Enantioselective Copper-Catalyzed Conjugate Addition of Trimethylaluminium to β,γ-Unsaturated α-Ketoesters

Enantioselective Mukaiyama-Michael Reaction of β,γ-Unsaturated α-Keto Esters with Silyl Ketene Acetals Catalyzed by a Chiral Magnesium Phosphate

We would like to describe an efficient and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with β,γ-unsaturated α-keto esters catalyzed by a chiral magnesium BINOL-derived phosphate. The resulting functionalized 1,5-dicarbonyl adducts are obtained in high yields (up to 96%) and with excellent enantioselectivities (up to 98%) under mild conditions. Two plausible mechanistic pathways were proposed, including a 1,4-addition and a hetero Diels-Alder [4 + 2] cycloaddition.

Base-promoted [4 + 2] annulation of pyrrole-2-carbaldehyde derivatives with β,γ-unsaturated α-ketoesters: syntheses of 5,6-dihydroindolizines

A base-promoted [4 + 2] annulation of pyrrole-2-carbaldehyde derivatives with β,γ-unsaturated α-ketoesters for the syntheses of multisubstituted 5,6-dihydroindolizines was developed.

Organocatalyzed Enantioselective Conjugate Addition of Boronic Acids to β,γ-Unsaturated α-Ketoesters

We report herein the (R)-3,3'-Br₂-BINOL-catalyzed enantioselective conjugate addition of organic boronic acids to β,γ-unsaturated α-ketoesters to generate the corresponding Michael addition products in moderate to high yields and with moderate to excellent enantioselectivities (up to 99% ee). This catalytic system features characteristics of mild reaction conditions, high efficiency, and tolerance to alkenylboronic acids and heteroarylboronic acids.

Bi(OAc)3/Chiral Phosphoric Acid-Catalyzed Enantioselective 1,2- and Formal 1,4-Allylation Reaction of β,γ-Unsaturated α-Ketoesters

A highly efficient asymmetric 1,2-allylation reaction of β,γ-unsaturated α-ketoesters was realized by using a Bi(OAc)₃/chiral phosphoric acid catalyst system under mild conditions. Meanwhile, using this combined strategy of enantioselective 1,2-allylation and subsequent anionic oxy-Cope rearrangement, the asymmetric formal 1,4-allylation reaction was achieved by a one-pot process. These reactions offer rapid access to an array of homoallylic tertiary alcohols and γ-allyl-α-ketoesters with good yields and excellent enantioselectivities. Density functional theory calculations were conducted to interpret the high enantioselectivity.

Palladium-Catalyzed Synthesis of 1,2-Diketones from Aryl Halides and Organoaluminum Reagents Using tert-Butyl Isocyanide as the CO Source

In this work, an interesting and practical procedure for the synthesis of 1,2-diketones from aryl halides and organoaluminum reagents has been developed. Employing tert-butyl isocyanide as the CO source and palladium as the catalyst, the desired 1,2-diketones were isolated in good to excellent yields with good functional group tolerance. Concerning the reaction partners, besides aryl halides, both alkyl- and arylaluminum reagents were all suitable substrates here.

Photoinduced Multicomponent Synthesis of α-Silyloxy Acrylamides, an Unexplored Class of Silyl Enol Ethers

The photoinduced, multicomponent reaction of α-diazoketones, silanols, and isocyanides affords α-silyloxy acrylamides, formally derived from α-keto amides. The presence of a secondary amido group makes classic preparative methods for silyl enol ethers unfeasible in this case, while the mild conditions required by this photochemical approach allow their synthesis in good yields; moreover, the general structure can be easily modified by varying each component of the multicomponent reaction. Fine-tuning of the reaction conditions (i.e., solvents, radiation, additives) can be exploited to obtain complete Z selectivity. The reactivity of this overlooked class of silyl enol ethers has been investigated, and features that could pave the way to new applications have been found.

Synthesis of 1,2-Dicarbonyl-3-enes by Hydroacylation of 1-Alkynes with Glyoxal Derivatives Using Metal-Organic Framework Cu/MOF-74 as Heterogeneous Catalyst

A crystalline copper-based metal-organic framework Cu/MOF-74 was synthesized, and used as an efficient heterogeneous catalyst for the synthesis of 1,2-dicarbonyl-3-enes by means of the hydroacylation of 1-alkynes with glyoxal derivatives in the presence of a base. Cu/MOF-74 was found to be more catalytically active for the synthesis of 1,2-dicarbonyl-3-enes than other MOFs including Cu₂ (BDC)₂ (DABCO), Cu₃ (BTC)₂ , Cu(BDC), Cu₂ (NDC)₂ (DABCO), Cu₄ I₄ (DABCO)₂ , Ni-MOF-74, Zn-MOF-74, Fe₃ O(BDC)₃ , In(OH)(BDC), and Zr₆ O₄ (OH)₄ (BDC)₆ . Cu/MOF-74 also exhibited better performance than other homogeneous copper catalysts, including Cu(OAc)₂ , Cu(NO₃ )₂ , CuI, CuBr, CuCl, CuCl₂ , and CuBr₂ . The Cu/MOF catalyst was able to be recovered and reused several times without a significant degradation in catalytic activity. To the best of our knowledge, the formation of 1,2-dicarbonyl-3-enes has not previously been carried out under heterogeneous catalysis conditions.

A concise asymmetric total synthesis for structure elucidation of 5,6-secoiridoid from Incarvillea argute

A phytochemical investigation of the roots of Incarvillea arguta led to the isolation of secoarguterin (1), which is the first example of 5,6-secoiridoid.

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

The copper-catalyzed asymmetric conjugate addition (ACA) of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as it enables in a straightforward manner the sequential generation of two or more stereogenic centers. In the last decade, various chiral copper-based catalysts were evaluated in combination with different nucleophiles and Michael acceptors, and have unambiguously demonstrated their usefulness in the control of the regio- and enantioselectivity of the addition. The aim of this review is to report recent breakthroughs achieved in this challenging field.

A New Strategy for Enantioselective Construction of Multisubstituted Five-Membered Oxygen Heterocycles via a Domino Michael/Hemiketalization Reaction

A new highly enantioselective domino Michael/hemiketalization reaction of α-hydroxyacetophenone with β,γ-unsaturated α-keto esters for the synthesis of 2,2,4,5-tetrasubstituted chiral tetrahydrofurans is reported. With 2 mol % intramolecular dinuclear zinc-AzePhenol complex prepared in situ from the reaction of multidentate semi-azacrown ether ligand with ZnEt2 , the corresponding anti-multisubstituted tetrahydrofuran products were obtained in up to 90 % yields, and 98 % enantiomeric excess (ee) at 0 °C for 45 min. Moreover, the products were easily converted to 2,3,5-trisubstituted 2,3-dihydrofurans without any loss in optical activity.

Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,β-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,β-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.

Stereo-controlled synthesis of polyheterocycles via the diene-transmissive hetero-Diels–Alder reaction of β,γ-unsaturated α-keto esters

Stereocontrolled synthesis of polyheterocycles via the diene-transmissive hetero Diels–Alder reaction of β,χ-unsaturated α-keto esters is described.

Enantioselective phospha-Michael addition of diarylphosphines to β,γ-unsaturated α-ketoesters and amides

An enantioselective hydrophosphination of β,γ-unsaturated α-ketoesters and amides has been developed using a chiral palladacycle catalyst. Adducts can be obtained in excellent yields and enantioselectivities, providing direct access to chiral tertiary phosphines which are synthetically useful intermediates in the preparation of bidentate ligands.

Highly chemo-, enantio-, and regioselective synthesis of α,α-disubstituted furanones by Cu-catalyzed conjugate addition

A highly chemo-, enantio-, and regioselective synthesis of furanones bearing an α,α-disubstituted quaternary stereogenic center is reported. The Cu-catalyzed enantioselective conjugate addition of organoaluminum reagents to unsaturated ketoesters at room temperature and subsequent lactonization took place. Synthetic transformations of furanones represent facile approaches to various cyclic or acyclic compounds bearing a quaternary stereogenic center.

CuBr-promoted formal hydroacylation of 1-alkynes with glyoxal derivatives: an unexpected synthesis of 1,2-dicarbonyl-3-enes

An efficient and concise protocol has been developed for the highly regio- and stereoselective synthesis of E-1,2-dicarbonyl-3-ene derivatives by a copper-promoted reaction of 1-alkynes with α-carbonyl aldehydes in the presence of morpholine. The products obtained are believed as the formal hydroacylation of the triple bond.

Asymmetric decarboxylative 1,4-addition of malonic acid half thioesters to vinyl sulfones: highly enantioselective synthesis of 3-monofluoromethyl-3-arylpropanoic esters

An asymmetric decarboxylative 1,4-addition of malonic acid half thioesters (MAHTs) to 2-aryl-substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97 % ee). In view of tuning pKa values, a quinine-based benzyl-substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3-monofluorinated analogues of 3-methyl indanone and (+)-turmerone has been accomplished from decarboxylative 1,4-addition adducts with satisfactory results.

Reactions of pyruvates: organocatalytic synthesis of functionalized dihydropyrans in one pot and further transformations to functionalized carbocycles and heterocycles

Concise cascade reactions of pyruvates with aldehydes that generate functionalized dihydropyran derivatives in one pot have been developed. The products, dihydropyrans, were further concisely transformed to various functionalized molecules.

A convenient alumination of functionalized aromatics by using the frustrated Lewis pair Et3 Al and TMPMgCl⋅LiCl

A straightforward and efficient alumination of functionalized arenes by using the frustrated Lewis pair Et3 Al and TMPMgCl⋅LiCl (TMP=2,2,6,6-tetramethylpiperidyl) has been developed. In particular, halogenated electron-rich aromatics can be smoothly functionalized by using the frustrated Lewis pair Et3 Al and TMPMgCl⋅LiCl. Compared with previously described alumination methods, this procedure avoids extensive cooling and the need for an excess of base. This in situ procedure has proven to be most practical and allows for regio- and chemoselective metalation of a wide range of aromatics with sensitive functional groups (CONEt2 , CO2 Me, CN, OCONMe2 ) or halogens (F, Cl, Br, I). The resulting aromatic aluminates, which were characterized by using NMR spectroscopy, were subjected to allylations, acylations, and palladium-catalyzed cross-coupling reactions after transmetalation to zinc. It was shown that the nature of the Zn salt used for transmetalation is crucial. Thus, compared with ZnCl2 (2 equiv), the use of Zn(OPiv)2 (2 equiv; OPiv=pivalate) allows the subsequent quenching reactions to be performed with only a slight excess of electrophile (1.2 equiv) and provides interesting functionalized aromatics in good yields.