Chiral Rhodium Research Articles

Synthesis of non-proteinogenic (D)- or (L)-amino acids by asymmetric hydrogenation

Non-proteinogenic amino acids play an increasing role in oligopeptide chemistry. Their pharmacological and chemical properties, caused by D-configuration and "unnatural" residues, are more and more used for drug design. Different methods of asymmetric synthesis have been developed during the last decade to prepare "unusual" amino acids. One of them, the asymmetric hydrogenation of dehydroamino aids catalyzed by chiral rhodium (I) complexes, will be described. A series of examples, D- and L-configured, like naphthyl-, thienyl-, furyl-, and pyridylalanines, as well as phenylalanines substituted by chlorine, fluorine, p-nitro, p-methyl, p-trifluoromethyl, p-isopropyl, and p-tert-butyl have been prepared and characterized. Some analytical data like melting points and values of optical rotation are summarized in tables.

Chiral rhodium complexes as catalysts in Diels–Alder reactions

The first rhodium enantioselective catalysts for the Diels–Alder reaction between methacrolein and cyclopentadiene are described; the molecular structure of the catalyst precursor [(η5-C5Me5)Rh(R-Prophos)(H2O)][SbF6]2 is also presented.

Enantioselectivity of the Addition of Singlet and Triplet and the Chiral Rhodium-Complex-Catalyzed Addition of (Methoxycarbonyl)phenylcarbene to 1,3-Dimethylallene

The reactions of enantioenriched 1,3-dimethylallene with singlet and triplet (methoxycarbonyl)phenylcarbene, and with racemic 1,3-dimethylallene in the presence of a chiral rhodium catalyst, have b...

Kinetic Investigations of the Hydrogenation of Diolefin Ligands in Catalyst Precursors for the Asymmetric Reduction of Prochiral Olefins, II[1]

AbstractAsymmetric hydrogenations of prochiral olefines by means of chiral rhodium(I) complexes of the type [Rh(L)(PP*)]A (L = COD, [(Z,Z)‐cycloocta‐1,5‐diene], or NBD (norborna‐2;5‐diene), PP* = chiral bisphosphane forming seven‐membered chelate rings, A = anion like BF4−) are often associated with induction periods caused by partial blocking of the catalyst. NBD complexes are hydrogenated faster than the corresponding COD complexes. Catalytic hydrogenation of COD/NBD mixtures and the determination of the ratio of the Michaelis constants showed that the steady‐state concentration of the COD complex under hydrogen is higher than that of the NBD complex. However, under argon the NBD complex predominates owing to its higher thermodynamic stability compared with that of the COD complex as determined by 31P‐NMR spectoscopy. This complete reversion of the ther‐modynamically determined ratios of COD to NBD complex concentration under hydrogenation conditions was proven by means of UV/Vis spectroscopy.

ChemInform Abstract: Chemoselectivity and Stereoselectivity of Cyclization of α‐ Diazocarbonyls Leading to Oxygen and Sulfur Heterocycles Catalyzed by Chiral Rhodium and Copper Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Homogeneous Catalysis. Mechanism of Diastereoselective Hydroacylation of 3-Substituted-4-pentenals using Chiral Rhodium Catalysts

Homogeneous Catalysis. Mechanism of Diastereoselective Hydroacylation of 3-Substituted-4-pentenals using Chiral Rhodium Catalysts

Construction of α‐phosphonolactams via rhodium (II)‐catalyzed intramolecular CH insertion reactions

AbstractThe Rh(II)‐catalyzed intramolecular CH insertion reactions of N,N‐dialkyl‐α‐diazo‐α‐(diethylphosphono)acetamides 2a,f–j in CHCl3 or ClCH2CH2Cl were found to give monocyclic and bicyclic α‐phosphono‐β‐lactams, 3a and 3f–j, in 43–67% yields via regiospecific α‐CH insertion of the N‐alkyl groups. Similar treatment of N‐benzyl‐N‐isopropyl‐α‐diazo‐α‐(diethylphosphono)acetamide (2b) and the corresponding N‐isobutyl‐N‐methylacetamide 2d in ClCH2CH2Cl afforded mixtures of β‐lactams 3b (35%) and and 3b′ (16%), β‐lactam 3d (47%), and γ‐lactam 4d (10%), respectively, each of which is formed by the competitive CH insertion reaction between benzylic and isopropyl α‐CH bonds and between methyl α‐CH and methine β‐CH bonds, respectively. For the formation of β‐lactams, the selectivity in the rhodium‐mediated CH insertion in ClCH2CH2Cl follows the order methyl > methine > benzylic α‐CH bond on N‐substituents. The N,N‐dibutyl‐α‐diazo homologue 2c and Nα[α‐diazo‐α‐(diethylphosphono)acetyl]‐2‐methylindoline (2k) exclusively produced γ‐lactams 4c (67%) and 4k (81%) via insertion into the methylene β‐CH and methyl β‐CH bonds. tert‐Butyl N‐[α‐diazo‐α‐(dibenzylphosphono)acetyl]‐piperidine‐2‐carboxylate (2m) on similar treatment, followed by deprotection of the benzyl ester afforded the 7‐phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)‐catalyzed cyclization of N‐methyl‐N[4‐benzyloxy‐α‐(diethylphosphono)‐phenyl(diethyl‐phosphono)methyl]‐α‐diazo‐acetamide (2n) led to 1‐[4′‐benzylphenyl(diethylphosphono)methyl] ‐3‐(diethyl‐phosphono)azetidin‐2‐one (3n) in 78% yicld. The phosphono group at C‐7 of 3f was converted into the acetylamino group via a four‐step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b,c produced α‐phosphono‐β‐and γ‐lactams, 3b and 4c, in 6–24% ee and 25–29% ee, respectively.

Kinetische Untersuchungen zur Ligandenhydrierung in Katalysatorvorstufen für die asymmetrische Reduktion prochiraler Olefine

Kinetic Investigations of the Hydrogenation of Ligands in Catalyst Precursors for Asymmetric Reduction of Prochiral OlefinesHerrn Professor Kurt Madeja zum 70. Geburtstag gewidmet. The comparison of chiral rhodium(I) complex catalysts of the type [Rh(L)PP*]A (L = cyclic diolefin; PP* = chiral bis(phosphane) and A = anion like BF) regarding their hydrogenating activity against prochiral substrates is hampered by the induction period in the hydrogen consumption which can be attributed to the formation of the catalytically active species from the diolefin precatalyst. The competing hydrogenation of diolefin [e.g. cis,cis‐cycloocta‐1,5‐diene (COD), norborna‐2,5‐diene (NBD)] and prochiral substrate may cause a maximum of the hydrogenation rate, which is characteristic for different catalyst/substrate/solvent systems. Michaelis‐Menten rate constants for the hydrogenation of COD and NBD were determined for different chiral catalysts by stoichiometric and catalytic hydrogenations. The rate constants differ for one selected diolefin up to a factor of 40. The hydrogenation of NBD is generally 5–8 times faster than the COD hydrogenation. In the special case of precatalysts based on he‐xopyranoside bis(phosphinites) the rate constants for the NBD hydrogenation in comparison with those for COD are higher up to a factor of 48. In some cases the hydrogenation of the mono‐ene is faster than that of the diolefin (e.g. COD, NBD). The high hydrogenation rate reported in the literature for some precatalysts in the asymmetric hydrogenation of prochiral olefins is caused in part by the relatively fast diolefin hydrogenation which facilitates the complete formation of the catalyst. The influence of substrate, solvent, and some experimental conditions on the induction period will be discussed.

Chemoselectivity and stereoselectivity of cyclisation of α-diazocarbonyls leading to oxygen and sulfur heterocycles catalysed by chiral rhodium and copper catalysts

Good levels of enantioselectivity have been achieved in intramolecular C–H insertion reactions of α-diazocarbonyl compounds leading to six-membered oxygen heterocycles (chromanones) through the use of chiral rhodium(II) carboxylates as catalysts. Competition between C–H insertion and sigmatropic rearrangement, the latter leading to five-membered oxygen heterocycles (furanones), was observed with precursors containing a proximal O-allyl side chain. Whereas rhodium carboxylates produced C-H insertion products predominantly, a copper catalyst produced sigmatropic rearrangement products exclusively. A precursor with an S-allyl side chain exhibited cyclisation via sigmatropic rearrangement with both copper and rhodium catalysts.

The first example of enantioselective carbenoid addition to organochalcogen atoms: application to [2,3]sigmatropic rearrangement of allylic chalcogen ylides

In the presence of a catalytic amount of chiral copper(I) or rhodium(II) compounds the enantioselective addition of a carbenoid, derived from ethyl diazoacetate, to chalcogen atoms of aryl cinnamyl chalcogenides affords a diastereoisomeric mixture of ethyl 2-arylchalcogeno-3-phenylpent-4-enoates via[2,3]sigmatropic rearrangement of the intermediate chalcogen ylide with up to 41% ee.

Catalytic asymmetrization of meso-3,7-bis-siloxycycloheptene by chiral rhodium(I)-binap [2,2′-bis(diphenylphosphino)-1,1′-binaphthyl] catalyst: the enantiocontrolled asymmetric synthesis of (–)-(S)-physoperuvine

Catalytic asymmetrization of meso-3,7-bis-tert-butyldimethylsiloxycycloheptene occurs in the presence of a chiral rhodium(I) binap catalyst to give optically active 4-tert-butyldimethylsiloxycycloheptanone in 70% ee after hydrolytic workup, the (R)-enantiomer of which has been transformed into (-)–(S)-physoperuvine, the major alkaloid of Physalis peruviana.

New hydroformylation rhodium catalysts with dithiolate chiral ligands

Asymmetric hydroformylation of styrene is performed using the bridge dithiolate chiral rhodium complexes [Rh 2(μ-(−)-DIOS)(cod) 2] n n=2 ( 1); and n=1 ( 2); ((−)-DIOS: 2,3- O-isopropylidene-1,4-dithiO- L-threitol and cod: 1,5-cyclooctadiene) as catalyst precursors. The catalytic system 1 provides high conversion in the corresponding aldehydes (100% at 30 bar, 65°C) with a selectivity in 2-phenylpropanal of 64%. Addition of PPh 3 to the catalytic system 1 increases the selectivity in 2-phenylpropanal to 91 % in the same conditions. Although the ee's obtained using 1 were low (3–5%), the addition of a chiral phosphine, (+)-DIOP ((2 S,3 S)-2,3- O-isopropylidene-2,3-dihydroxy-1,4-bis (diphenylphosphino)butane), improves the ee in ( S)-2-phenylpropanal to 17%. However the addition of (−)-DIOP gives a lower ee (3% ( S)). Comparative results were obtained using 2 as catalyst precursor indicating that similar species were formed during catalytic cycle.

Chiral rhodium carboxylates as asymmetric hydrogenation catalysts

The comparative catalytic activities of a few chiral rhodium carboxylato complexes in combination with chiral and achiral phosphines are described. In the hydrogenation of α-acetamidocinnamic acid and its methyl ester, differences are observed in turnover numbers and enantioselectivities. Diastereomeric interactions between chiral carboxylato and chiral phosphine moieties resulting in different rates are clearly seen. Arrhenius plots of (+) and (-) DIOP [DIOP = 2,3 isopropylidene 2,3 dihydroxy-1,4bis (diphenylphosphino) butane] with rhodium (-) mandalato complex give markedly different activation energies.

Asymmetric Catalysis. Asymmetric Catalytic Intramolecular Hydroacylation of 4-Pentenals Using Chiral Rhodium Diphosphine Catalysts

Catalysts of the type [Rh(chiral diphosphine)] + convert 4-substituted 4-pentenals into the corresponding 3-substituted cyclopentanones with generally high turnover numbers and frequencies at 25 o C. The enantioselectivities of various substituted 4-pentenals with two chiral diphosphines have been explored. It was found that with the binap catalyst, almost complete enantioselectivity is observed for 4-pentenal substrates bearing 4-substituted tertiary substituents and for ester groups. Ketonic substituents give very high enantioselectivities

ChemInform Abstract: Highly Diastereoselective, Enantioselective Cyclization of Symmetrical 3,4‐Disubstituted 4‐Pentenal Using Chiral Rhodium(I) Complex.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Chiral Rhodium Complex‐Catalyzed Asymmetric Cyclization and Its Application to the Synthesis of Natural Products

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Discrete Chiral Rhodium Phosphine Complexes as Catalysts for Asymmetric Hydrosilation of Ketones

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Highly diastereoselective, enantioselective cyclization of symmetrical 3,4-disubstituted 4-pentenal using chiral rhodium(I)-complex

Concurrent introduction of two chiral centers at 3,4-positions of cyclopentanone from symmetrical 1 was achieved in diastereoselective and enantioselective fashion by combination of BINAP and cationic Rh(I)(or neutral).

ChemInform Abstract: Enantiocontrol and Regiocontrol in Lactam Syntheses by Intramolecular Carbon‐Hydrogen Insertion Reactions of Diazoacetamides Catalyzed by Chiral Rhodium(II) Carboxamides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Diastereoselective Hydrogenation of Monodehydro Enkephalins Controlled by Chiral Rhodium Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.