A New Chiral P,N-Ligand Derived from 1-Phenylphospholane-2-carboxylic Acid (Phenyl-P-proline) for Palladium-Catalyzed Asymmetric Allylic Substitution Reactions

A readily accessible and modular carbohydrate-derived thioether/selenoether-phosphite ligand library for Pd-catalyzed asymmetric allylic substitutions

A large library of thioether/selenoether-phosphite ligands have been tested in the Pd-catalyzed asymmetric allylic substitution reaction. The presented ligands are derived from cheap and available carbohydrates and they are air-stable solids and easy to handle. Their highly modular nature has made it possible to achieve excellent enantioselectivities in the substitution of a range of hindered and unhindered substrates (ees up to 99% and 91%, respectively). In addition, twelve C-, N- and O-nucleophiles can be efficiently introduced, independently of their nature. Among the whole library, ligands that contain an additional chiral centre in the alkyl backbone chain next to the phosphite group and an enantiopure biaryl phosphite group provided the best enantioselectivities. In general, there is a cooperative effect between these two chiral elements, and therefore, a matched combination between them is necessary to achieve the highest enantioselectivities. However, in the case of cyclic substrates, this cooperative effect is less pronounced and advantageously, both enantiomers of the product can be obtained by setting up the desired configuration of the biaryl phosphite group. Studies of the key Pd-π-allyl intermediates allowed us to better understand the enantioselectivities obtained experimentally.

P-Stereogenic β-Aminophosphines: Preparation and Applications in Enantioselective Organocatalysis

The synthesis of stereodefined β-aminophosphines having both carbon- and phosphorus-based chirality centers is described. The method involves resolution of a mixture of β-aminophosphine oxide diastereomers accessed by ring-opening of an amino alcohol-derived cyclic sulfamidate. A stereospecific, borane-promoted reduction of β-aminophosphine oxides, which occurs under mild conditions and with inversion of configuration at phosphorus, is a key step in this process. The products obtained are new building blocks for the synthesis of P-chiral ligands and organocatalysts. In a proof-of-concept application in organocatalysis, the diastereomeric P-chiral β-aminophosphine-based bifunctional thioureas displayed significantly different activities in the Morita-Baylis-Hillman reaction of methyl acrylate with benzaldehyde derivatives.

Metal-catalyzed enantioselective allylation in asymmetric synthesis

Metal-catalyzed enantioselective allylation, which involves the substitution of allylic metal intermediates with a diverse range of different nucleophiles or S(N)2'-type allylic substitution, leads to the formation of C-H, -C, -O, -N, -S, and other bonds with very high levels of asymmetric induction. The reaction may tolerate a broad range of functional groups and has been applied successfully to the synthesis of many natural products and new chiral compounds.

The effect of P-cyclohexyl groups on the coordination chemistry of phosphaguanidinates

The anion of P-dicyclohexylphosphaguanidine, Cy2PC{NiPr}{NHiPr}, forms a P,N-chelate at lithium and cobalt(II); bridging through the Nimine atom forms cyclic hexamers in the former complex.