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The catalytic hydroarylation of alkynes has emerged as an excellent methodology for the synthesis of functionalized alkenes with excellent levels of regio- and stereocontrol (syn). However, in spite of the great progress in this field, the number of asymmetric methodologies is still scarce. Herein, we report an atroposelective Ir-catalyzed C–H hydroarylation of alkynes, which enables the asymmetric synthesis of axially chiral heterobiaryl trisubstituted olefins in good to high yields and enantioselectivities up to 98% ee.

Two four-coordinate organoboron N,C-chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF-7 cells. Their excited-state properties are characterized by time-resolved pump-probe spectroscopy and fluorescence lifetime microscopy. The excited-state relaxation dynamics of the two complexes are similar when studied in DMSO. Aggregation of the complexes with the carboxylate terminal group is observed in water. When studying the light-driven excited-state dynamics of both complexes in cellulo, i. e., after being taken up into human MCF-7 cells, both complexes show different features depending on the nature of the anchoring PEG chains. The lifetime of a characteristic intramolecular charge-transfer state is significantly shorter when studied in cellulo (360±170 ps) as compared to in DMSO (∼960 ps) at 600 nm for the complexes with an amino group. However, the kinetics of the complexes with the carboxylate group are in line with those recorded in DMSO. On the other hand, the lifetimes of the fluorescent state are almost identical for both complexes in cellulo. These findings underline the importance to evaluate the excited-state properties of fluorophores in a complex biological environment in order to fully account for intra- and intermolecular effects governing the light-induced processes in functional dyes.

Two four-coordinate organoboron N,C-chelate complexes with different functional terminals on the PEG chains are studied with respect to their photophysical properties within human MCF-7 cells. Their excited-state properties are characterized by time-resolved pump-probe spectroscopy and fluorescence lifetime microscopy. The excited-state relaxation dynamics of the two complexes are similar when studied in DMSO. Aggregation of the complexes with the carboxylate terminal group is observed in water. When studying the light-driven excited-state dynamics of both complexes in cellulo, i. e., after being taken up into human MCF-7 cells, both complexes show different features depending on the nature of the anchoring PEG chains. The lifetime of a characteristic intramolecular charge-transfer state is significantly shorter when studied in cellulo (360±170 ps) as compared to in DMSO (∼960 ps) at 600 nm for the complexes with an amino group. However, the kinetics of the complexes with the carboxylate group are in line with those recorded in DMSO. On the other hand, the lifetimes of the fluorescent state are almost identical for both complexes in cellulo. These findings underline the importance to evaluate the excited-state properties of fluorophores in a complex biological environment in order to fully account for intra- and intermolecular effects governing the light-induced processes in functional dyes.

The main objective of this PhD thesis is the development of new methodologies for the synthesis of axially chiral heterobiaryls through asymmetric functionalization of this type of systems. In this regard, the approaches to achieve this goal will be based on a DYKAT (Dynamic Kinetic Asymmetric Transformation) and a desymmetrization process. Additionally, the synthesised products present a great potential in catalytic applications. In Chapter 1, which severs as an introduction, different strategies for the synthesis of axially chiral heterobiaryls are depicted, focusing on the strategies based on the catalytic asymmetric functionalization of heterobiaryls. On the other hand, in chapter 2, the first of the two developed methodologies during this PhD thesis is described. Thus, this methodology relies on a DYKAT process combined with a Buchwald-Hartwig reaction using racemic and configurationally stable heterobiaryl electrophiles. Then, this protocol has been successfully applied to the synthesis of IAN-type amines in high yields and good to excellent enantioselectivities. In chapter 3, another approach is employed for the synthesis of chiral heterobiaryls. In this case, configurationally labile substrates were desymetrized through an Ir(I)-catalyzed C-H hydroarylation. Thus, this strategy enables the synthesis of heterobiaryls with both axial and central chirality with highly regio-, diastereo- and enantioselectivities., El objetivo principal de esta tesis doctoral es el desarrollo de nuevas metodologías para la síntesis de heterobiarilos con quiralidad axial a través de la funcionalización asimétrica de este tipo de sistemas. En este sentido, las aproximaciones para cumplir este objetivo se basarán en procesos tipo DYKAT (por sus siglas en inglés: Dynamic Kinetic Asymmetric Transformation) y de desimetrización. Adicionalmente, los productos sintetizados presentan un gran potencial en aplicaciones catalíticas. En el capítulo 1, que sirve de introducción, se presentan diferentes estrategias para la síntesis de heterobiarilos con quiralidad axial, mostrando mayor atención en aquellas basadas en la funcionalización catalítica asimétrica de heterobiarilos. Por otra parte, en el capítulo 2 se describe la primera de las dos metodologías desarrolladas durante esta tesis doctoral. Así, esta metodología se basa en un proceso tipo DYKAT, combinado con la reacción de Buchwald-Hartwig, usando heterobiarilos electrófilos racémicos y configuracionalmente estables. Así, este protocolo ha podido aplicarse para la síntesis de aminas tipo IAN con altos rendimientos y de buenas a excelentes enantioselectividades. En el capítulo 3, se emplea otra aproximación para la síntesis de heterobiarilos. En este caso, sustratos configuracionalmente lábiles fueron desimetrizados a través de una hidroarilación C-H catalizada por Ir(I). Así, esta aproximación permite la síntesis de heterobiarilos con quiralidad axial y central con alta regio-, diastereo- y enantioselectividades.

The Pd-catalyzed coupling of racemic heterobiaryl bromides, triflates, or nonaflates with aryl/alkyl primary amines using QUINAP as the ligand provides the corresponding axially chiral heterobiaryl amines with excellent yields and enantioselectivities. Reactivity and structural studies of neutral and cationic oxidative addition intermediates support a dynamic kinetic asymmetric amination mechanism based on the labilization of the stereogenic axis in the latter and suggest that coordination of the amine to the Pd center is the stereodetermining step.

Seven tetracoordinate organoboron fluorophores with heterobiaryl N,O- or N,N-chelate ligands were prepared and photophysically characterized (in toluene). The electronic variation of the heteroaromatic moiety provided a means for the fine-tuning of the UV/vis absorption and emission spectra. In the most interesting cases, the spectra were red-shifted to maximum absorbance at wavelengths longer than 500 nm and emission maxima between 620 and 660 nm. The pronounced intramolecular charge-transfer character of the dyes yielded large Stokes shifts (3500-5100 cm), while maintaining appreciable fluorescence quantum yields of up to 0.2 for emission maxima longer than 600 nm. The lipophilic character of the dyes enabled their application as stains of vesicle substructures in confocal fluorescence microscopy imaging.

The Pd-catalyzed coupling of racemic heterobiaryl bromides, triflates, or nonaflates with aryl/alkyl primary amines using QUINAP as the ligand provides the corresponding axially chiral heterobiaryl amines with excellent yields and enantioselectivities. Reactivity and structural studies of neutral and cationic oxidative addition intermediates support a dynamic kinetic asymmetric amination mechanism based on the labilization of the stereogenic axis in the latter and suggest that coordination of the amine to the Pd center is the stereodetermining step.

Seven tetracoordinate organoboron fluorophores with heterobiaryl N,O- or N,N-chelate ligands were prepared and photophysically characterized (in toluene). The electronic variation of the heteroaromatic moiety provided a means for the fine-tuning of the UV/vis absorption and emission spectra. In the most interesting cases, the spectra were red-shifted to maximum absorbance at wavelengths longer than 500 nm and emission maxima between 620 and 660 nm. The pronounced intramolecular charge-transfer character of the dyes yielded large Stokes shifts (3500-5100 cm), while maintaining appreciable fluorescence quantum yields of up to 0.2 for emission maxima longer than 600 nm. The lipophilic character of the dyes enabled their application as stains of vesicle substructures in confocal fluorescence microscopy imaging.