Iridium/Chiral Diene-Catalyzed Asymmetric 1,6-Addition of Arylboroxines to α,β,γ,δ-Unsaturated Carbonyl Compounds

Abstract

Iridium-catalyzed asymmetric 1,6-addition of arylboroxines to alpha,beta,gamma,delta-unsaturated carbonyl compounds to give delta-arylated carbonyl compounds in high yields with 90-99% enantioselectivity was realized by use of an iridium/chiral diene complex.

Catalytically Active Species in Copper/DiPPAM‐Catalyzed 1,6‐Asymmetric Conjugate Addition of Dialkylzinc to Dienones: A Computational Overview

“…Let us nevertheless notice that the strong binding of the carbonyl compound in I 6 is associated with a large entropic loss compared to I J , for which more degrees of freedom of the carbonyl chain are kept. As a consequence, similar Gibbs energies with respect to separated reactants were found for I 6 and I J (7.2 kcal mol À 1 ). Discrimination between these two mechanisms thus originated from kinetic factors.…”

“…An additional binding is observed as the C=C bond of 1 a comes into interaction through a π-bond with the Cu(I) center, resulting in intermediate I 4 when 1,4-conjugate addition is examined, and I 6 in the case of 1,6conjugate addition. I 6 and I 0 intermediates are in equilibrium as they are isoergonic, with an exchange between the two structures exhibiting a Gibbs free energy equal to 13 kcal mol À 1 which proved to be lower than the CÀ C bond formation step. In contrast, I 4 is found to be significantly destabilized (Δ r G = + 7.2 kcal mol À 1 ) and its formation is disfavored (TS π4 higher than CÀ C bond formation in TS C-C6 ).…”

“…However, 1,6-ACA has been described with a range of electrophiles, nucleophiles, metal-based catalysts, and chiral ligands families. [3][4][5][6][7][8][9] Mauduit et al have developed an efficient chiral tridentate P,N,O ligand, named diphenylphosphinoazomethinylate salt (DiPPAM, L), [10] which has proved its efficiency for copper-catalyzed 1,6-ACA of dialkylzinc reagents to cyclic [5,7] and more recently to acyclic [11][12][13] dienones (Scheme 1). While good to excellent regioselectivity and enantioselectivity could be achieved with this catalytic system, attempts to characterize intermediates were unsuccessful and the active catalytic species has remained unidentified.…”

Catalytic enantioselective 1,6-conjugate additions of propargyl and allyl groups

“…However, catalytic enantioselective 1,6-conjugate additions are uncommon, and ones that are able to incorporate readily functionalizable moieties, such as propargyl or allyl groups, into acyclic α,β,γ,δ-doubly unsaturated acceptors are unknown 2 . Chemical transformations that could generate a new bond at the C6 position of a dienoate are particularly desirable, as the resulting products would be subjected to further modifications; such reactions, especially when dienoates contain two equally substituted olefins, are scarce 3 and are confined to reactions promoted by a phosphine–copper (with alkyl Grignard 4,5 , dialkylzinc or trialkylaluminum compounds 6,7 ), a diene–iridium (with arylboroxines) 8,9 , and a bisphosphine–cobalt catalyst (with monosilyl-acetylenes) 10 . 1,6-conjugate additions are otherwise limited to substrates where there is full substitution at C4 11 .…”

Development of Bicyclo[3.3.0]octadiene- or Dicyclopentadiene-Based Chiral Diene Ligands for Transition-Metal-Catalyzed Reactions

“…13 As for iridium-catalyzed reactions, these ligands have been applied in the kinetic resolution of allyl carbonates, 6 the annulation of 1,3-dienes with (2-formylphenyl)boron reagents, 14 and the 1,6-addition of arylboroxines to a,b,g,d-unsaturated carbonyl compounds. 15 In 2007, our group reported a family of unique chiral diene ligands bearing an nonbridged bicyclo[3.3.0]octadiene backbone, i.e. compounds 5.…”