Chiral Rhodium Research Articles

Catalytic enantioselective tandem carbonyl ylide formation—intramolecular cycloaddition with unsaturated α-diazo-β,ε-diketo sulfones

The synthesis and 1,3-dipolar cycloaddition reactions of unsaturated α-diazo-β,ε-diketo sulfones 7 using chiral rhodium catalysts (up to 71.5:28.5 er) are described.

Transition‐Metal‐Catalyzed Enantioselective [2+2+2] Cycloadditions for the Synthesis of Axially Chiral Biaryls

Recent advances towards a development of novel transition-metal-catalyzed enantioselective [2+2+2] cycloadditions for the synthesis of axially chiral biaryls are reviewed. A number of efficient enantioselective biaryl syntheses were accomplished by chiral cobalt(I), iridium(I), and rhodium(I) complex catalyzed [2+2+2] cycloadditions. Furthermore, the enantioselective synthesis of axially chiral biaryls possessing non-biaryl axial chirality was also developed by using chiral rhodium(I) complexes as catalysts.

Regiodivergent Resolution of Unsymmetrical Oxabicyclic Alkenes

The Lautens group reports a rare example of a regiodivergent resolution of bridgehead-substituted oxabenzonorbornene derivatives under rhodium catalysis. From earlier work, these oxabicycles were shown to undergo [Rh(CO)2Cl]2-catalyzed addition of methanol to provide product type A based on complete substrate control. However, when these substrates were treated with a chiral rhodium complex, two regioisomers (type A and B) resulting from Rh insertion into either C-O bond were obtained each in excellent enantioselectivity. Subsequently, various oxabi­cycles and alcohol- and amine-based nucleophiles could be used under these reaction conditions.

Intermolecular Antiselective and Enantioselective Reductive Coupling of Enones and Aromatic Aldehydes with Chiral Rh(Phebox) Catalysts

The intermolecular reductive coupling reaction of cyclopent-2-enone and aromatic aldehydes was realized by chiral rhodium-(bisoxazolinyl)phenyl catalysts, Rh(Phebox-Ph)(OAc)(2)(H(2)O), with diphenymethylsilane as a hydride donor to give the corresponding beta-hydroxyketones in high anti-selectivity (up to 96%) with high enantioselectivity (up to 93%).

Synthesis of Chiral C2-symmetric Palladium and Rhodium SCS Pincers

Synthesis of Chiral C₂-symmetric Palladium and Rhodium SCS Pincers

Asymmetric β-boration of α,β-unsaturated carbonyl compounds promoted by chiral rhodium–bisoxazolinylphenyl catalysts

Chiral rhodium-bisoxazolinylphenyl acetate complexes exhibited high catalytic activity for the beta-boration of alpha,beta-unsaturated carbonyl compounds with bis(pinacolato)diboron in the presence of sodium t-butoxide with enantioselectivity up to 97%.

Enantioselective CC Bond Activation of Allenyl Cyclobutanes: Access to Cyclohexenones with Quaternary Stereogenic Centers

Chiral rhodium(I) complexes activate allenyl tert-cyclobutanols efficiently through enantioselective insertion into a CC σ bond of the cyclobutane (see scheme; cod=1,5-cyclooctadiene, DTBM=3,5-di-tert-butyl-4-methoxyphenyl). Ring expansion by this method produced cyclohexenones with quaternary stereogenic centers with excellent enantioselectivity. The catalyst loading can be decreased to just 0.1 mol % in rhodium. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: A Chiral Rhodium Carboxamidate Catalyst for Enantioselective C—H Amination.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

Enantioselective synthesis of 1-arylethanediols by rhodium-catalyzed transfer hydrogenation of α-tosyloxyarylketones

AbstractCatalytic transfer hydrogenation of α-tosyloxyarylketones mediated by a chiral rhodium complex using an azeotropic mixture of formic acid/triethylamine afforded the corresponding 1-arylethanediol monotosylates in excellent yield with high enantioselectivity.Graphical abstract[IMAGE]

A chiral rhodium carboxamidate catalyst for enantioselective C-H amination.

Rh2(S-nap)4, a chiral dirhodium tetracarboxamidate complex, has been developed and shown to be an effective catalyst for the asymmetric, intramolecular C-H amination of sulfamate esters. Enantiomeric excesses range from 60-99% for a collection of disparately substituted 3-arylpropylsulfamates. In addition, Rh2(S-nap)4 is found to promote chemoselective allylic C-H oxidation of unsaturated sulfamates, a property not observed with other dirhodium complexes tested to date.

Access to Enantioenriched α-Amino Esters via Rhodium-Catalyzed 1,4-Addition/Enantioselective Protonation

Conjugate addition of potassium trifluoro(organo)borates 2 to dehydroalanine derivatives 1, mediated by a chiral rhodium catalyst and in situ enantioselective protonation, afforded straightforward access to a variety of protected alpha-amino esters 3 with high yields and enantiomeric excesses up to 95%. Among the tested chiral ligands and proton sources, Binap, in combination with guaiacol (2-methoxyphenol), an inexpensive and nontoxic phenol, afforded the highest asymmetric inductions. Organostannanes have also shown to participate in this reaction. By a fine-tuning of the ester moiety, and using Difluorophos as chiral ligand, increased levels of enantioselectivity, generally close to 95%, were achieved. Deuterium labeling experiments revealed, and DFT calculation supported, an unusual mechanism involving a hydride transfer from the amido substituent to the alpha carbon explaining the high levels of enantioselectivity attained in controlling this alpha chiral center.

Stereochemical Nonrigidity of a Chiral Rhodium Boryl Hydride Complex: A σ-Borane Complex as Transition State for Isomerization

Experimental and computational studies are reported on half-sandwich rhodium complexes that undergo B-H bond activation with pinacolborane (HBpin = HB(OCMe2CMe2O)). The photochemical reaction of [Rh(eta5-C5H5)(R,R-phospholane)(C2H4)] 3 (phospholane = PhP(CHMeCH2CH2CHMe)) with HBpin generates the boryl hydride in two distinguishable isomers [(SRh)-Rh(eta5-C5H5)(Bpin)(H)(R,R-phospholane)] 5a and [(RRh)-Rh(eta5-C5H5)(Bpin)(H)(R,R-phospholane)] 5b that undergo intramolecular exchange. The presence of a chiral phosphine allowed the determination of the interconversion rates (epimerization) by 1D 1H EXSY spectroscopy in C6D6 solution yielding DeltaH = 83.4 +/- 1.8 kJ mol-1 for conversion of 5a to 5b and 79.1 +/- 1.4 kJ mol-1 for 5b to 5a. Computational analysis yielded gas-phase energy barriers of 96.4 kJ mol-1 determined at the density functional theory (DFT, B3PW91) level for a model with PMe3 and B(OCH2CH2O) ligands; higher level calculations (MPW2PLYP) on an optimized QM/MM(ONIOM) geometry for the full system place the transition state 76.8 kJ mol-1 above the average energy of the two isomers. The calculations indicate that the exchange proceeds via a transition state with a sigma-B-H-bonded borane. The B-H bond lies in a mirror plane containing rhodium and phosphorus. No intermediate with an eta2-B-H ligand is detected either by experiment or calculation. Complex 3 has also been converted to the [Rh(eta5-C5H5)Br2(R,R-phospholane)] (characterized crystallographically) and [Rh(eta5-C5H5)(H)2(R,R-phospholane)]. The latter exhibits two inequivalent hydride resonances that undergo exchange with DeltaH = 101 +/- 2 kJ mol-1. DFT calculations indicate that the boryl hydride complex has a lower exchange barrier than the dihydride complex because of steric hindrance between the phospholane and Bpin ligands in the boryl hydride.

Enantioselective Syntheses of Various Chiral Multicyclic Compounds with Quaternary Carbon Stereocenters by Catalytic Intramolecular Cycloaddition

The intramolecular cycloaddition of 1,n-diene-ynes (n = 4-6), where alkyne and alkene moieties are connected by a 1,1-disubstituted alkene, was examined using a chiral rhodium catalyst, and various types of cycloadducts with quaternary carbon stereocenter(s) were obtained in high to excellent enantiomeric excess. In the case of 1,4-diene-ynes, tricyclic, bicyclic, and spirocyclic compounds were obtained depending upon the substituents at the 2-position of the 1,4-diene moiety and those at their alkyne termini. On the other hand, 1,5- and 1,6-diene-ynes gave tricyclic and bicyclic compounds, which included medium-sized ring systems. The mechanistic considerations for different reaction pathways and the synthetic transformation of tricyclic products into functionalized spirocyclic compounds are also described. The reaction of enediynes, where two alkyne moieties are connected by a 1,1-disubstituted alkene, was also examined, and sterically strained tricyclic compounds with two carbon stereocenters were obtained.

ChemInform Abstract: Fluorinated Alcohols as Solvents for Enantioselective Hydrogenation with Chiral Self‐Assembling Rhodium Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

Recent advances in enantioselective [2 + 2 + 2] cycloaddition

Enantioselective cycloaddition using chiral transition metal catalysts is an atom-economical and efficient synthetic tool for the construction of chiral carbo- and heterocyclic skeletons. This short account discloses our recent results of inter- and intramolecular enantioselective [2 + 2 + 2] cycloadditions of alkyne and/or alkene moiety(ies). Chiral iridium complexes catalyzed the alkyne trimerization for the generation of axial chirality(ies), and chiral rhodium ones catalyzed alkyne-alkyne-alkene cyclization for the generation of a quaternary carbon including spirocyclic system.

Asymmetric Hydrogenation of Unsaturated Ureas with the BIPI Ligands

Asymmetric hydrogenation of unsaturated urea esters with the BIPI Ligands has been examined. Optimization of the P-N ligand structure has led to the development of chiral rhodium catalysts capable of producing the targets with >99% ee. The critical phosphine borane SNAr reaction needed for ligand synthesis has been optimized to give the adducts in high yield at ambient temperature with no racemization. An extremely concise, economical, and scalable sequence to these important new ligands for catalysis of asymmetric hydrogenation has been developed.

Synthesis and characterization of asymmetric NHC complexes

New chiral and non-chiral rhodium(I)–NHC complexes were synthesized. The first attempt by deprotonation of an imidazolinium salt with KO tBu and reaction with [Rh(COD)Cl] 2 leads to the corresponding rhodium(I) complex. Due to the basic conditions during the reaction a loss of chirality occurs. An alternative transmetallation reaction with a silver(I)–NHC complex yields the desired rhodium(I)–NHC complex under retention of chirality. Both Rh complexes were fully characterized by analytical methods.

Rhodium-catalyzed enantioselective [2+2+2] cycloaddition of diynes with unfunctionalized alkenes

A chiral rhodium complex catalyzed an enantioselective [2+2+2] cycloaddition of unsymmetrical diynes with norbornene, and tetracyclic products were obtained in good to excellent ee. The cycloaddition of a symmetrical diyne with styrene derivatives as coupling partners gave bicyclic products in good ee.

De novo Synthesis of Troc‐Protected Amines: Intermolecular Rhodium‐Catalyzed C—H Amination with N‐Tosyloxycarbamates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Crystallization of zeolite beta in the presence of chiral amine or rhodium complex

Crystallization methods of zeolite beta in an acidic medium at low temperature (pH 4, 373 K) were developed. Zeolite beta was crystallized in the presence of chiral amine or rhodium complex as secondary structure directing agents (SDAs) in the acidic condition whose advantage was high solubility of the chiral amines. The secondary SDAs with C 2 symmetry induced the crystallization of zeolite beta which contained a somewhat large fraction of polymorph A.