Rhodium-Catalyzed Conjugate Addition Research Articles

Cage-Shaped Phosphites Having C3 -Symmetric Chiral Environment: Steric Control of Lewis Basicity and Application as Chiral Ligands in Rhodium-Catalyzed Conjugate Additions.

Designing chiral ligands with an axial symmetry higher than C2 -rotational symmetry is one of the most crucial approaches to improving enantioselectivity in asymmetric synthesis. Herein, C3 -symmetric chiral cage-shaped phosphites are reported. Their Lewis basicity and chiral environment are precisely controlled by the tethered group. The cage-shaped phosphites successfully worked as chiral ligands in Rh-catalyzed asymmetric conjugate additions, realizing acceptable yields with excellent enantioselectivity, and were used to synthesize a pharmacologically important molecule.

Accessing Phase-Transfer Catalysts and a Phosphoramidite Ligand via the Asymmetric Intramolecular Hydroamination Reaction

Within the last few years, our group has developed the intramolecular, asymmetric hydroamination (HA) reaction to a point where essentially enantiopure products can be obtained. The question then arose as to whether we can apply the reaction in useful ways beyond the synthesis of natural/pharmaceutically relevant products. In the present paper, we incorporate a select few HA products for the production of new chiral phase-transfer catalysts. These species are synthesized in one or two synthetic steps from new spirocyclic HA products and are applied in a classical substitution reaction, showing negligible enantioselectivity. In a second application, we introduce a novel phosphoramidite ligand, obtained by combining BINOL (1,1′-bi-2-naphthol) and an optically pure HA product with phosphorous trichloride. The representative ligand shows high enantioselectivity and activity in the rhodium-catalyzed conjugate addition reaction (Hayashi–Miyaura reaction).

Catalytic Enantioselective Synthesis of 1,4-Keto-Alkenylboronate Esters and 1,4-Dicarbonyls.

A catalytic enantioselective method for the synthesis of 1,4-keto-alkenylboronate esters by a rhodium-catalyzed conjugate addition pathway is disclosed. A variety of novel, bench-stable alkenyl gem-diboronate esters are synthesized. These easily accessible reagents react smoothly with a collection of cyclic α,β-unsaturated ketones, generating a new C-C bond and stereocenter. Products are isolated in up to 99 % yield with greater than 20:1 E/Z and greater than 99:1 e.r. Mechanistic studies show the site-selectivity of transmetalation and reactivity is ligand dependent. The utility of the approach is highlighted by gram-scale synthesis of enantioenriched cyclic 1,4-diketones, and stereoselective transformations of the products by hydrogenation, allylation, and isomerization.

Rhodium-Catalyzed Conjugate Addition Towards Chiral Thioflavanones

Rhodium-Catalyzed Conjugate Addition Towards Chiral Thioflavanones

Trans-selective rhodium catalysed conjugate addition of organoboron reagents to dihydropyranones.

The selective synthesis of 2,6-trans-tetrahydropyran derivatives employing the rhodium catalysed addition of organoboron reagents to dihydropyranone templates, derived from a zinc-catalysed hetero-Diels-Alder reaction, is reported. The addition of both arylboronic acids and potassium alkenyltrifluoroborates have been accomplished in high yields using commercially-available [Rh(cod)(OH)]2 catalyst. The selective formation of the 2,6-trans-tetrahydropyran stereoisomer is consistent with a mechanism involving alkene association and carbometalation on the less hindered face of the dihydropyranone.

Bicyclic Bridgehead Phosphoramidite (Briphos) Ligands with Tunable π-Acceptor Ability and Catalytic Activity in the Rhodium-Catalyzed Conjugate Additions

A new type of bicyclic bridgehead phosphoramidites (briphos) is reported, where the geometrical constraints significantly enhance the π-acceptor ability compared with its monocyclic analogs. The briphos is shown to be highly efficient and tunable for Rh(I)-catalyzed conjugate additions of aryl boronic acids to α,β-unsaturated ketones and N-tosyl ketimines.

Total Synthesis of (R)-Sarkomycin via Asymmetric Rhodium-Catalyzed Conjugate Addition

(R)-Sarkomycin was prepared using a five-step total synthesis. Key steps in the enantioselective construction of the targeted scaffold were a rhodium-catalyzed asymmetric conjugate alkenyl addition with subsequent silyl trapping and a Mukaiyama aldol reaction with aqueous formaldehyde. Protection of the hydroxy group as a THP acetal and oxidative cleavage of the C,C-double bond provided a stable direct precursor to the natural product. The final liberation was carried out under slightly acidic conditions in a microwave-assisted reaction, resulting in a high yield of the "deceptive" sarkomycin. This represents the shortest enantioselective synthesis of this rather unstable compound to date and the first to employ asymmetric catalysis to introduce the stereogenic center.

Rhodium(i)-catalyzed 1,4-conjugate arylation toward β-fluoroalkylated electron-deficient alkenes: a new entry to a construction of a tertiary carbon center possessing a fluoroalkyl group

Treatment of β-fluoroalkylated-α,β-unsaturated ketones with 1.2 equiv. of various arylboronic acids in the presence of 5 mol% of [Rh(COD)(2)]BF(4) and 6 mol% of (S)-BINAP in toluene/H(2)O (v/v = 4/1) at the reflux temperature for 3 h gave the corresponding Michael adducts in high yields with over 90% enantioselectivity. Though other electron-deficient alkenes, such as vinylsulfone and vinylphosphonate, were found to be much less reactive in the rhodium-catalyzed conjugate addition with arylboronic acids, the reaction of various arylstannanes toward such electron-deficient alkenes took place very smoothly to afford the corresponding adducts in high yields.

Rhodium-catalyzed conjugate addition of arylindium reagents to α,β-unsaturated carbonyl compounds

A novel rhodium-catalyzed conjugate addition of indium reagents to electron deficient olefins is reported. The reaction takes place in THF/MeOH at 110 °C using arylindium dichlorides, a rhodium(I)-binap complex as catalyst, and α,β-unsaturated ketones and lactones in good yields (45–94%). The addition of MeOH is crucial for an efficient transformation and NMR studies seem to indicate that promotes the catalytic cycle leaving the indium organometallic unaltered. The use of chiral non-racemic ligands allows performing the reaction with moderate enantioselectivities.

Enantioselective Rhodium-Catalyzed Conjugate Addition

In this report, the authors describe their use of chiral olefin-sulfinimide ligands in the conjugate addition to enones. The synthesis of these ligands is relatively easy and allows for diverse structures, rendering them attractive ligands for asymmetric synthesis.

Novel Ligand for Rh-Catalyzed Asymmetric Conjugate Addition

This paper describes the development of a new class of chiral olefin-sulfur ligands for enantioselective rhodium-catalyzed conjugate addition of boronic acids to various enones. The corresponding products can be obtained in good to excellent yield and enantioselectivity.

Rhodium-Catalyzed Asymmetric Conjugate Addition withN-Sulfinyl Ligands

Rhodium-Catalyzed Asymmetric Conjugate Addition with<i>N</i>-Sulfinyl Ligands

Acyclic Chiral Diene Ligands for Rhodium(I)-Catalyzed Conjugated Additions

In recent years, chiral dienes have attracted considerable attention as ligands for transition-metal-catalyzed enantioselective reactions. However, the developed catalysts are predominantly based on bicyclic systems, which sometimes cannot be obtained easily; in this context, acyclic ligands are of great importance. In this paper, straightforward syntheses of novel acyclic diene ligands are described. The use of ligand 1 allowed the rhodium-catalyzed conjugate addition of boronic acids to α,β-unsaturated compounds with 54-99% yields and 76-95% ee.

Exploring Rhodium-Catalysed Conjugate Addition of Chiral Alkenylboronates Using Chiral Olefin Ligands

The rhodium-catalysed addition of chiral alkenylboron reagents to prochiral α,β-unsaturated carbonyl acceptors are demonstrated to proceed under ligand control. The highest activities were obtained with chiral olefin ligands and the configuration of the new stereocentre can be predicted by using established models.

Electronically Tunable Chiral Ligands for Rhodium-Catalyzed Conjugate Addition

Electronically Tunable Chiral Ligands for Rhodium-Catalyzed Conjugate Addition

Alternatives to Organoboron Reagents in Rhodium‐Catalyzed Conjugate Additions

The rhodium-catalyzed conjugate addition of organoboron reagents to alkene acceptors has emerged as an important methodology in organic synthesis. The process results in the formation of new carbon-carbon bonds, and in principle, can create new stereocenters at both the alpha and beta carbon atoms of the acceptor. Other organometallics are known to participate in the key transmetalation to rhodium and are becoming more established in stereoselective synthesis (notably arylzinc reagents). This Focus Review will describe recent developments in the use of alternative organometallic donors to organoboron reagents in rhodium-catalyzed conjugate addition reactions and their growing applications in synthesis.

Synthetic applications of rhodium catalysed conjugate addition

The rhodium catalysed conjugate addition of organometallics to activated alkenes is a powerful synthetic tool for establishing new carbon-carbon bonds often with high stereoselectivity. The introduction of a practical, efficient method for introducing functionalised aryl and alkenyl fragments with predictable stereocontrol has caught the attention of synthetic chemists and emerging examples are growing in number and complexity. In this tutorial review, we document notable advances in the application of rhodium catalysed conjugate addition processes within the context of synthesis of complex molecules and intermediates in drug discovery. The chosen examples illustrate important issues regarding scope, selectivity and reactivity that will help guide the selection of appropriate donor and acceptor to achieve the desired carbon-carbon bond construction when planning new synthetic routes.

Rhodium-catalysed conjugate addition of arylboronic acids to enantiopure dehydroamino acid derivatives

The rhodium-catalysed conjugate addition of arylboronic acids to an enantiopure acceptor derived from (R)-S-methylcysteine proceeds under substrate control to provide a range of functionalised phenylalanine derivatives with excellent stereocontrol via a highly diastereoselective protonation.

Novel, Efficient Alkene-Phosphinite Hybrid Ligand Based on d-Glucose

A commercially available 2,3-unsaturated pyranoside, derived from d-glucose, was converted into a new type of olefin phosphorus chelate ligand in only three steps. Application in rhodium catalyzed conjugate additions of phenylboronic acid to enones led to excellent levels of stereoinduction for several cyclic substrates. The easy preparation and the high efficiency of this ligand make it an interesting and promising alternative to established systems.

Rhodium-Catalyzed Conjugate Addition of Sb-Aryl-1,5-azastibocines to α,β-Unsaturated Carbonyl Compounds

Rhodium-catalyzed conjugate addition of Sb-aryl-1,5-azastibocines to α,β-unsaturated carbonyl compounds is described. The rhodium-catalyzed reaction was carried out in aqueous N-methy-2-pyrrolidinone (NMP) to give 1,4-conjugate adduct exclusively, while the palladium catalyzed reaction gave only Heck-type adduct. The 1,4-addition of various aryl groups such as substituted benzenes and thiophenes was achieved with various enones and enoates.