One‐Pot Three‐Component Catalytic Enantioselective Synthesis of Homoallylboronates

Abstract

In Gegenwart luftstabiler Kupfersalze und eines einfachen chiralen Amins als Cokatalysator reagieren Bis(pinacolato)dibor, Enale und 2‐(Triphenylphosphoranyliden)acetate in einer Sequenz aus katalytischer asymmetrischer konjugierter Boranaddition und Wittig‐Reaktion hoch enantioselektiv zu Homoallylboronsäureestern (siehe Schema).

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

“…496,516−521 Enantioselective borylation of α,β-unsaturated aldehydes has been employed in tandem with a Wittig reaction to provide access to homoallylboronates (Scheme 61). 522 The amine cocatalyst is proposed to activate the substrate to nucleophilic attack by transiently generating a chiral iminium cation from the aldehyde group. Asymmetric copper(I)catalyzed borylation of α-dehydroamino acid derivatives was used to afford chiral β-hydroxy-α-amino acids.…”

Highly Enantioselective Cascade Transformations by Merging Heterogeneous Transition Metal Catalysis with Asymmetric Aminocatalysis

“…Thus, the design and discovery of novel cooperative catalytic systems to conquer this challenge are particularly pressing. In 2006, we discovered that C-C bond formation could be achieved by combining homogeneous transition-metal catalysis with aminocatalysis, and have since then developed dual catalytic systems for reactions, such as enantioselective α-allylic alkylaion of various carbonyl compounds 11 12 , enantioselective β-alkylation of α,β-unsaturated aldehydes 13 , carbocyclizations of various enynes 14 15 and for the synthesis of homoallylboronates 16 . While successful, this methodology still suffers from drawbacks, the main being related to the use of homogeneous catalysts that are tedious to remove, resulting in inefficient separation, purification and recycling of the catalyst 17 18 19 20 21 .…”

Chiral Copper(II)‐Catalyzed Enantioselective Boron Conjugate Additions to α,β‐Unsaturated Carbonyl Compounds in Water

“…In addition to the use of water as a solvent, Cu II catalysis is very rare in the boron conjugate addition to α,β‐unsaturated carbonyl compounds 9. 16 Indeed, 1,4‐addition of diboron to α,β‐unsaturated carbonyl compounds has been catalyzed by Cu I in organic solvents in many cases 7. 8 On the other hand, whereas Cu(OH) 2 was found to be very effective in water, the activity of Cu I is not clear, because Cu I species are known to be unstable in water 17.…”