La-Catalyzed Decarbonylation of Formamides and Its Applications

Diarylformamides as a Safe Reservoir and Room Temperature Source of Ultra-Pure CO in the Context of a 'Green' rWGS Reaction

Diphenylformamide 1 and bisformamide 9 are shown to be safe reservoirs and sources of CO. Their perfectly selective decarbonylations are achieved in solution at room temperature with potassium and cesium diarylamide catalysts. 1 is obtained in excellent yields directly from triethylammonium formate, which may be the product of CO2 scrubbing with NEt3 and catalytic hydrogenation. 1 thus represents a key intermediate in a low-temperature rWGS reaction sequence. Moreover, solvent-free decarbonylations of 1 may be run either in the melt at 70 °C or with 9 even in the solid state at 88 °C with improved atom economy. These simple and practical transition-metal-free decarbonylations afford ultra-pure (i. e. dry and solvent-free) CO at moderate temperatures and the diarylamines byproducts are recycled as pure compounds. In the absence of catalysts, diarylformamides 1 and 9 are long-term stable at >200 °C. DFT-calculations indicate a reaction pathway with a rate-determining deprotonation of Ph2NC(O)H and barrier-free CO elimination from Ph2NC(O)-.

Acid-Promoted Amination of Cyclohexenone for the Divergent Synthesis of p-Aminophenols and Tertiary Amines

A tunable method for the selective preparation of p-aminophenol and tertiary amines from a secondary amine and cyclohexenone has been described. Nonaromatic cyclohexenones were used as an aryl source. The desired tertiary amine products were generated when using I2 as the catalyst. This approach yields single-site-selective p-aminophenol without using I2, and the 18O labeling experiments demonstrated that hydroxyl oxygen originates from O2.

Exploiting decarbonylation and dehydrogenation of formamides for the synthesis of ureas, polyureas, and poly(urea-urethanes)

Urea derivatives, polyureas, and poly(urea-urethanes) are materials of great interest. However, their current methods of synthesis involve toxic feedstocks - isocyanate and phosgene gas. There is significant interest in developing alternative methodologies for their synthesis from safer feedstocks. We report here new methods for the synthesis of urea derivatives, polyureas, and poly(urea-urethane) using a ruthenium pincer catalyst. In this approach, urea derivatives and polyureas are synthesized from the self-coupling of formamides and diformamides, respectively, whereas poly(urea-urethanes) are synthesized from the coupling of diformamides and diols. CO and H2 gases are eliminated in all these processes. Decarbonylation of formamides using such organometallic catalysts has not been reported before and therefore mechanistic insights have been provided using experiments and DFT computation to shed light on pathways of these processes.

Lanthanide/B(C6F5)3-Promoted Hydroboration Reduction of Indoles and Quinolines with Pinacolborane

We have developed a lanthanide/B(C6F5)3-promoted hydroboration reduction of indoles and quinolines with pinacolborane (HBpin). This reaction provides streamlined access to a range of nitrogen-containing compounds in moderate to excellent yields. Large-scale synthesis and further transformations to bioactive compounds indicate that the method has potential practical applications. Preliminary mechanistic studies suggest that amine additives promote the formation of indole-borane intermediates, and the lanthanide/B(C6F5)3-promoted hydroboration reduction proceeds via hydroboration of indole-borane intermediates with HBpin and in situ-formed BH3 species, followed by the protodeborylation process.

Graphitic Carbon Nitride as Photocatalyst for the Direct Formylation of Anilines

The use of graphitic carbon nitride (g-CN) for the photocatalytic radical formylation of anilines, which represents a more sustainable and attractive alternative to the currently used approaches, is reported herein. Our operationally simple method occurs under mild conditions, employing air as an oxidant. In particular, the chemistry is driven by the ability of g-CN to reach an electronically excited state upon visible-light absorption, which has a suitable potential energy to trigger the formation of reactive α-amino radical species from anilines. Mechanistic investigations also proved the key role of the g-CN to form reactive superoxide radicals from O2 via single electron transfer. Importantly, this photocatalytic transformation provides a variety of functionalized formamides (15 examples, up to 89 % yield).

Manganese catalysed dehydrogenative synthesis of polyureas from diformamide and diamines

We report here the synthesis of polyureas from the dehydrogenative coupling of diamines and diformamides. The reaction is catalysed by a manganese pincer complex and releases H2 gas as the only by-product making the process atom-economic and sustainable. The reported method is greener in comparison to the current state-of-the-art production routes that involve diisocyanate and phosgene feedstock. We also report here the physical, morphological, and mechanical properties of synthesized polyureas. Based on our mechanistic studies, we suggest that the reaction proceeds via isocyanate intermediates formed by the manganese catalysed dehydrogenation of formamides.

Lanthanide-catalyzed deamidative cyclization of secondary amides and ynones through tandem C-H and C-N activation

The tandem inert α-C-H and C-N bond activation of amides represents a highly valuable but challenging transformation in organic synthesis. Herein, a simple rare earth metal amido complex has been shown to catalyse unprecedented cyclization of amides with ynones to form trisubstituted 2-pyrones. This protocol significantly enables the selective merger of inert α-C-H and C-N bond activations of amides and indicates a particular role of rare earth catalysts in enhancing the selectivity for the α-C-H bond of amides in the presence of N-H bonds.

Controllable carbonyl-assisted C(sp3)–C(sp3) bond reduction and reorganization

Unprecedentedly preferential reduction of unstrained C(sp3)–C(sp3) bond over ketone, hydrogenative [2+2+2]-cycloreversion of 2,4-diacylcyclohexanols, and cyclizative degradation of poly(vinylketone) have been achieved by organolanthanide catalysis.