The asymmetric conjugate 1,4-addition of arylboronic acids to a,b-unsaturated carbonyl compounds is an extremely versatile and widely used organic transformation. While the rhodium(I)-catalysed reaction has been thoroughly explored, the asymmetric palladium-catalysed protocol is far less developed and understood, particularly with acyclic enones as substrates. Herein, we report the systematic evaluation of a series of metallacycles for this re-action and the conjugate addition of arylboronic acids to a wide range of a,b-unsaturated enones, catalysed by an easily accessible and robust chiral phosphapalladacycle in high yields and enantioselectivities.
Copper(II) triflate was used as a simple and commercially available catalyst in the direct amination of allylic alcohols with anilines to provide C‐allylanilines. A wide range of functional groups were tolerated under the reaction conditions, and the products were obtained regioselectivity without the need of an activator. A detailed mechanistic investigation was undertaken. The efficacy of this protocol was demonstrated in the conversion of the 2‐allylanilines into substituted quinolines through an oxidative cycloaddition reaction.
A series of optically-active pseudo-tetrahedral five-membered cyclometalated 1-naphthylethanamine iridium(III) complexes were prepared and characterized to analyze the efficacy of the stereogenic conformational lock in both solid and solution phases. The synthesis of the iridacycles was diastereoselective and the compounds were found to be conformationally rigid. When compared to its phenyl derivative, the structural lock prevented oxidation of the amine moiety within the five-membered organometallic ring during its synthesis. With up to three stereogenic centers in one of the naphthalene complexes, the stereochemistry of the metallacycle remained stable to both thermal and chemical changes. In terms of catalytic performance, the complexes displayed excellent activity for the asymmetric hydrogen transfer reaction, albeit modest enantioselectivities.
A 1,2‐dihydrophosphination of bis(phenylphosphino)ethane with a wide range of activated olefins was achieved in a catalytic manner with enantiomeric and diastereomeric excess of up to >99% and 44% respectively. The protocol can be extended to selected substrates leading to free P‐ and C‐chiral 1,2‐diphosphines. The synthesized ligands can also undergo direct complexation onto palladium affording complexes with complete retention of stereo‐integrity.
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