An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Lighting the way coming and going Catalysts accelerate chemical reactions by breaking existing bonds and then forming new ones. Often, the factors that favor the first process can muddle the second one, constraining a catalyst's generality. Torres et al. found that visible light excitation of a palladium complex can facilitate both the breaking and making of carbon-halogen bonds (see the Perspective by Kathe and Fleischer). The reaction specifically forms acid chlorides by carbonylation of a wide variety of alkyl or aryl bromides and iodides. These products in turn can react further to form amides and esters. Science , this issue p. 318 ; see also p. 242
We describe herein computational studies on the unusual ability of Pd(PtBu3 )2 to catalyze formation of highly reactive acid chlorides from aryl halides and carbon monoxide. These show a synergistic role of carbon monoxide in concert with the large cone angle PtBu3 that dramatically lowers the barrier to reductive elimination. The tertiary structure of the phosphine is found to be critical in allowing CO association and the generation of a high energy, four coordinate (CO)(PR3 )Pd(COAr)Cl intermediate. The stability of this complex, and the barrier to elimination, is highly dependent upon phosphine structure, with the tertiary steric bulk of PtBu3 favoring product formation over other ligands. These data suggest that even difficult reductive eliminations can be rapid with CO association and ligand manipulation. This study also represents the first detailed exploration of all the steps involved in palladium-catalyzed carbonylation reactions with simple phosphine ligands, including the key rate-determining steps and palladium(0) catalyst resting state in carbonylations.
A palladium-catalyzed multicomponent synthetic route to polysubstituted pyrroles from aryl iodides, imines, carbon monoxide, and alkynes is described. To develop this reaction, a series of mechanistic studies on the [Pd(allyl)Cl]2/PtBu3 catalyzed synthesis of imidazolinium carboxylates from aryl iodides, imines, and carbon monoxide were first performed, including model reactions for each individual step in the transformation. These show that this reaction proceeds in a concurrent tandem catalytic fashion, and involves the in situ formation of acid chlorides, N-acyl iminium salts, and ultimately 1,3-dipoles, i.e., Münchnones, for subsequent cycloaddition. By employing a Pd(PtBu3)2/Bu4NCl catalyst, this information was used to design the first four-component synthesis of Münchnones. Coupling the latter with 1,3-dipolar cycloaddition with electron deficient alkynes or alkenes can be used to generate diverse families of highly substituted pyrroles in good yield. This represents a modular and streamlined new approach to this class of heterocycles from readily accessible starting materials.
Abstract A three component reaction between imines, aryl iodides, and carbonmonoxide is developed which delivers 1,3‐dipoles prone for cycloaddition reactions with electron‐deficient terminal as well as internal alkynes or alkenes.
A palladium-catalyzed multicomponent route to polycyclic pyrroles is described. Pd(PtBu3)2 was found to catalyze the coupling of (hetero)aryl iodides, two equivalents of carbon monoxide and alkyne-tethered imines into 1,3-dipoles (Münchnones), which undergo spontaneous, intramolecular 1,3-dipolar cycloaddition to form polycyclic pyrroles. The systematic variation of the alkyne, tethered-imine, or aryl iodide can allow the buildup of a range of pyrrole derivatives, where any of the substituents can be independently varied. In addition, the same palladium catalyst can be employed in an initial Sonogashira-type coupling with aryl iodides, which upon the addition of CO can allow the novel tandem catalytic, five component synthesis of diversely substituted products.
A palladium-catalyzed multicomponent method for the synthesis of β-lactams from imines, aryl halides, and CO has been developed. This transformation proceeds via two tandem catalytic carbonylation reactions mediated by Pd(PtBu3)2 and provides a route to prepare these products from five separate reagents. A diverse range of polysubstituted β-lactams can be generated by systematic variation of the substrates. This methodology can also be extended to the use of iodo-substituted imines to produce novel spirocyclic β-lactams in good yields and selectivity.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
