Rhodium-Catalyzed Conjugate Addition Research Articles

New Chiral Diene Ligands for Rhodium-Catalyzed Conjugate Additions

Recently, Hayashi and others have introduced a new class of chiral bicyclic dienes which have been shown to be superior to bisphosphines as ligands in various transition-metal- ­catalyzed reactions. Unfortunately, the synthesis of many of these ligands is not trivial, limiting their broad applicability. In the present report, ­Okamoto, Hayashi and Rawal disclose a direct, two-step route to chiral diene L1 from commercially available (R)-(-)-α-phellandrene. Remarkably, in rhodium-catalyzed conjugate addition reactions L1 displayed higher levels of selectivity than several other well-known chiral dienes.

Stereoselective Rhodium-Catalyzed Conjugate Addition of Boronic Acids to Unprotected δ-Hydroxy-γ-butenolides. Synthesis of (−)-7-Oxamuricatacin and β-Substituted Derivatives

The chiral delta-hydroxy-gamma-butanolide moiety is widely found among biologically active natural products. We report herein the stereoselective synthesis of beta-substituted analogues of these compounds by the Rh(I)-catalyzed conjugate addition of boronic acids to chiral delta-hydroxy-gamma-butenolides, easily prepared from the chiral pool. The reaction takes place with high trans diastereoselectivity without protection of the hydroxyl group. The three-step syntheses of (-)-7-oxamuricatacin (R1 = H, R2 = CH2-O-(n)C10H21) and of new beta-substituted 7-oxamuricatacin analogues (R1 = aryl, vinyl) is reported.

Rhodium-Catalyzed Conjugate Addition of Sterically Bulky Silylacetylene to Enones

Rhodium-Catalyzed Conjugate Addition of Sterically Bulky Silylacetylene to Enones

Rhodium-Catalyzed Conjugate Addition of Boronic Acids to Vinyl 2-Pyridyl Sulfones

Rhodium-Catalyzed Conjugate Addition of Boronic Acids to Vinyl 2-Pyridyl Sulfones

Sequential Rh(I)/Pd-Catalyzed 1,4-Addition/Intramolecular Allylation: Stereocontrolled Construction of γ-Butyrolactones and Cyclopropanes

The rhodium-catalyzed conjugate addition of functionalized vinyltin reagents to alkylidene Meldrum's acids, followed by Pd-catalyzed intramolecular allylation, is a direct entry into vinyl-substituted gamma-lactones via O-alkylation and vinylcyclopropanes via C-alkylation.

Rhodium catalysed conjugate addition of a chiral alkenyltrifluoroborate salt: the enantioselective synthesis of hermitamides A and B

The concise enantioselective synthesis of hermitamides A and B is presented utilising a rhodium catalysed conjugate addition reaction to introduce the side chain and chiral information in a single step via an alkenyltrifluoroborate salt.

Highly Selective Rhodium-Catalyzed Conjugate Addition Reactions of 4-Oxobutenamides

A variety of 4-oxobutenamides 1 were subjected to rhodium-catalyzed conjugate addition with arylboronic acids providing high regio- and enantioselectivity (97:3 to >99:1, >96% ee) and moderate to excellent yields (54-99%). The key to high selectivity is the use of sterically demanding P-chiral diphosphines, such as Tangphos or Duanphos. The product oxobutanamides 2 may be converted to alternate targets by selective derivatization of either the amide or ketone functional group. A stereochemical model predicting the absolute sense of induction was developed based on single-crystal X-ray structures of product and precatalyst.

Rhodium-Catalyzed Conjugate Addition−Enantioselective Protonation: The Synthesis of α,α‘-Dibenzyl Esters

Alpha-benzyl acrylates, which are conveniently prepared from the corresponding aldehydes, can be employed as substrates in a tandem rhodium-catalyzed conjugate addition-enantioselective protonation protocol to afford enantiomerically enriched alpha,alpha'-dibenzyl esters. The synergistic effect of enantiopure ligand and proton source was rapidly optimized with use of a microwave reactor.

Rhodium-Catalyzed Conjugate Additions of Boronic Acids to Enones

This paper presents a new chiral bisphosphine ligand that was shown to be effective for rhodium-catalyzed conjugate addition of boronic acids. A four-step procedure starting from racemic 2,5-norbornadione (involving resolution with (R,R)-2,3-diphenylaminocarbonyl tartaric acid provides a new chiral bisphosphine architecture. The conjugate addition reaction has a wide substrate scope of various aryl boronic acids and ­acceptors ranging from 5-7-membered enones that all gave high yields and high enantioselectivities.

Catalytic Asymmetric Synthesis with Rh—Diene Complexes: 1,4‐Addition of Arylboronic Acids to Unsaturated Esters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric Synthesis of 3,3‐Diarylpropanals with Chiral Diene—Rhodium Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enantioselective Rhodium Enolate Protonations. A New Methodology for the Synthesis of β2‐Amino Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly enantioselective rhodium-catalyzed conjugate addition of arylboronic acids to enones at room temperature

The rhodium–phosphoramidite-catalyzed asymmetric conjugate addition of arylboronic acids to enones proceeds at room temperature using [Rh(OH)(cod)] 2 or [RhCl(cod)] 2/KOH as stable and readily available catalyst precursors.

Catalytic Asymmetric Synthesis with Rh−Diene Complexes: 1,4-Addition of Arylboronic Acids to Unsaturated Esters

A general route to enantioenriched tert-butyl 3,3-diarylpropanoates is presented. These useful building blocks are prepared via an asymmetric rhodium-catalyzed conjugate addition of arylboronic acids to unsaturated tert-butyl esters in the presence of chiral dienes as ligands. The addition of both electron-poor and electron-rich boronic acids proceeds smoothly with various enoates in 63-90% yield with high enantioselectivites (89-94% ee). [reaction: see text]

Asymmetric Synthesis of 3,3-Diarylpropanals with Chiral Diene−Rhodium Catalysts

A general route to enantioenriched 3,3-diarylpropanals is presented. These useful building blocks are prepared via an asymmetric rhodium-catalyzed conjugate addition of arylboronic acids to cinnamaldehyde derivatives in the presence of chiral dienes. The addition of both electron-poor as well as electron-rich boronic acids proceeds smoothly with various enals in 63-90% yield with high enantioselectivities (89-93% ee).

Enantioselective Rhodium Enolate Protonations. A New Methodology for the Synthesis of β2-Amino Acids

[reaction: see text] Rhodium-catalyzed conjugate addition of an aryl boronic acid to alpha-methylamino acrylates followed by enantioselective protonation of the oxa-pi-allylrhodium intermediate provides access to aryl-substituted beta(2)-amino acids. The impact of the different variables of the reaction on the levels of enantioselectivity has been assessed.

Enantioselective conjugate addition of phenylboronic acid to enones catalysed by a chiral tropos/atropos rhodium complex at the coalescence temperature

A highly enantioselective rhodium-catalysed conjugate addition of phenylboronic acid to cyclic enones has been achieved using a dynamic library of chiral phosphorus ligands; the tropos/atropos nature of the ligands in the rhodium complex has been characterised via 31P-NMR.

Desymmetrization of enone-diones via rhodium-catalyzed diastereo- and enantioselective tandem conjugate addition-aldol cyclization

Catalytic tandem conjugate addition-enolate trapping represents an effective strategy for the design of catalytic transformations that enable formation of multiple C-C bonds. Recently, using enantioselective rhodium-catalyzed conjugate addition methodology, we developed a catalytic tandem conjugate addition-aldol cyclization of keto-enones. Here, we report related desymmetrizations and parallel kinetic resolutions involving the use of diones as terminal electrophiles. The Rh-enolate generated on enone carbometallation effectively discriminates among four diastereotopic pi-faces of the appendant dione, ultimately providing products that embody four contiguous stereocenters, including two adjacent quaternary centers, with quantitative diastereoselection and high levels of enantiomeric excess. This methodology allows concise entry to optically enriched seco-B ring steroids possessing a 14-hydroxy cis-fused C-D ring junction, as found in naturally occurring cardiotonic steroids derived from digitalis.

First Examples of Improved Catalytic Asymmetric C—C Bond Formation Using the Monodentate Ligand Combination Approach.

AbstractFor Abstract see ChemInform Abstract in Full Text.

First examples of improved catalytic asymmetric C-C bond formation using the monodentate ligand combination approach.

[reaction: see text] Using a combination of chiral monodentate phosphoramidite ligands in the rhodium-catalyzed conjugate addition of boronic acids to three different substrates, we have shown for the first time that the ligand combination approach is applicable for C-C bond formation. Chiral catalysts based on hetero-combinations of ligands are found to be more effective than the homo-combinations. (31)P NMR experiments show that the hetero-combinations are formed in excess over the homo-combinations.