Ulrich Nagel

The enantioselective hydrogenation of N-acyl dehydroamino acids

The historical development of asymmetric hydrogenation of N-acyl dehydroamino acids and their derivatives is reported. Both homogeneous and heterogeneous catalysis are illustrated by selected examples. Catalysis by water soluble complexes and transfer hydrogenation are also treated in this review. The mechanism of catalytic hydrogenation, its elementary steps and the origin of enantioselection are discussed.

Metallorganische Lewis-Sa¨uren: XXXIV. Kationische Pentacarbonyl(isocyanid)rhenium(I)-Komplexe und deren Reaktionen mit Nucleophilen

Abstract Pentacarbonyl(tetrafluoroborato)rhenium, (OC)5ReFBF3, reacts with isocyanides to give the ionic complexes [(OC)5ReCNR]+BF4− (1) (R = CMe3, C6H11, Ph, CH2CO2Et, CH2SO2C6H4Me). The reactivity of 1 with nucleophiles (N3−, OH−, OR−, NH2R, NHR2) has been studied. In complexes 1 with R = CMe3, C6H11, Ph, nucleophilic attack occurs at the carbon monoxide ligand to give the compoundscis-(OC)4Re(CNR)NCO (R = CMe3, Ph), cis-(OC)4Re(CNR)COOH (R = CMe3, C6H11), cis-(OC)4Re(CNCMe3)CO2R′ (R′ = Me, Et), cis-(OC)4Re-(CNCMe3)CONHR′ (R′ = CH2Ph, (CH2)3OH), cis-(OC)4Re(CNCMe3)CONR2′ (2R′ = (CH2)4), respectively. Reaction of 1 with ethylene diamine, 1, 6-diaminohexane or piperazine gives the dicarbamoyl-bridged complexes Me3CNC(OC)4ReCONH(CH2)nNHCORe(CO)4CNCMe3 (n = 2, 6) and Me3CNC(OC)4ReCON(CH2CH2)2NCORe(CO)4CNCMe3. In complexes 1 (R = CH2CO2Et, CH2SO2C6H4Me) hydroxide adds to the carbon atom of the isocyanide ligand to yield the pentacarbonylcarbamoyl complexes, (OC)5ReCONHR.

Metallorganische Lewis-Säuren, XIV [1]. Ethylen-verbrückte Mangan- und Rheniumcarbonyle; Tieftemperatur-Röntgenstrukturanalyse von (OC)5ReCH2CH2Re(CO)5 / Organometallic Lewis Acids, XIV [1]. Ethylene Bridged Manganese and Rhenium Carbonyls; Low Temperature X-Ray Structure of (OC)5ReCH2CH2Re(CO)5

Abstract The tetrafluoroborato complexes (OC)5MFBF3 (M = Mn, Re) which are obtained by methyl abstraction from (OC)5MCH3 using Ph3CBF4 react with ethylene or propene at room temperature and 1 bar to give [(OC)5M(alkene)]+ BF4-. By nucleophilic addition of the carbonylmetalates [M(CO)s] -(M = Mn, Re) to the coordinated alkene in these cationic complexes [(OC)5M(alkene)]+ the alkene bridged complexes (OC)5MCH2CH(R)M(CO)5 (M = Mn, Re; R = H, Me) are formed. Also the mixed-metal complex (OC)5MnCH2CH2Re(CO)5 has been isolated. According to an X-ray structure at low temperature (OC)5ReCH2CH2Re(CO)5 can be considered as a dimetal substituted ethane with a carbon-carbon distance of 152 pm.

Reactions of β-lactones with Lewis acids: Ring enlargement versus β-elimination

Abstract On treatment with MgBr2 the β-spirolactones 7 and 10 undergo ring enlargement to the γ-lactones 8 and 11, whereas the β-spirolactones 13 show diastereoselective β-elimination to form the β,γ-unsaturated acids 14. The Lewis acid influence on the migratory aptitude of Me versus H is studied for β-lactone 18.

Enantioselective catalysis XVI: regio- and enantioselectivity in nickel-catalysed cross-coupling reactions of allylic substrates with Grignard reagents☆

Abstract An investigation of the asymmetric synthesis of 3-phenyl-1-butene by the cross-coupling reaction of linear 2-butene-1-yl compounds and of branched 1-butene-3-yl substrates with phenylmagnesium halides is presented. Nickel and palladium complexes bearing chiral 3,4-bis(phosphanyl)pyrrolidine or 3-(diphenylphosphanyl)pyrrolidine ligands have been employed as catalysts. The quantitative analysis and the determination of enantiomeric composition of the catalytic samples were accomplished using enantioselective gas-liquid chromatography separations. Regio- and enantioselectivity can be influenced by the choice of the leaving group present in the allylic substrates and additionally by the choice of the ligand to nickel ratio in the case of monophosphane ligands. The influence of tertiary phosphanyl groups in three 3,4-bis(phosphanyl)pyrrolidine ligands, differing in basicity and molecular volume on chemical yield and on regio- and enantioselectivity is investigated. High chemical and optical yields (up to 83.5% ee) can be exclusively obtained with 3,4-bis(diphenylphosphanyl)pyrrolidine ligands. This conclusion contrasts with the results of another cross-coupling reaction yielding 3-phenyl-1-butene ((1-phenylethyl)magnesium halides and vinyl halides as starting compounds). In this catalysis nickel complexes bearing 3-(diphenylphosphanyl) pyrrolidine ligands were the most enantioselective catalysts.

Enantioselective Catalysis, XVII [1]. Enantioselective Catalytic Hydrogenation of Unfunctionalized Ketones

Abstract Three diastereomeric rhodium bisphosphane complexes have been applied to asymmetric hydrogenation of unfunctionalized, non-chelating aliphatic and aromatic ketones. The ee values of the catalysis products differ considerably for the diastereomerical catalysts. 70% ee were obtained in hydrogenating butyrophenone, and 83.7% ee for pinacoline. The results depend strongly on the solvent used.

Stable Oxapenem-3-carboxylic Acids – A New Class of β-Lactam Antibiotics. Influence of 2- and 6-Alkyl Substituents

Novel antibacterially active oxapenem-carboxylic acids were prepared. Their increased stability depends on the 2-tert-butyl substituent and arises from its electron releasing inductive effect. The geometry and reactivity of oxapenems are discussed on the basis of two X-ray structure determinations and compared to those of related antibiotics.

Metallkomplexe mit biologisch wichtigen Liganden, XL [1]. Iridium(III)-Komplexe mit 9-Methylguanin / Metal Complexes with Biologically Important Ligands, XL [1]. Iridium(III) Complexes with 9-Methylguanine

The dinitrogen-tetrafluoroborato complex (Ph3P)2(Cl)(N2)(H)IrFBF3 reacts with 9-m ethylguanine in CH2Cl2 to give [(Ph3P)2(Cl)(H)Ir(9-methylguanine)]+BF4- (2). From a solution of 2 in methanol the complex (Ph3P)2(Cl)2(H)Ir(9-methylguanine) (3) is obtained. The reaction of [(Ph3P)2(Cl)(N2)(H)IrOSO2C4F9] with 9-methylguanine affords the com plexes [(Ph3P)2(Cl)(N2)(H)Ir(9-methylguanine)]+C4F9SO3- (5) and [(Ph3P)2(Cl)(H2O)(H)Ir(9-methylguanine)]+ C4F9SO3- (6). The coordination of the guanine derivative to the iridium atom in 2, 5, 6 is discussed on the basis of the infrared spectra. The crystal structure of 3 was determined. 9-Methylguanine is coordinated via N (7). Intermolecular hydrogen bonding between the chloro-ligand and HN (1) of guanine leads to linear chains in the crystal.

Enantioselektive Katalyse, XVIII Der Einfluß nicht koordinierter Stereozentren auf die enantioselektive Hydrierung/Enantioselective Catalysis, XVIII The Influence of Non-Coordinated Stereocenters on the Enantioselective Hydrogenation

Abstract 3,4-Bis{[2-(methyl-phenyl-oxophosphanyl)-ethyl]phenyl-phosphanyl}pyrrolidines have been synthesized by Michael Addition from the corresponding methyl-phenyl-vinyl-phosphane oxides and 3,4-bis(phenylphosphino)pyrrolidines. For purification of the ligands palladium complexes were used and with the enantiomerically pure ligands Rh complexes have been prepared. The catalyst has 6 stereogenic centers. In the hydrogenation of Z-α-acetamidocinnamic acid all six stereogenic centers have an influence on the enantioselectivity. The influence is strongest from the C stereocenters of the pyrrolidine ring. Less important are the stereogenic centers on the coordinated P atoms. The influence of the stereocenters on the non-coordinated P = O groups is the least, but it is not negligible. The ee values obtained with the ligands containing P = O groups are much lower than those obtained with ligands which are substituted only with aryl groups. Ketones are hydrogenated with only low ee’s.

Metallkomplexe mit biologisch wichtigen Liganden, XLVIII [1]. Palladium(II)- und Platin(II)-Komplexe mit α,β-Dehydro- und β-Chlor-α-aminosäurederivaten sowie mit O-Acetyl-L-serin / Metal Complexes with Biologically Important Ligands, XLVIII [1] Palladium(II)- and Platinum(II)-Complexes of α,β-Dehydro- and β-Chloro-α-amino Acid Derivatives and of O-Acetyl-L-serine

The preparation and spectroscopic data of the complexes cis- and trans- CL2M(NH2C(CO2Et)=C<) , (1) (M - Pd. Pt), trans-Cl2Pd(NH2CH(CH2Cl)CO2CH3)2 (2), trans- Cl2Pd(NH2CH(CH2OAc)CO2)2 (3) and trans-Cl2Pt(Gly-β-Cl-AlaOMe)2 (4) are reported. The structures of l a and 2 have been determined by X-ray structure analysis. Elimination of hydrogen chloride from 4 gives the dehydrodipeptide complex 5.