Recent Developments in C–C Bond Formation Using Catalytic Reductive Coupling Strategies

Abstract

Metal-catalyzed reductive coupling processes have emerged as a powerful methodology for the introduction of molecular complexity from simple starting materials. These methods allow for an orthogonal approach to that of redox-neutral strategies for the formation of C–C bonds by enabling cross-coupling of starting materials not applicable to redox-neutral chemistry. This short review summarizes the most recent developments in the area of metal-catalyzed reductive coupling utilizing catalyst turnover by a stoichiometric reductant that becomes incorporated in the final product.1 Introduction2 Ni Catalysis3 Cu Catalysis4 Ru, Rh, and Ir Catalysis4.1 Alkenes4.2 1,3-Dienes4.3 Allenes4.4 Alkynes4.5 Enynes5 Fe, Co, and Mn Catalysis6 Conclusion and Outlook

Studies Toward Improved Enantiocontrol in the Asymmetric Cu-Catalyzed Reductive Coupling of Ketones and Allenamides: 1,2-Aminoalcohol Synthesis

“…Since the classical work of Barrett, who generated preformed chiral N -substituted allylic boron reagents of 1 based on the Brown IPC-borane system, the Krische group elegantly applied their catalytic reductive coupling through hydrogen autotransfer technology to the catalytic aminoallylation of aldehydes using Ru- , or Ir-catalysis . In contrast, with ketone electrophiles it is typically more challenging to achieve highly enantioselective processes relative to aldehydes due to their decreased reactivity and the reduced steric differentiation between the two ketone substituents.…”

Aminoalcohol Synthesis through Nonprecious Metal Catalysis: Enantioselective Cu-Catalyzed Reductive Coupling of Aldehydes and Allenamides

“…Arguably, one of the most powerful methods in organic synthesis is the reductive allylation of carbonyl electrophiles using unsaturated hydrocarbons (Scheme ). This area has largely been pioneered by the Krische group utilizing allenes ( 1 ) (Scheme A), enynes, or 1,3-dienes as the allyl nucleophile precursors with H 2 or a H 2 surrogate as the terminal reductant. While these processes are transformative, they require the use of precious metal catalysts derived from Ir, Rh, or Ru.…”

“…More recently, the Buchwald group has developed Cu-catalyzed versions of these processes utilizing silane as the terminal reductant (Scheme B) that are attractive due to the low cost, low toxicity, and high availability of Cu. Notably, the techniques of Krische (Scheme A) and Buchwald (Scheme B) are orthogonal, whereby precious metal-catalyzed reductive allylation primarily works well with aldehydes, with numerous published examples, − whereas ketones are more problematic, with only four known examples , (Scheme A). In contrast, the Cu-catalyzed processes work well with ketone electrophiles, − yet aldehydes are problematic (two reported examples) , due to competitive reduction of the aldehyde by the CuH catalyst (Scheme B).…”

Cobalt(I)-Catalyzed Reductive Cyclization of Enynes and Diynes Using Hydrogen Gas as a Reductant

“…Reductive coupling between two different π components (e.g., alkenes, alkynes, and carbonyl groups) is one of the unique reactions catalyzed by transition-metal catalysts . Reductive cyclization between diynes or an alkyne and an alkene is a promising methodology for the regio- and stereoselective construction of cyclic compounds.…”

“…A cationic Co­(I) catalyst 7 was formed from the reduction of CoBr 2 ·6H 2 O by Zn in the presence of a ligand and NaBAr F 4 . Oxidative addition of substrate 1 to Co­(I) catalyst 7 produced cobaltacycle intermediate I , which is a common intermediate in reductive cyclization catalyzed by a transition-metal catalyst. − Then, σ-bond metathesis between I and H 2 occurred to give intermediate II , , from which reductive elimination afforded product 2 along with the regeneration of Co­(I) catalyst 7 . We speculate that a Xantphos-type ligand operates as a tridentate ligand in this reaction, which results in the prevention of side reactions such as isomerization and over-reduction by occupation of three coordination sites on the cobalt center …”