Catalytic Asymmetric Isomerization of (Homo)Allylic Alcohols: Recent Advances and Challenges

Abstract

Catalytic asymmetric isomerization of allylic or homoallylic alcohols into synthetically useful carbonyl compounds is a redox‐neutral and 100 % atom‐economic transformation, which is of great interest and has gained increasing attention from both academic and industry. This minireview summarizes the advances in catalytic enantioselective isomerization and it involved tandem reactions over the past five years, also discusses their advantages and limitations, and expounds the synthetic chances still open for further development.

Ru complexes containingN‐methyl‐1,3,5‐triaza‐7‐phosphaadamantane (mPTA) as catalysts for the isomerization of 2‐cyclohexen‐1‐ol

“…An adequate catalyst should isomerize the allylic alcohols under mild reaction conditions and in non‐harmful solvents such as water. [ 18 ] Complexes containing Ni, Pd, Os, Ir, Ru, Rh, and Mo were found to be catalysts for the isomerization of allylic alcohols, [ 19,20 ] but ruthenium‐based compounds are among the most used and studied due to the fact that Ru presents several important features: a wide range of available oxidation states, a great coordination versatility, and is cheaper than other noble metals such as Ir or Rh. Hydrosoluble ruthenium complexes that showed to be excellent catalysts for many reactions in water [ 21‐27 ] commonly contain hydrophilic tertiary organophosphines, [ 28 ] N‐heterocyclic carbenes, [ 29 ] and tetrahydrosulfosalan or tetrahydrosulfosalene ligands.…”

Iridium-Catalyzed Enantioselective Transfer Hydrogenation of 1,1-Dialkylethenes with Ethanol: Scope and Mechanism

“…The substrate with a benzyl alcohol also proceeded smoothly with 91:9 er at 35 °C ( 38 ). This formally redox-neutral reaction provides a transformation resembling the asymmetric chain-walking isomerization of alkenols . However, the known chain-walking methods give high enantioselectivity only with (homo)­allylic alcohols bearing aryl or carbonyl substituents on the CC double bonds .…”

Synthesis of 1,4-diketones via palladium/photo-cocatalyzed dehydrogenative cross-coupling

“…This result indicates that alcohol 1a and ketone 7 may remain in a HPd( ii )H/Pd(0)-mediated hydrogenation/dehydrogenation equilibrium, wherein hydrogenation of 7 by HPd( ii )H to 8 also occurs. 25 When enone 7 was directly used as the starting material in the reaction without Pd(OAc) 2 , the hydroacylation product was furnished in 84% yield (Scheme 3C). 11 a Notably, enone 7 was not detected in the catalytic reaction under the standard conditions when butanal was present.…”