Chiral Rhodium Research Articles

Enantioselective Hydrogenation of β‐Acylamino Acrylates Catalyzed by Rhodium(I)‐Monophosphite Complexes

AbstractChiral rhodium(I) complexes bearing monophosphite ligands, prepared from chiral Binol and (L)‐menthol, were found to be efficient catalysts for the asymmetric hydrogenation of β‐acylamino acrylates with ee values up to 94%.

(-)-(9R,10S)-10-Acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene: Optical Resolution, Catalyst Systems, Derivatives and Olfactory Properties

By separation of the enantiomers of the woody-ambery odorant 10-acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene (rac-12) via their diastereomeric (-)-camphanoates, the (-)-(9R,10S)-isomer (9R,10S)-12 was determined to bethe most powerful enantiomer. With an odor threshold of 0.19 ng/L it is about one hundred times stronger than its antipode. Racemic 10-acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene (rac-12) was synthesized by an unusual [4+2]-cycloaddition of 4-methylenespiro[2.7]decane (10) and 3-methylbut-3-en-2-one (11) in the presence of Wilkinson's catalyst. However, attempts to induce optical activity with chiral rhodium(I) catalysts proved futile. Platinum(II)-DIOP catalysts furnished traces (0.05% GC yield) of (-)-(9R,10S)-10-acetyl-9,10-dimethylbicyclo[6.4.0]dodec-1(8)-ene [(9R,10S)-12] with an enantiomeric excess of around 40% ee. For further studies on the structure-odor correlation of woody odorants, two new tricyclic analogs of rac-12, (′)-(2R*,3S*,7S*)-2-methyltricyclo[7.6.0.0 3 . 7 ]pentadec-1(9)-en-4-one (18) and (′)-(2R*,3S*,7S*)-2,3-dimethyl-tricyclo[7.6.0.0 3 , 7 ]pentadec-1(9)-en-4-one (20) were synthesized and characterized.

New insights on the asymmetric hydroboration of perfluoroalkenes.

Enantioselective access to Markovnikov regioisomeric perfluoroalcohols is achieved in the presence of chiral cationic rhodium complexes and specific hydroborating reagents.

Allylation of aldehydes catalyzed by chiral N,N'-bis(N-methyl-2-methylene-4,5-bisphenyl-imidazole)-1,2-cyclohexane diamine rhodium(III) complexes

Chiral bis-imidazole rhodium(III) complexes catalyze the allylation of aldehydes by allyltributyltin. The pre-catalyst was readily prepared from chiral N,N'-bis(N-methyl-2-methylene-4,5-bisphenylimidazole)-1,2-cyclohexanediamine, potassium carbonate, and rhodium(III) chloride trihydrate. The rhodium(III) complex produced showed no activity in an allyl transfer process in the presence of the allyltin reagent. However, when silver tetrafluoroborate was added to the pre-catalyst and stirred for 1 h, the resulting system became an efficient catalyst for the allyl transfer process. The reductions produced homo-allyl alcohols with good to excellent yield, although generally with poor facial selectivity (8–10% ee, aryl aldehydes, 4 examples; 99% ee, aliphatic aldehyde, 1 example).Key words: allylation, aldehydes, enantioselectivity, rhodium(III) tetramine complex.

Chiral Rhodium(II,II) Dimers Catalyzed Enantioselective Intramolecular Aziridination of Sulfonamides and Carbamates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic Hydrogenation of Acetophenone with Hydrogen Transfer over Chiral Diamine Rhodium(I) Complexes

The catalytic activity and stereoselectivity of Rh(I) complexes with C 2-symmetric chiral diamines, (4S,5S)-3,4-isopropylidenedioxy-1,4-butanediamine and (4S,5S)-N,N,N',N'-tetramethyl-3,4-isopropylidenedioxy-1,4-butanediamine [skeletal analogs of 2,3-dihydroxy-2,3-O-isopropylidene-1,4-bis(diphenylphosphino)butane (DIOP)], were studied in hydrogen transfer from 2-propanol to acetophenone in the presence of KOH or t-BuOK. The product, (S)-(-)-2-phenylethanol, was thus obtained with an optical yield of 67%. Covalent chloride rhodium complexes with the above ligands give rise to the same stereoisomer, whereas the opposite stereoselectivity is observed under catalysis by cationic trifluoromethanesulfonate rhodium(I) complexes. X-Ray phase analysis showed formation of nanosize particles in the precipitate of metallic rhodium.

A Tandem Metal Carbene Cyclization—Cycloaddition Approach to the Pseudolaric Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Selectivity in Rhodium(II) Catalyzed Reactions of Diazo Compounds: Effects of Catalyst Electrophilicity, Diazo Substitution, and Substrate Substitution. From Chemoselectivity to Enantioselectivity

AbstractFor Abstract see ChemInform Abstract in Full Text.

Efficiency of natural bentonite versus synthetic organo(bis-silantriolates) as supports towards the heterogenisation of asymmetric hydroboration

Ionic chiral rhodium complexes can be separated, recovered and reused between consecutive asymmetric catalytic hydroboration reactions of vinylarenes, more efficiently when they are immobilised by electrostatic attraction on clay bentonite than on organo(bis-silantriolates).

Asymmetric 1,4‐Addition of Organosiloxanes to α,β‐Unsaturated Carbonyl Compounds Catalyzed by a Chiral Rhodium Complex.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A tandem metal carbene cyclization-cycloaddition approach to the pseudolaric acids.

An approach toward the synthesis of the antifungal and cytotoxic pseudolaric acids based on the tandem metal carbene cyclization-cycloaddition reaction is described. Using this strategy, the advanced intermediate 3a bearing three of the four stereocenters of the target molecules has been synthesized. The substrate-controlled diastereoselectivity of the tandem carbene cyclization-cycloaddition was preferential for the undesired diastereomer, but reagent control through the use of Hashimoto's chiral rhodium catalyst Rh(2)(S-BPTV)(4) reversed the selectivity in favor of 3a. Ring opening of the oxabicyclic nucleus to give a hydroxycycloheptene has been demonstrated in a model study.

Practical Synthesis of Optically Active Styrene Oxides via Reductive Transformation of 2‐Chloroacetophenones with Chiral Rhodium Catalysts.

A practical method for the synthesis of optically active styrene oxides has been developed via formation of optically active 2-chloro-1-phenylethanols generated by reductive transformation of ring-substituted 2-chloroacetophenones. The optically active alcohols with up to 98% ee are obtainable from the asymmetric reduction of acetophenones with an S/C = 1000−5000 with a formic acid triethylamine mixture containing a well-defined chiral Rh complex, Cp*RhCl[(R,R)-Tsdpen].

Asymmetric Hydrogenation of Enamides in Aqueous Media with a New Water‐Soluble Chiral Rhodium‐α,α‐trehalose‐Derived Phosphine—Phosphinite Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective Hydrogenation of Enamides Catalyzed by Chiral Rhodium—Monodentate Phosphite Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Rh(I)-Catalyzed Asymmetric Intramolecular Pauson-Khand Reaction in Aqueous Media

The first rhodium-BINAP complex-catalyzed enantioselective Pauson-Khand reaction in aqueous media, which is accelerated by surfactant, is reported. The chiral rhodium catalyst is easily prepared in situ from I equivalent of [Rh(cod)Cl] 2 and 2 equivalents of BINAP under I atm of CO and a temperature of 60 °C or 90 °C. Ee's up to 96% were achieved for the intramolecular Pauson-Khand reaction, but the yields are highly dependent upon the substrate itself.

Iridium‐Catalyzed Enantioselective Hydrogenation of Olefins

AbstractCationic iridium complexes with chiral P,N‐ligands and tetrakis[3,5‐(trifluoromethyl)phenyl]borate (BArF) as the counterion are efficient homogeneous catalysts for the enantioselective hydrogenation of olefins. The complexes are readily prepared, air‐stable, and easy to handle. In contrast to chiral rhodium‐ and ruthenium‐phosphine catalysts, they do not require the presence of a polar coordinating group near the CC bond. In the hydrogenation of unfunctionalized arylolefins, high enantioselectivities of >95% ee with turnover numbers of up to 5000 and turnover frequencies of >5000 h−1 have been achieved.

A New Atropisomeric P,N Ligand for Rhodium‐Catalyzed Asymmetric Hydroboration.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds catalyzed by a chiral rhodium complex.

Highly enantioselective 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds was found to be catalyzed by a chiral rhodium complex generated from [Rh(cod)(MeCN)(2)]BF(4) and (S)-BINAP. Both (E)- and (Z)-1-alkenyl groups as well as aryl groups can be introduced enantioselectively into the beta-position of a variety of ketones, esters, and amides. [reaction--see text]

Practical synthesis of optically active styrene oxides via reductive transformation of 2-chloroacetophenones with chiral rhodium catalysts.

[reaction: see text] A practical method for the synthesis of optically active styrene oxides has been developed via formation of optically active 2-chloro-1-phenylethanols generated by reductive transformation of ring-substituted 2-chloroacetophenones. The optically active alcohols with up to 98% ee are obtainable from the asymmetric reduction of acetophenones with an S/C = 1000-5000 with a formic acid triethylamine mixture containing a well-defined chiral Rh complex, CpRhCl[(R,R)-Tsdpen].

Asymmetric hydrogenation of enamides in aqueous media with a new water-soluble chiral rhodium-α,α-trehalose-derived phosphine–phosphinite catalyst

A new chiral rhodium catalyst with α,α-trehalose-derived phosphine–phosphinite (α,α-TREHAPPN) ligand, [(TREHAPPN)Rh(cod)]BF 4 8 has been prepared. This catalyst is soluble in water and is an effective chiral catalyst for asymmetric hydrogenation of N-acyldehydroamino acids in aqueous media to give enantiomerically enriched α-amino acid derivatives with R configuration. The simple decantation allows retrieval of the catalyst from the reaction mixture, the recovered catalyst being re-used without marked loss of enantioselectivity.