifier:  TDX:3123

Handle: https://hdl.handle.net/20.500.11797/TDX3123

Authors:  Bafaluy Español, Daniel

Abstract:
This thesis summarize recent novel advances in the field of oxidative aliphatic C-H functionalization. More sustainable methods for C-N and C-F bond construction are herein presented, each one of those overcoming important limitations of the state-of-the-art stablished technologies. First, an electrochemical intramolecular amination approach toward synthesis of pyrrolidines and piperidines was described. In this novel approach, saturated five- and six-membered ring N-heterocycles can be obtained within the same experimental conditions. From an environmental approach, and outstanding sustainability and atom economy is achieved, since molecular hydrogen is formed as the sole by-product. Subsequently, an unprecedented activation of N-F bonds promoting intramolecular aliphatic amination was developed. In this sense, fluorinated amines were employed as effective transferable nitrogen groups for pyrrolidine and piperidine formation in the Hofmann-Löffler reaction context. The two series of products can be prepared with a unified catalytic system based on a well-defined CuI complex. The reaction occurs without the need of additional additives for smooth synthesis of a wide diversity of cyclized products. The mechanism of the reaction was extensively studied by a plethora of experimental physical organic techniques together with theoretical calculations. Finally, we employed our expertise on iodine chemistry and Hofmann-Löffler reaction for the development of a novel directed C(sp3)-H fluorination reaction which employs simple fluoride as nucleophilic fluorine source. Amine-directed installation of an alkyl-iodine center sets up the scenario for a second oxidation event which generates a key hypervalent alkyl-iodine(III) species. This crucial intermediate bearing the supernucleophuge group allow for the use of a lousy nucleophile such as fluoride for the C-F formation event. The position selectivity can be tuned by selection of the directing group. We identified two amine-based functionalities with complementary 1,5- and 1,6-HAT selectivity. This translates in a direct access to 1,3- and 1,4-fluoroamines within this fast and mild synthetic procedure.