DFT Investigation of Suzuki-Miyaura Reactions with Aryl Sulfamates Using a Dialkylbiarylphosphine-Ligated Palladium Catalyst

Feed-Forward Neural Network for Predicting Enantioselectivity of the Asymmetric Negishi Reaction

Density functional theory (DFT) is a powerful tool to model transition state (TS) energies to predict selectivity in chemical synthesis. However, a successful multistep synthesis campaign must navigate energetically narrow differences in pathways that create some limits to rapid and unambiguous application of DFT to these problems. While powerful data science techniques may provide a complementary approach to overcome this problem, doing so with the relatively small data sets that are widespread in organic synthesis presents a significant challenge. Herein, we show that a small data set can be labeled with features from DFT TS calculations to train a feed-forward neural network for predicting enantioselectivity of a Negishi cross-coupling reaction with P-chiral hindered phosphines. This approach to modeling enantioselectivity is compared with conventional approaches, including exclusive use of DFT energies and data science approaches, using features from ligands or ground states with neural network architectures.

Broad-Scope Amination of Aryl Sulfamates Catalyzed by a Palladium Phosphine Complex

Among phenol-derived electrophiles, aryl sulfamates are attractive substrates since they can be employed as directing groups for C-H functionalization prior to catalysis. However, their use in C-N coupling is limited only to Ni catalysis. Here, we describe a Pd-based catalyst with a broad scope for the amination of aryl sulfamates. We show that the N-methyl-2-aminobiphenyl palladacycle supported by the PCyp2ArXyl2 ligand (Cyp = cyclopentyl; ArXyl2 = 2,6-bis(2,6-dimethylphenyl)phenyl) efficiently catalyzes the C-N coupling of aryl sulfamates with a variety of nitrogen nucleophiles, including anilines, primary and secondary alkyl amines, heteroaryl amines, N-heterocycles, and primary amides. DFT calculations support that the oxidative addition of the aryl sulfamate is the rate-determining step. The C-N coupling takes place through a cationic pathway in the polar protic medium.

Guided discovery of chemical reaction pathways with imposed activation

Computational power and quantum chemical methods have improved immensely since computers were first applied to the study of reactivity, but the de novo prediction of chemical reactions has remained challenging. We show that complex reaction pathways can be efficiently predicted in a guided manner using chemical activation imposed by geometrical constraints of specific reactive modes, which we term imposed activation (IACTA). Our approach is demonstrated on realistic and challenging chemistry, such as a triple cyclization cascade involved in the total synthesis of a natural product, a water-mediated Michael addition, and several oxidative addition reactions of complex drug-like molecules. Notably and in contrast with traditional hand-guided computational chemistry calculations, our method requires minimal human involvement and no prior knowledge of the products or the associated mechanisms. We believe that IACTA will be a transformational tool to screen for chemical reactivity and to study both by-product formation and decomposition pathways in a guided way.

Palladium-Catalyzed Tandem Cycloisomerization/Cross-Coupling of Carbonyl- and Imine-Tethered Alkylidenecyclopropanes

Pd0 catalysts featuring phosphorus-based monodentate ligands can detour the reactivity of carbonyl-tethered alkylidenecyclopropanes (ACPs) from standard (3+2) cycloadditions towards tandem cycloisomerization/cross-coupling processes. This new reactivity lies on the formation of key π-allyl oxapalladacyclic intermediates, which are subsequently trapped with external nucleophilic partners, instead of undergoing canonical C-O reductive eliminations. Importantly, the use of imine-tethered ACP's is also feasible. Therefore, the method provides a straightforward and stereoselective entry to a wide variety of highly functionalized cyclic alcohols and amines.

Formation of XPhos-Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross-coupling reactions. Even though the XPhos/Pd(OAc)₂ catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd⁰ complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc)₂ initially associates with the ligand to form a complex in solution, which has been characterized as Pd^II (OAc)₂ (XPhos). This Pd^II center is then reduced to the Pd⁰ (XPhos)₂ species by an intramolecular process. This study also sheds light on the formation of Pd^I -Pd^I dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd⁰ (XPhos) as the reactive species in equilibrium with the unreactive Pd⁰ (XPhos)₂ . Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides.

Aryl C–O oxidative addition of phenol derivatives to nickel supported by an N-heterocyclic carbene via a Ni0 five-centered complex

An aryl ether with the assistance of organoaluminum, an aryl sulfonate/sulfamate and an ester/carbamate proceeds towards C–O bond cleavage via a Ni⁰ five-centered complex.