Regioselective reductions of β,β-disubstituted enones catalyzed by nonracemically ligated copper hydride

CuH-catalyzed 1,2-additions to β,β-disubstituted α,β-unsaturated ketones have been further explored. Asymmetric reductions of enones lacking an α-substituent can be achieved with CuH complexed by DTBM-SEGPHOS in Et₂O at ?25 °C leading to the generation of highly valuable nonracemic allylic alcohols. The corresponding 1,4-reductions can also be achieved using the same reaction conditions by switching the ligand to a JOSIPHOS analog affording nonracemic β,β-disubstituted ketones. DFT calculations of the enone conformations and transition-state energies for model 1,2- and 1,4-additions were carried out to clarify the factors affecting the product ratios.     

Furanoside phosphite–phosphoroamidite and diphosphoroamidite ligands for Cu-catalyzed asymmetric 1,4-addition reactions

A sugar-based phosphite–phosphoroamidite and diphosphoroamidite ligand library L1–L5a–g was tested in the asymmetric Cu-catalyzed 1,4-conjugate addition reactions of β-substituted and β,β′-disubstituted enones. Our results indicated that the selectivity was strongly dependent on the ligand parameters and on the substrate structure. Moderate-to-good enantioselectivities (ees up to 84%) were obtained in the 1,4-addition of several types of β-substituted cyclic and linear substrates. Of particular note is the high enantioselectivity (ees up to 90%) obtained for the more challenging β,β′-disubstituted 3-methyl-cyclohexenone.     

1,4-Additions of electron-rich heterocycles onto β-perfluoroalkyl enones

β-(Trifluoromethyl) enones, easily obtained in few steps from commercially available methyl hemiketal of trifluoroacetaldehyde, react with electron-rich O- and N-containing heterocycles (furans and benzofurans, pyrroles and indoles, hydroxycoumarins), through a 1,4 addition, to give heterocycles bearing a functionalized side-chain. β-(chlorodifluoromethyl)enones and β-(pentafluoroethyl)enones behave in the same way.     

Enantioselective synthesis of 3,4-dihydropyran derivatives via organocatalytic Michael reaction of α,β-unsaturated enones

A simple chiral diamine catalyst (1a) was successfully applied in the asymmetric Michael reaction between cyclic dimedone and α,β-unsaturated ketones. Both acyclic enones with aryl or alkyl β-substituents and cyclic enones were tolerated well in the reaction. The desired adducts were obtained in high yields (up to 98%) with excellent enantioselectivities (up to 97% ee). The additives were found to increase the reactivity dramatically. The biologically active 2,4-disubstituted polyhydroquinoline scaffold was conveniently prepared through an ammoniation from the generated 3,4-dihydropyran product.     

Effect of high pressure on the organocatalytic asymmetric Michael reaction: highly enantioselective synthesis of γ-nitroketones with quaternary stereogenic centers

The significant effect of hydrostatic pressure on the difficult organocatalytic 1,4-conjugate addition of nitroalkanes to prochiral sterically congested β,β-disubstituted enones is demonstrated. This approach allows for the synthesis of γ-nitroketones containing quaternary stereogenic centers with good yields, excellent enantioselectivity, and low loading (1-5 mol %) of simple chiral primary amine catalysts.     

High-pressure accelerated asymmetric organocatalytic Friedel-Crafts alkylation of indoles with enones: application to quaternary stereogenic centers construction

An organocatalytic Friedel-Crafts alkylation of indoles with α,β-unsaturated ketones was found to be efficiently accelerated under high-pressure conditions with a low loading of chiral primary amine salts with good yield and enantioselectivity up to 90%. This approach also allows, for the first time, selected indole derivatives containing quaternary stereogenic centers to be obtained from prochiral β,β-disubstituted enones with an enantioselectivity up to 80%.     

The intramolecular reductive cyclization of cyclic enones

The reductive cyclization (electrohydrocyclization reaction) of tethered cyclic enones has been investigated under electrochemical, metal-mediated, and photochemical conditions. The tricyclic products are generally formed with excellent stereoselectivity, particularly if at least one of the enones is β,β-disubstituted.     

Chelation-Controlled Regioselection in Palladium-Catalyzed Carbonyl Allylation by 4-Pentene-1,3-Diol or Its Cyclic Carbonate

With cat. PdCl₂(PhCN)₂ and SnCl₂, 4-pentene-1,3-diol caused regioselective carbonyl allylation at 3-position in DMF to produce 2-substituted 3-vinyltetrahydrofurans and/or 1-substituted 2-vinylbutane-1,4-diols, and cyclic carbonate of 4-pentene-1,3-diol caused regioselective carbonyl allylation at terminal 5-position in THF to produce 1-substituted 3-hexene-1,6-diols.     

Iron-catalyzed asymmetric epoxidation of β,β-disubstituted enones

The combination of Fe(OTf)(2) and novel phenanthroline ligands enables the catalytic asymmetric epoxidation of acyclic β,β-disubstituted enones, which have been a heretofore inaccessible substrate class. The reaction provides highly enantioenriched α,β-epoxyketones (up to 92% ee) that can be further converted to functionalized β-ketoaldehydes with an all-carbon quaternary center.     

Rhodium-catalyzed asymmetric 1,4-addition of sodium tetraarylborates to β,β-disubstituted α,β-unsaturated esters

A rhodium-catalyzed 1,4-addition of sodium tetraarylborates to β,β-disubstituted α,β-unsaturated esters has been developed. Highly efficient asymmetric catalysis has also been described to create quaternary carbon stereocenters at the β-position of esters by tuning the ester group of substrates and employing a readily available chiral diene ligand.     

Enantioselective 1,4-Addition of Aliphatic Grignard Reagents to Enones Catalyzed by Readily Available Copper(I) thiolates derived from TADDOL. Preliminary communication

Two simple thiols derived from the parent TADDOL, α,α,α′,α′ tetraphenyl-2,2-dimethyl-1,3-clioxolan-4,5-dimethanol, are used to prepare Cu¹ complexes C and D to catalyze (0.05 equiv.) 1,4-additions of Grignard reagents RMgCl to cyclic enones with enantioselectivities which are comparable to or better than previously reported (enantiomer ratios up to 92:8).     

Palladium-catalyzed asymmetric quaternary stereocenter formation

An efficient palladium catalyst is presented for the formation of benzylic quaternary stereocenters by conjugate addition of arylboronic acids to a variety of β,β-disubstituted carbocyclic, heterocyclic, and acyclic enones. The catalyst is readily prepared from PdCl(2), PhBOX, and AgSbF(6), and provides products in up to 99% enantiomeric excess, with good yields. Based on this strategy, (-)-α-cuparenone has been prepared in only two steps.     

Conjugate addition of unactivated thiols to α,β-unsaturated ketones catalyzed by a bifunctional rhenium(V)–oxo complex

ReOCl₃(OPPh₃)(S(CH₃)₂) has been found to be an efficient bifunctional catalyst for the 1,4-addition of thiols to α,β-unsaturated ketones. The addition of thiophenol derivatives and alkyl thiols proceeds under mild reaction conditions without pre-activation of the thiol or exogenous base. Reactions of aryl, alkyl, and cyclic enones produce the corresponding β-sulfanyl ketones in good to excellent yield.     

New synthesis and cyclopropanation of α-phenylselanyl α,β-unsaturated ketones with non-stabilized phosphorus ylides

A general method for the preparation of α-phenylselanyl enones is described. Phosphorus ylides react with these α-phenylselanyl enones in a 1,4-addition, leading to cyclopropanes and/or dihydrofurans, depending on the substitution pattern. This unusual reactivity is due to the phenylselanyl moiety, hindering the carbonyl of the enone and making it less prone to 1,2-additions or promoting conjugate addition by electronic effects.     

Asymmetric Michael addition of malonates to enones catalyzed by a primary β-amino acid and its lithium salt

Highly enantioselective Michael addition of malonates to enones was achieved using a mixed catalyst consisting of a primary β-amino acid, O-TBDPS (S)-β-homoserine, and its lithium salt. Various cyclic and acyclic enones were converted into 1,5-ketoesters in high yields (up to 92%) with high enantioselectivity (up to 97% ee) under mild reaction conditions. Details of synthesis of the catalyst, optimization of the reaction conditions for the Michael addition reaction, and a plausible reaction mechanism are described.     

An atom-economical access to β-heteroarylated ketones from propargylic alcohols via tandem ruthenium/indium catalysis

The direct and chemoselective synthesis of β-heteroarylated ketones from secondary propargyl alcohols through tandem Ru/In catalysis is reported. Both electron-rich and neutral heteroarenes, such as furans and indoles, efficiently undergo the redox isomerization/conjugate addition (RICA) sequence to provide the corresponding adducts in yields of up to 97%.     

Mechanism of the palladium-catalyzed addition of arylboronic acids to enones: a computational study

The palladium(II)-catalyzed addition of arylboronic acids to β,β-disubstituted enones has been investigated with the BP86 density functional. The results show that the mechanism requires three steps: transmetalation, alkene insertion, and protonation. The alkene insertion is the rate-determining step. For unactivated alkenes, the Heck-type β-hydride elimination is more favored than protonation.     

Gold(I)-catalysed arylation of 1,6-enynes: different site reactivity of cyclopropyl gold carbenes

Gold(I)-catalysed addition of electron-rich arenes and heteroarenes to 1,6-enynes gives two different types of products by reaction of the intermediate cyclopropyl gold carbenes at the cyclopropane or at the carbene.     

Amino-sugar modular ligands-useful cores for the formation of asymmetric copper 1,4-addition catalysts

Modular phosphine ligands, synthesised rapidly from commercial N-acetylglucosamine, are very effective in copper(i)-catalysed 1,4-additions of ZnR(2) to linear aliphatic enones (87-95% ee).     

Pyridine stabilized oxiranyl remote anions

The chemistry of oxiranyl remote anions derived from α,β-epoxypyridines is investigated. Deprotonation of α,β-epoxy pyridines at the β-position and reactions of the corresponding anions with a variety of electrophiles are found to be highly regioselective, possibly as a consequence of stabilization from the chelation between lithium and the pyridine moiety in the form of a five-membered cyclic intermediate.