The borrowing hydrogen (BH) principle, also called hydrogen auto-transfer, is a powerful approach which combines transfer hydrogenation (avoiding the direct use of molecular hydrogen) with one or more intermediate reactions to synthesize more complex molecules without the need for tedious separation or isolation processes. The strategy which usually relies on three steps, (i) dehydrogenation, (ii) intermediate reaction, and (iii) hydrogenation, is an excellent and well-recognized process from the synthetic, economic, and environmental point of view. In this context, the objective of the present review is to give a global overview on the topic starting from those contributions published prior to the emergence of the BH concept to the most recent and current research under the term of BH catalysis. Two main subareas of the topic (homogeneous and heterogeneous catalysis) have been identified, from which three subheadings based on the source of the electrophile (alkanes, alcohols, and amines) have been consid...

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Advances in One-Pot Synthesis through Borrowing Hydrogen Catalysis

1,2,3-Triazole-containing hybrids as leads in medicinal chemistry: A recent overview

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An Introduction To Medicinal Chemistry

Recently, samarium(II) iodide reductants have emerged as powerful single electron donors for the highly chemoselective reduction of common functional groups. Complete control of the product formation can be achieved on the basis of a judicious choice of a Sm(II) complex/proton donor couple, even in the presence of extremely sensitive functionalities (iodides, aldehydes). In most cases, the reductions are governed by thermodynamic control of the first electron transfer, which opens up new prospects for unprecedented transformations via radical intermediates under mild regio-, chemo- and diastereoselective conditions that are fully orthogonal to hydrogenation or metal-hydride mediated processes.

Recent advances in the chemoselective reduction of functional groups mediated by samarium(II) iodide: a single electron transfer approach.

Highly chemoselective direct reduction of primary, secondary, and tertiary amides to alcohols using SmI2/amine/H2O is reported. The reaction proceeds with C–N bond cleavage in the carbinolamine intermediate, shows excellent functional group tolerance, and delivers the alcohol products in very high yields. The expected C–O cleavage products are not formed under the reaction conditions. The observed reactivity is opposite to the electrophilicity of polar carbonyl groups resulting from the nX → π*C═O (X = O, N) conjugation. Mechanistic studies suggest that coordination of Sm to the carbonyl and then to Lewis basic nitrogen in the tetrahedral intermediate facilitate electron transfer and control the selectivity of the C–N/C–O cleavage. Notably, the method provides direct access to acyl-type radicals from unactivated amides under mild electron transfer conditions.

Highly Chemoselective Reduction of Amides (Primary, Secondary, Tertiary) to Alcohols using SmI2/Amine/H2O under Mild Conditions

The ruthenium-catalyzed azide alkyne cycloaddition (RuAAC) affords 1,5-disubstituted 1,2,3-triazoles in one step and complements the more established copper-catalyzed reaction providing the 1,4-isomer. The RuAAC reaction has quickly found its way into the organic chemistry toolbox and found applications in many different areas, such as medicinal chemistry, polymer synthesis, organocatalysis, supramolecular chemistry, and the construction of electronic devices. This Review discusses the mechanism, scope, and applications of the RuAAC reaction, covering the literature from the last 10 years.

https://research.chalmers.se/publication/246752/file/246752_Fulltext.pdf

Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications.

Hydrogen borrowing provides an efficient and atom economical method for carbon–nitrogen and carbon–carbon bond formation from alcohol precursors. Glycerol is a renewable nontoxic polyol and a potential precursor to small functional organic molecules. We here report the direct amination of solketal, a 1,2-hydroxy-protected derivative of glycerol, via ruthenium-catalyzed hydrogen borrowing, affording up to 99% conversion and 92% isolated yield using [Ru(p-cymene)Cl2]2 as the catalyst precursor. The synthesis of an antitussive agent in 86% overall yield from solketal was also demonstrated using this methodology.

Glycerol Upgrading via Hydrogen Borrowing: Direct Ruthenium-Catalyzed Amination of the Glycerol Derivative Solketal

1,4- and 1,5-Disubstituted triazole amino acid monomers have gained increasing interest among peptidic foldamers, as they are easily prepared via Cu- and Ru-catalyzed click reactions, with the potential for side chain variation. While the latter is key to their applicability, the synthesis and structural properties of the chiral mono- or disubstituted triazole amino acids have only been partially addressed. We here present the synthesis of all eight possible chiral derivatives of a triazole monomer prepared via a ruthenium-catalyzed azide alkyne cycloaddition (RuAAC). To evaluate the conformational properties of the individual building units, a systematic quantum chemical study was performed on all monomers, indicating their capacity to form several low energy conformers. This feature may be used to effect structural diversity when the monomers are inserted into various peptide sequences. We envisage that these results will facilitate new applications for these artificial oligomeric compounds in diverse areas, ranging from pharmaceutics to biotechnology.

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Chiral 1,5-disubstituted 1,2,3-triazoles - versatile tools for foldamers and peptidomimetic applications.

Selective cleavage of 3,5-bis-(trifluoromethyl)benzylcarbamate by SmI2-Et3N-H2O.

To a large extent, organic building blocks are today obtained from petroleum-based products From an environmental point of view, biomass-derived compounds are more sustainable alternatives to such oil-derived molecules The 12 principles of green chemistry describe how chemical processes can be improved in terms of sustainability With some of these principles as guidelines, this thesis considers the upgrading of renewable glycerol- and amino acid-derived compounds using two different atom economic catalytic reactions: the hydrogen borrowing reaction, and the ruthenium-catalysed azide-alkyne cycloaddition (RuAAC) reaction First, the glycerol derivatives solketal and 1,3-propanediol were investigated as starting materials in organic transformations using hydrogen borrowing methodology Solketal was aminated with a set of secondary amines as well as sterically hindered primary amines, yielding the corresponding amino glycerol derivatives in good to excellent yields, using [Ru( p -cymene)Cl 2 ] 2 as the catalyst Deprotection of the acetal gave the free amino diol, and this reaction sequence was used to synthesise the antitussive agent dropropizine in two steps from solketal Furthermore, the iridium-catalysed α-alkylation of acetophenone with 1,3-propanediol was investigated A mixture of products was obtained in moderate yields when using [Ir(cod)Cl] 2 as the catalyst, while the selectivity could be improved by instead utilising an iridium-carbene complex as the catalyst Hydrogen transfer methodology was also employed in the synthesis of chromanone scaffolds from 2’-hydroxyacetophenone and an alcohol Brief mechanistic insight was gained considering the two reaction types via deuterium-labelling experiments and computational techniques, respectively In addition, chiral triazole δ-amino acids were constructed via a RuAAC reaction for the construction of foldamers Eight chiral triazoles were synthesized in good yields Computational conformational studies revealed that the synthesised monomers had several low energy conformations that could be part of a well-defined three-dimensional foldameric structure Finally, the RuAAC reaction was used in combination with a hydrogen borrowing cyclisation reaction for the construction of 1,5-fused triazole piperazines from a simple amino acid derived azide A set of 14 different triazoles were synthesised in moderate to excellent yields, and 7 of these triazoles were successfully cyclised to give the desired 1,5-fused triazoles in two steps

https://publications.lib.chalmers.se/records/fulltext/249368/249368.pdf

Valorisation of Renewable Building Blocks via Transition Metal Catalysis – Glycerol- and Amino Acid Derived Compounds in Hydrogen Borrowing and RuAAC Reactions

Anna Said Stålsmeden

Papers

Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications.

Glycerol Upgrading via Hydrogen Borrowing: Direct Ruthenium-Catalyzed Amination of the Glycerol Derivative Solketal

Chiral 1,5-disubstituted 1,2,3-triazoles - versatile tools for foldamers and peptidomimetic applications.

Selective cleavage of 3,5-bis-(trifluoromethyl)benzylcarbamate by SmI2-Et3N-H2O.

Valorisation of Renewable Building Blocks via Transition Metal Catalysis – Glycerol- and Amino Acid Derived Compounds in Hydrogen Borrowing and RuAAC Reactions