Manganese-Mediated Reductive Transamidation of Tertiary Amides with Nitroarenes

Amides are an important class of organic compounds, which have widespread industrial applications. Transamidation of amides is a convenient method to generate new amides from existing ones. Tertiary amides, however, are challenging substrates for transamidation. Here we describe an unconventional approach to the transamidation of tertiary amides using nitroarenes as the nitrogen source under reductive conditions. Manganese metal alone mediates the reactions and no additional catalyst is required. The method exhibits broad scope and high functional group tolerance.

Amide synthesis via nickel-catalysed reductive aminocarbonylation of aryl halides with nitroarenes

Chi Wai Cheung, Xile Hu, Marten Leendert Ploeger

Aminocarbonylation of aryl halides is one of the most useful methods in amide synthesis, but nitroarenes have not been used as a nitrogen source in this method even though they are more economical and accessible than anilines. Reported here is the development of nickel catalysis for the first three-component reactions of aryl halides, Co2(CO)8, and nitroarenes under reductive conditions to produce aryl amides. A wide range of (hetero)aryl iodides and bromides as well as nitro(hetero)arenes are suitable reaction partners, and high functional group compatibility has been achieved. The method might be used for the streamlined synthesis of aryl amides.

2018

Nickel-catalyzed Hydrosilylation of Alkenes and Transition-Metal-Free Intermolecular α-C-H Amination of Ethers

Ivan Buslov

Transition-metal-catalyzed hydrosilylation of olefins is one of the most important methods for the preparation of organosilicon compounds, which have broad applications in both synthetic and material chemistry. For decades, precious metals, principally platinum-based complexes, have been utilized as catalysts for olefin hydrosilylation. However, due to the high and volatile cost and low abundance of Pt, the development of active and selective catalysts based on Earth-abundant metals is highly desirable. In the first chapter, a short overview of state-of-the-art Pt catalysts and recent advances in development of Fe, Co and Ni-catalysts for olefin hydrosilylation is given. The applications, mechanisms and remaining challenges of transition-metal-catalyzed hydrosilylation are discussed. In the chapter 2, chemoselective anti-Markovnikov hydrosilylation of functionalized alkenes using well-defined bis(amino)amide nickel pincer complexes is described. The catalysts exhibit both high turnover frequencies and turnover numbers. Alkenes containing amino, ester, amido, ketone, and formyl groups are selectively hydrosilylated with Ph2SiH2. Chemoselective hydrosilylation of carbon-carbon double bond in the presence of formyl group using a base metal catalyst is reported for the first time. A modification of reaction conditions allows tandem isomerization-hydrosilylation reactions of internal alkenes to give terminal alkyl silanes. Hydrosilylation of alkenes with tertiary silanes is more attractive from practical point of view. The screening of various nickel alkoxide complexes with reduced steric bulk led us to discovery of an efficient heterogeneous catalyst for alkene hydrosilylation with commercially relevant tertiary silanes (chapter 3). The catalyst exhibits high activity in anti-Markovnikov hydrosilylation of unactivated terminal alkenes and isomerizing hydrosilylation of internal alkenes. The catalyst can be applied to synthesize a single terminal alkyl silane from a mixture of internal and terminal alkene isomers. Furthermore, the same catalyst can be used to remotely functionalize an internal alkene derived from a fatty acid. Chapter 4 describes a catalytic system composed of a nickel amido(bisoxazoline) complex and NaOtBu for an unexpected synthetic transformation, leading to the synthesis of functionalized alkyl hydrosilanes from readily available alkenes and alkoxysilanes. This method provides a convenient and safe alternative to hydrosilylation using flammmable and potentially dangerous Me2SiH2, MeSiH3 and SiH4. The reaction mechanism was also described. Efficient and atom-economical creation of C-N bond is one of the major tasks in synthetic organic chemistry. Direct C-H amination has emerged as an attractive method for the construction of new C-N bonds. In the chapter 5 a new transition-metal free method for the intermolecular amination of the alpha-C-H bonds of ethers is described. Using a hypervalent iodine reagent as oxidant the amination of cyclic and acyclic alkyl ethers with a wide range of amides, imides, and amines was achieved. The utility of this method was demonstrated in the synthesis of Tegafur and its analogues. This transition-metal-free method provides a rapid access to a large number of nitrogen-containing organic molecules that may serve as useful synthetic intermediates or biologically active agents.

EPFL2016

Lewis acid Catalyzed Annulations of Donor-Acceptor Aminocyclopropanes and Aminocyclobutanes

Sophie Lucie Racine

Organic molecules are indispensable have greatly contributed to the confort of our modern life. Nevertheless, humanity is facing now new challenges such as environmental issues and emerging drug resistances. In order to solve these major concerns, chemists are aiming to develop environmental friendly synthetic methods leading more efficiently to complex molecules with new biological modes of action. Nitrogen substituted five and six membered rings are rigid ubiquitous molecules in nature. In particular, these motives are found in DNA, natural products, as well as top selling drugs. Amongst all, the sought after nucleoside analogs, sulfur substituted cyclopentylenamines and Aspidosperma alkaloids, are based on tetrahydrofuryl-, cyclopentyl- and cyclohexyl-amines. A new approach to the synthesis of nitrogen substituted five and six membered rings would be highly valued. Annulations and cycloadditions are convergent synthetic methods, which are providing complex cyclic molecules from simple starting materials. Particularly, strain rings such as DA-cyclopropanes have been reported as efficient dipoles in annulation, providing saturated five membered ring molecules. Analogously, the use of phthalimide donor-acceptor cyclopropanes in [3+2] annulation with various dipolarophile was studied in our group to afford cyclopentylamines and tetrahydrofurylamines. In this thesis, a new Lewis acid catalyzed formal [3+2] cycloaddition between nucleobase donor-acceptor cyclopropanes and dipolarophiles such as ketones, aldehydes and silyl enolethers is applied to the synthesis of potentially bioactive nucleoside and carbonucleoside analogs. Pyrimidines donor-acceptor cyclopropanes were suitable dipoles in the [3+2] annulation, while purines were inert. This methodology was further extended to the synthesis of six membered ring nucleoside derivatives via a formal [4+2] cycloaddition of nucleobase donor-acceptor cyclobutanes and aldehydes. The [3+2] annulation of donor-acceptor cyclopropanes was further investigated and optimized with thioalkynes as dipolarophiles, providing a useful tool for the synthesis of sulfur substituted cyclopentenylamines. Interestingly, during the studies of the [3+2] annulation an unprecedented reactivity of the phthalimide donor-acceptor cyclopropane, involving the carbonyl of the phthalimide and the formation of an oxonium intermediate, leading to complex polycyclic iso-oxindole was discovered. The transformation was further optimized and tolerated a large variety of functional groups. Studies towards the total synthesis of Aspidospermidine and by extension to Aspidosperma alkaloids were performed using a convergent [2+2+2] annulation cascade strategy or alternatively via consecutive [2+2] and [4+2] annulations. This thesis brings new insights on the reactivity of DA-aminocyclopropanes and DA-aminocyclobutanes in presence of Lewis acid catalysts. The development of novel formal cycloaddition of DA-aminocyclopropanes and DA-aminocyclobutanes were successfully achieved providing an efficient routes for the synthesis of valuable nitrogen substituted five or 6 membered rings such as (carbo)nucleoside analogs, sulfur cyclopentylenamines and polycyclic iso-oxindoles. In addition, preliminary results were obtained concerning the [2+2+2] cascade annulation strategy for the synthesis Aspidosperma alkaloids.

EPFL2016

Lewis acid Catalyzed Annulations of Donor-Acceptor Aminocyclopropanes and Aminocyclobutanes

Sophie Lucie Racine

EPFL2016

Nickel-catalyzed Hydrosilylation of Alkenes and Transition-Metal-Free Intermolecular α-C-H Amination of Ethers

Ivan Buslov

EPFL2016