Structural requirements in chiral diphosphine-rhodium complexes—XII: Asymmetric homogeneous hydrogenation of Z-α-N-methylacetamidocinnamic acid and methyl ester catalyzed by rhodium(I) complexes of DIOP and its carbocyclic analogues

Z-α-N-methylacetamidocinnamic acid and its methyl ester were hydrogenated with rhodhim(I) complexes containing (2R, 3R)-O-2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane (DIOP) or its carbocyclic analogues: (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane or (1S,2S)-trans-1,2-bis(diphenylphosphinomethyl) cyclohexane. The N-acetyl-N-methylphenylalanine methyl ester reaction product was formed with an optical purity of 73% ee-(R) [(2R, 3R)-DIOP]; 43% ee-(R) [(1R, 2R)-cyclobutane analogue]; and 26% ee-(R) [(1S,2S])-cyclohexane analogue]. Similarly, N-acetyl-N-methylphenylalanine was formed with an optical purity of 87% ee-R [(2R, 3R)-DIOP] and 68% ee-(R) [(1R, 2R)-cyclobutane analogue].     

Structural requirements in chiral diphosphine-rhodium complexes. X asymmetric homogeneous hydrogenation of z-N-acetyldehydroamino acids and esters with (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane/rhodium(I) complexes.

Z--acetamidocinnamate esters were hydrogenated with neutral rhodium(I) complexes containing (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane. Increasing the steric bulk of the alcohol moiety in the unsaturated esters had little influence upon the optical purity of the N-acetylphanylalanine ester products. In the series Me, Et, i-Pr, and t-Bu the optical purity decreased from 44 % ee-(R) [Me] to 40 % ee-(R) [t-Bu]. The chiral cyclobutane diphosphine appears to be only slightly more effective than the heterocyclic DIOP when ring-substituted Z--acetamidocinnamic acids are hydrogenated with neutral rhodium(I) complexes without the addition of triethylamine. Addition of triethylamine to the solvent blend seems to be more beneficial to the cyclobutane analogue than to DIOP.     

Structural requirements in chiral diphosphine-rhodium complexes—XIII: Steric and electronic factors in the asymmetric homogeneous hydrogenation of Z-α-acylaminocinnamic acids and esters catalyzed by rhodium(I) complexes

Z-α-acylaminocinnamic acids and esters were hydrogenated with rhodium(I) complexes containing (4R,5R) - trans - 4,5 - bis(diphenylphosphinomethyl) - 2,2 - dimethyl - 1,3 - dioxolan (DIOP). Increasing the steric bulk of the acyl function (NHCOR, where R is an alkyl moiety) resulted in a lowered reduction of the si-re prochiral face to yield a decreasing excess of the (R)-amino acid derivatives. In the series of N-acylphenylalanine free acids (resulting from hydrogenation of Z-α-acylaminocinnamic acids) the optical purity decreased from 82% ee-(R) [Me]; 57% ee-(R) [i-Pr]; 52% ee-(R) [t-Bu]; to 46% ee-(R) [1-adamantyl]. Theα-benzamido, α-formamido and α-trifluoroacetamido substrates gave hydrogenation products having 68% ee-(R) [Ph]; 60% ee-(R) [H]; and 16% ee-(R)[CF₃]. In the corresponding methyl esters, increasing the steric bulk of the acyl function (NHCOR) resulted in a markedly greater decrease in enantioface differentiation. In the series of N-acylphenylalanine methyl ester products (resulting from hydrogenation of Z-methyl α-acylaminocinnamates) the optical purity decreased from 69% ee-(R)[Me]; 15% ee-(R) [i-Pr]; to 0% ee[t-Bu and 1-adamantyl]. The α-benzamido, α-formamido, and α-trifluoroacetamido substrates gave hydrogenation products having 36% ee-(R) [Ph]; 58% ee-(R) [H]; and 22% ee-(S) [CF₃]In the series of N-acetylphenylalanine alkyl ester products (resulting from hydrogenation of Z-alkyl α-acetamidocinnamate esters) trifluoro substitution in the alkyl alcohol moiety resulted in a decrease in optical purity to 52% ee-(R) [CH₂CF₃] compared to 72, 76 and 77% ee-(R) [Et, i-Pr and t-Bu, respectively].     

Structural requirements in chiral diphosphine-rhodium complexes—XI: Asymmetric homogeneous hydrogenation of z-α-acylaminocinnamic acids and esters with (1s, 2s)-trans-1,2-bis(diphenylphosphinomethyl) cyclohexane/rhodium(i) complexes

Z-α-acylaminocinnamate esters were hydrogenated with neutral rhodium(I) complexes containing (1S, 2S)-trans-1,2-bis(diphenylphosphinomethyl)cyclohexane. Increasing the steric bulk of the alcohol moiety of the ester function results in increased enantioface differentiation in favor of the re-si prochiral face to yield an excess of the S-amino acid derivatives. In the series of N-acetylphenylalanine ester products (resulting from hydrogenation of Z-α-acetamidocinnamate esters) the optical purity increased from 1% ee-(R) [Me]; 20% ee-(S) [Et]; 47% ee-(S) [i-Pr]; to 58% ee-(S) [t-Bu]. Increasing the steric bulk of the acyl function (NHCOR, where R is an alkyl moiety) favors the reduction of the si-re prochiral face [in the methyl ester substrates] to yield an excess of the R-amino acid derivatives. In the series of N-acylphenylalanine methyl ester products (resulting from hydrogenation of Z-methyl α-acylaminocinnamates) the optical purity increased from 1% ee-(R) [Me]; 13% ee-(R) [i-Pr]; to 15% ee-(R) [t-Bu and 1-adamantyl]. The α-formamido and α-benzamido substrates gave hydrogenation products having 22% ee-(R) [H] and 35% ee-(R) [Ph]. In the corresponding free acids, increasing the steric bulk of the acyl function (NHCOR, where R is an alkyl moiety) results in almost no change in the optical purity of the reduction products. In the series of N-acylphenyl-alanine products (resulting from hydrogenation of Z-α-acylaminocinnamic acids) the optical purity was 35% ee-(S) [Me]; 31% ee-(S) [i-Pr]; 33% ee-(S) [t-Bu]; and 35% ee-(S) [1-adamantyl]. The α-benzamido substrate gave a hydrogenation product having 8% ee-(S).     

Asymmetric hydrogenation using ferrocenylphosphine rhodium(I) cationic complexes

High optical yields are obtained in the hydrogenation of α-acetamidocinnamic acid using [(COD)Rh((+)PPFA)]ClO₄ and related complexes as catalysts. (+)PPFA is (S)-α-[(R)-2-diphenylphosphinoferrocenyl] ethyldimethylamine.     

Structural requirements in chiral diphosphine-rhodium complexes. VII. Use of Z-methyl-α-acylaminocinnamtes as structural probes for Diop-rhodium(I) complexes.

(+)-(25,3S)-DIOP was used in neutral rhodium(I)-diphosphime complexes to catalyze the asymmetric hydrogenation of Z-methyl-u-acylaminocimnamates. Increasing steric bulk in the acyl function (NHCOR, where R is a hydrocarbon moiety) resulted in a decrease in optical purity of the N-acylphenylalanine methyl ester products. The optical purity decreased from 69 % ee (S) [Me], 15 % ee (S) [i-Pr], to 0 % ee [t-Bu and 1-adamantyl]. The α-formamido substrate decreased in optical purity [58 % ee (S)] relative to the Me analogue. The a-trifluoroacetamido analogue gave a reversal in chirality [22 % ee (R)].     

New chiral diphosphoramidite rhodium(I) complexes for asymmetric hydrogenation

Chiral 1,5‐cyclooctadiene rhodium(I) cationic complexes with C₂‐symmetric chelate diphosphoramidite ligands containing (R,R)‐1,2‐diaminocyclohexane as the backbone and two atropoisomeric biaryl units were easily synthesized and fully characterized by multinuclear one‐ and two‐dimensional NMR spectroscopy and elemental analysis. These complexes were used as catalysts in the asymmetric hydrogenation of dimethyl itaconate, methyl 2‐acetamidoacrylate and (Z)‐methyl‐2‐acetamido‐3‐phenylacrylate. The rhodium complexes derived from diphosphoramidite ligands that contain two (R) or (S) BINOL (2,2′‐dihydroxy‐1,1′‐binaphthyl) units proved to be efficient catalysts, giving complete conversion and very good enantioselectivity (up to 88% ee). An uncommon positive H₂ pressure effect on the enantioselectivity was observed in the hydrogenation of dimethyl itaconate catalyzed by Rh‐complex with diphosphoramidite ligand that contains two (S)‐binaphthol moieties. Copyright © 2014 John Wiley & Sons, Ltd.     

Asymmetric hydrogenation of alkenes with planar chiral 2-phosphino-1-aminoferrocene-iridium(I) complexes

The first highly enantioenriched and enantiopure planar chiral 2-phosphino-1-aminoferrocene ligands and their Ir(COD)BAr_F complexes are reported. The ligands display bidentate coordination behavior towards iridium, as indicated by trends in ³¹P and ¹H NMR spectra of the phosphine moieties and the α to nitrogen substituents of the amines. All of the new complexes showed good reactivity as catalysts in promoting asymmetric hydrogenation of several prochiral alkenes, with enantioselectivities up to 92%. Iridium complexes of dimethylaminoferrocene derivatives containing P-Ar groups [PPh₂ and P(o-tol)₂] gave the highest levels of asymmetric induction.     

Asymmetric catalysis. Part 128: Diastereomeric rhodium(I) complexes in the enantioselective hydrogenation of ketopantolactone

In the hydrogenation of ketopantolactone, new rhodium complexes bearing (R,R)-diop and various bidentate chiral N,N′ co-ligands with (R)- or (S)-configuration were used. On the one hand, the N,N′ co-ligands consist of pyrroleimines, which derive from (R)- and (S)-1-phenylethylamine, (R)- and (S)-1-cyclohexylethylamine (and benzylamine), and on the other hand of pyrroleoxazolines and pyridineimines. Stereoselectivities of 31–33% ee for (R)-pantolactone were achieved using related compounds (RR-R) and (RR-S), respectively, with no double stereoselectivity being observed. It is assumed that during catalysis the pyrroleimines bind in a monodentate way at the sixth coordination site of the rhodium atom by the pyrrole nitrogen with the imine nitrogen carrying the different chiral substituents far away from the rhodium atom. Monodentate deltacyclane phosphanes, chloro ligands or solvent molecules, bound at the sixth coordination site of the catalyst, led to widely differing enantioselectivities in the ketopantolactone hydrogenation.     

Asymmetric hydrogenation of activated keto compounds catalyzed by new chiral peralkyl-ampp rhodium complexes

Readily available peralkyl aminophosphinephosphinite ligands (alkyl-AMPP) give neutral rhodium complexes active for the catalytic reduction of some activated ketones under atmospheric hydrogen pressure at ambient temperature (ee = 80 %).     

Asymmetric synthesis of dipeptides by means of homogeneous hydrogenation catalyzed by chiral rhodium complexes

Asymmetric hydrogenation of dehydrodipeptides, α-acylaminocinnamoyl-(S)-amino esters, catalyzed by rhodium complexes with chiral diphosphines gave either (R)-N-acylphenylalanyl-(S)-amino esters or (S)-N-acylphenylalanyl-(S)-amino esters with high diastereomeric purity up to 98–99% on using proper chiral ligands.     

Asymmetric epoxidation by chiral ketones derived from carbocyclic analogues of fructose.

A number of carbocyclic analogues of the fructose-derived ketone 1 have been prepared and investigated for asymmetric epoxidation. The studies show that the oxygen atom of the pyranose ring of 1 has an impact on the catalyst's activity and selectivity. Conformational, electronic, and steric effects are discussed.     

Asymmetric transfer hydrogenation of ketones catalyzed by rhodium and iridium complexes with chiral bidentate Schiff's bases

Rhodium and iridium complexes of Schiff's bases derived from (1R,2R)- and (1S,2S)-diaminocyclohexane catalyze asymmetric transfer hydrogenation of alkyl aryl ketones in PrⁱOH at room temperature to give chiral secondary alcohols (up to 65% ee).     

Chiroptical properties and enantioselectivity in hydrogenation with rhodium(I) complexes of chiral bis-diphenylphosphines derived from -glucose and -galactose

(2R,3S)-2-Diphenylphosphinomethyl-3-diphenylphosphinotetrahydropyran (3) has been prepared in 64% yield from the dimesylate 5, derived from -galactose. The surprisingly different reactivities of dimesylates 2 and 5 towards diphenylphosphide anion are considered and the conformational properties of 1–6 discussed in terms of their CD spectra. The rhodium(I) complexes 9 and 10 exhibit low to relatively high enantioselectivities in hydrogenation of Z-α-acetylaminocinnamic acid and α-acetylaminoacrylic acid. The chiroptical and conformational properties of the bidentate ligands (3, 6), and their rhodium(I) complexes (9, 10) are correlated with the observed enantioselectivities.