Benzene C−H Bond Activation in Carboxylic Acids Catalyzed by O-Donor Iridium(III) Complexes: An Experimental and Density Functional Study

The mechanism of benzene C−H bond activation by [Ir(μ-acac-O,O,C^3)(acac-O,O)(OAc)]_2 (4) and [Ir(μ-acac-O,O,C^3)(acac-O,O)(TFA)]_2 (5) complexes (acac = acetylacetonato, OAc = acetate, and TFA = trifluoroacetate) was studied experimentally and theoretically. Hydrogen−deuterium (H/D) exchange between benzene and CD_(3)COOD solvent catalyzed by 4 (ΔH^‡ = 28.3 ± 1.1 kcal/mol, ΔS^‡ = 3.9 ± 3.0 cal K^(−1) mol^(−1)) results in a monotonic increase of all benzene isotopologues, suggesting that once benzene coordinates to the iridium center, there are multiple H/D exchange events prior to benzene dissociation. B3LYP density functional theory (DFT) calculations reveal that this benzene isotopologue pattern is due to a rate-determining step that involves acetate ligand dissociation and benzene coordination, which is then followed by heterolytic C−H bond cleavage to generate an iridium-phenyl intermediate. A synthesized iridium-phenyl intermediate was also shown to be competent for H/D exchange, giving similar rates to the proposed catalytic systems. This mechanism nicely explains why hydroarylation between benzene and alkenes is suppressed in the presence of acetic acid when catalyzed by [Ir(μ-acac-O,O,C^3)(acac-O,O)(acac-C^3)]_2 (3) (Matsumoto et al. J. Am. Chem. Soc. 2000, 122, 7414). Benzene H/D exchange in CF_(3)COOD solvent catalyzed by 5 (ΔH^‡ = 15.3 ± 3.5 kcal/mol, ΔS^‡ = −30.0 ± 5.1 cal K^(−1) mol^(−1)) results in significantly elevated H/D exchange rates and the formation of only a single benzene isotopologue, (C_(6)H_(5)D). DFT calculations show that this is due to a change in the rate-determining step. Now equilibrium between coordinated and uncoordinated benzene precedes a single rate-determining heterolytic C−H bond cleavage step

DYKAT and desymmetrization strategies for the synthesis of axially chiral heterobiaryls

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

Identification of the first enantiopure Rac1–Tiam1 protein–protein interaction inhibitor and its optimized synthesis via phosphine free remote group directed hydroarylation

A phospine free hydroarylation reaction applied to norbornene derivatives is described for the first time and was exploited for the regioselective gram scale synthesis of AR-148, a known Rac1\u2013Tiam1 PPI inhibitor. Umpolung conversion of the nitro group into free amine allowed the regiocontrol of the key arylation step via a long range effect. The effect of AR-148 in comparison with its enantiomers on Rac1 activation of has been evaluated and ( 12)AR-148 has been identified as the first enantiomerically pure inhibitor of Rac1\u2013Tiam1 PPI