A Palladium-Catalyzed Carbonylative-Deacetylative Sequence to 1,3-Keto Amides

Palladium-catalyzed enantioselective carbonylation reactions

Carbonylation, one of the most powerful approaches to the preparation of carbonylated compounds, has received significant attention from researchers active in various fields. Indeed, impressive progress has been made on this subject over the past few decades. Among the various types of carbonylation reactions, asymmetric carbonylation is a straightforward methodology for constructing chiral compounds. Although rhodium-catalyzed enantioselective hydroformylations have been discussed in several elegant reviews, a general review on palladium-catalyzed asymmetric carbonylations is still missing. In this review, we summarize and discuss recent achievements in palladium-catalyzed asymmetric carbonylation reactions. Notably, this review’s contents are categorized by reaction type.

Enantioselective α-Carbonylative Arylation for Facile Construction of Chiral Spirocyclic β,β'-Diketones

We herein describe the first enantioselective α-carbonylative arylation, providing a diverse set of chiral spiro β,β'-diketones bearing various ring sizes and functionalities in high yields and good to excellent enantioselectivities. Calculations suggest the transformation proceeds through reductive elimination instead of nucleophilic addition pathway.

COtab: Expedient and Safe Setup for Pd-Catalyzed Carbonylation Chemistry

Bench-stable tablets (COtabs) have been developed for the rapid and safe production of carbon monoxide. The tablets can be made in less than 5 min without the use of a glovebox and only require a stock solution of an amine base to liberate a specific quantity of CO in a two-chamber system. The COtabs were tested in five different carbonylation reactions and provided similar yields compared to literature procedures. Finally, a gram-scale reaction was conducted, as well as ¹³C-isotope labeling of the anticancer drug, olaparib.

Computational Exploration of Mechanistic Avenues in C-H Activation Assisted Pd-Catalyzed Carbonylative Coupling

The detailed mechanism of the intermolecular Pd-catalyzed carbonylative coupling reaction between aryl bromides and polyfluoroarenes relying on C(sp²)-H activation was investigated using state-of-the-art computational methods (SMD-B3LYP-D3(BJ)/BS2//B3LYP-D3/BS1). The mechanism unveils the necessary and important roles of a slight excess of carbon monoxide: acting as a ligand in the active catalyst state, participating as a reactant in the carbonylation process, and accelerating the final reductive elimination event. Importantly, the desired carbonylative coupling route follows the rate-limiting C-H activation process via the concerted metalation-deprotonation pathway, which is slightly more feasible than the decarboxylative route leading to byproduct formation by 1.2 kcal/mol. The analyses of the free energies indicate that the choice of base has a significant effect on the reaction mechanism and its energetics. The Cs₂CO₃ base guides the reaction toward the coupling route, whereas carbonate bases such as K₂CO₃ and Na₂CO₃ switch toward an undesired decarboxylative path. However, K₃PO₄ significantly reduces the C-H activation barrier over the decarboxylation reaction barrier and can act as a potential alternative base. The positional influence of a methoxy substituent in bromoanisole and different substituent effects in polyfluoroarenes were also considered. Our results show that different substituents impose significant impact on the desired carbonylative product formation energetics. Considering the influence of several ligands leads to the conclusion that other phosphine and N-heterocyclic carbene, such as P ⁿBuAd₂ and IMes, can be used as an efficient alternative than the experimentally reported P ^tBu₃ ligand exhibiting a clear preference for C-H activation (ΔΔ^⧧ G_L^S) by 7.1 and 10.9 kcal/mol, respectively. We have also utilized the energetic span model to interpret the experimental results. Moreover, to elucidate the origin of activation barriers, energy decomposition analysis calculations were accomplished for the critical transition states populating the energy profiles.

The Development and Application of Two-Chamber Reactors and Carbon Monoxide Precursors for Safe Carbonylation Reactions

Low molecular weight gases (e.g., carbon monoxide, hydrogen, and ethylene) represent vital building blocks for the construction of a wide array of organic molecules. Whereas experimental organic chemists routinely handle solid and liquid reagents, the same is not the case for gaseous reagents. Synthetic transformations employing such reagents are commonly conducted under pressure in autoclaves or under atmospheric pressure with a balloon setup, which necessitates either specialized equipment or potentially hazardous and nonrecommended installations. Other safety concerns associated with gaseous reagents may include their toxicity and flammability and, with certain gases, their inability to be detected by human senses. Despite these significant drawbacks, industrial processes apply gaseous building blocks regularly due to their low cost and ready availability but nevertheless under a strictly controlled manner. Carbon monoxide (CO) fits with all the parameters for being a gas of immense industrial importance but with severe handling restrictions due to its inherent toxicity and flammability. In academia, as well as research and development laboratories, CO is often avoided because of these safety issues, which is a limitation for the development of new carbonylation reactions. With our desire to address the handling of CO in a laboratory setting, we designed and developed a two-chamber reactor (COware) for the controlled delivery and utilization of stoichiometric amounts of CO for Pd-catalyzed carbonylation reactions. In addition to COware, two stable and solid CO-releasing molecules (COgen and SilaCOgen) were developed, both of which release CO upon activation by either Pd catalysis or fluoride addition, respectively. The unique combination of COware with either COgen or SilaCOgen provides a simple reactor setup enabling synthetic chemists to easily perform safe carbonylation chemistry without the need for directly handling the gaseous reagent. With this technology, an array of low-pressure carbonylations were developed applying only near stoichiometric amounts of carbon monoxide. Importantly, carbon isotope variants of the CO precursors, such as (13)COgen, Sila(13)COgen, or even (14)COgen, provide a simple means for performing isotope-labeling syntheses. Finally, the COware applicability has been extended to reactions with other gases, such as hydrogen, CO2, and ethylene including their deuterium and (13)C-isotopically labeled versions where relevant. The COware system has been repeatedly demonstrated to be a valuable reactor for carrying out a wide number of transition metal-catalyzed transformations, and we believe this technology will have a significant place in many organic research laboratories.

Recent advances in the transition metal catalyzed carbonylation of alkynes, arenes and aryl halides using CO surrogates

Transition metal catalyzed carbonylation reactions using carbon monoxide as the C-1 source have occupied an all important position in catalysis which is subsequently related to organic synthesis and industrial synthesis of molecules.