Enantioselective Isomerization of Primary Allylic Alcohols into Chiral Aldehydes with the tol‐binap/dbapen/Ruthenium(II) Catalyst

Abstract

Efficient isomerization: The title reaction was catalyzed by the [RuCl2{(S)-tol-binap}{(R)-dbapen}]/KOH system in ethanol at 25 °C (see scheme). A series of E- and Z-configured aromatic and aliphatic allylic alcohols, including a simple primary alkyl-substituted compound (E)-3-methyl-2-hepten-1-ol, were transformed into the chiral aldehydes with at least 99 % ee. dbapen = 2-dibutylamino-1-phenylethylamine, tol-binap = 2,2'-bis(di-4-tolylphosphanyl)-1,1'-binaphthyl.

Microwave versus Conventional Light Activation of O‐Radical Scission Processes

“…The first studies were dedicated to the scission of O radicals derived from terpenes. Inexpensive (–)‐menthol ( 4 ; Scheme ) was used as substrate, because its fragmentation would likely afford the valuable aldehyde ( R )‐(+)‐citronellal ( 5 ) …”

“…( R )‐Citronellal (5): Table , Entry 1: A solution of (–)‐menthol ( 4 ; 32 mg, 0.2 mmol) in dry dichloromethane (3 mL) was treated according to Method A during 150 min. After the usual workup, the residue was dissolved in dry CH 2 Cl 2 (2 mL), and DBU (0.02 mL) was added.…”

“…After the usual workup, the residue was dissolved in dry CH 2 Cl 2 (2 mL) and treated with DBU (0.02 mL) according to the previous procedure. After workup and product purification, ( R )‐citronellal ( 5 ; 17 mg, 55 %) was obtained …”

Iridium‐Catalyzed Asymmetric Isomerization of Primary Allylic Alcohols Using MaxPHOX Ligands: Experimental and Theoretical Study

“…[5a,6] However, several drawbacks have prevented the widespread use of this method: limited reaction scope, high catalyst loadings or elevated temperatures, long reaction times and poor catalyst accessibility. During recent decades, many transition metals have been used, but ruthenium, [7] rhodium [8] and iridium [4b,9] complexes dominate the field in the enantioselective version.…”

Asymmetric synthesis of γ-branched amines via rhodium-catalyzed reductive amination

“…However, varying substituents at the newly introduced stereocenters, such as aryl vs. alkyl, acyclic vs. cyclic, or carbon atom vs. heteroatom, often requires different metal/ligand scaffolds to achieve high enantioselectivity 12 – 14 . The redox neutral isomerization of allylic amines 15 , 16 or alcohols 17 – 19 provides a solution to this problem; however, current methods suffer from very limited substrate scope 9 – 13 . To the best of our knowledge, there is only one reported method for the direct synthesis of chiral γ-branched amines (Fig.…”