Rhodium-Catalyzed Asymmetric Conjugate Addition of Organoboronic Acids to Carbonyl-Activated Alkenyl Azaarenes

Chiral Binaphthol-Catalyzed Enantioselective Conjugate Addition of Alkenyl and Arylboronic Acids to α,β-Unsaturated Cyclic N-Sulfonyl Ketimines

The chiral binaphthol-catalyzed enantioselective conjugate addition of alkenylboronic acids and heteroarylboronic acids to cyclic N-sulfonyl ketimines is reported, providing the 1,4-addition products in high yields and moderate to excellent enantioselectivities (up to >99% ee). This mild, scalable catalytic system exhibits high efficiency and broad substrate scopes. Additionally, arylboronic acids were viable nucleophiles under more forcing conditions.

Redox-neutral and metal-free synthesis of 3-(arylmethyl)chroman-4-ones via visible-light-driven alkene acylarylation

A metal- and aldehyde-free visible-light-driven photoredox-neutral alkene acylarylation with readily available cyanoarenes is described. A variety of 3-(arylmethyl)chroman-4-ones (i.e., homoisoflavonoids) and analogs are efficiently synthesized with good functional group tolerance. This mild protocol relies on a phosphoranyl radical-mediated acyl radical-initiated cyclization and selective radical-radical coupling sequence, and is also further highlighted by subsequent derivatization to chromone and 2H-chromene as well as its application in the three-component alkene acylarylation.

Enantioselective Conjugate Addition of Alkenyl Trifluoroborates to Alkenyl-Substituted Benzimidazoles Catalyzed by Chiral Binaphthols

The enantioselective organocatalytic conjugate alkenylation of β-substituted alkenyl benzimidazoles afforded β-stereogenic 2-alkyl benzimidazole derivatives in excellent enantioselectivities. Chiral binaphthols were effective catalysts for promoting the nucleophilic addition of bench-stable alkenyl trifluoroborate salts under mild conditions, expanding their applications by utilizing C=N-containing azaarenes as activating groups. The synthetic utility of this strategy is demonstrated by conversions into several useful enantiomerically enriched benzimidazole building blocks.

Enantioselective Conjugate Addition of Boronic Acids to α,β-Unsaturated 2-Acyl Imidazoles Catalyzed by Chiral Diols

Herein, we report the enantioselective conjugate addition of organic boronic acids to α,β-unsaturated 2-acyl imidazoles using (R)-3,3'-I₂-BINOL as the catalyst. The catalytic system shows high efficiency and tolerance to alkenylboronic acids and heteroarylboronic acids. The corresponding Michael addition products were obtained in moderate to excellent yields and with moderate to excellent enantioselectivities (up to 97% ee). A gram-scale reaction was also conducted, and the desired product was obtained in high yield with no erosion in enantioselectivity. Finally, the synthetic utility of the methodology was demonstrated by transforming the 2-acyl imidazole moiety to the corresponding aldehyde, carboxylic acid, ester, and amide derivatives.

Chiral dihydroxytetraphenylene-catalyzed enantioselective conjugate addition of boronic acids to β-enaminones

An efficient (S)-2,15-Cl2-DHTP-catalyzed enantioselective conjugate addition of organic boronic acids to β-enaminones has been developed.

Crown Ether-Derived Chiral BINOL: Enantioselective Michael Addition of Alkenyl Boronic Acids to α,β-Unsaturated Ketones

A new class of aza-crown ether-derived chiral BINOL catalysts were designed, synthesized, and applied in the asymmetric Michael addition of alkenylboronic acids to α,β-unsaturated ketones. It was found that introducing aza-crown ethers to the BINOL catalyst could achieve apparently higher enantioselectivity than a similar BINOL catalyst without aza-crown ethers did, although the host-guest complexation of alkali ions by the aza-crown ethers could not further improve the catalysis effectiveness. Under mediation of the aza-crown ether-derived chiral BINOL and in the presence of a magnesium salt, an array of chiral γ,δ-unsaturated ketones were furnished in good enantioselectivities (81-95% ees).

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.

Rate Dependence on Inductive and Resonance Effects for the Organocatalyzed Enantioselective Conjugate Addition of Alkenyl and Alkynyl Boronic Acids to β-Indolyl Enones and β-Pyrrolyl Enones

Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates.

A rhodium-catalysed conjugate addition/cyclization cascade for the asymmetric synthesis of 2-amino-4H-chromenes

The enantioselective synthesis of 2-amino-4H-chromenes via the cascade rhodium-catalysed conjugate addition/hetero Thorpe-Ziegler reaction is reported. Moderate to good yields (up to 98%) and high enantioselectivities (up to 92% ee) were obtained with a chiral diene-coordinated rhodium complex as the catalyst. This protocol remedies the methodological deficiency in the asymmetric synthesis of 4-aryl 2-amino-4H-chromenes.

New sp3 diphosphine-based rhodium catalysts for the asymmetric conjugate addition of aryl boronic acids to 3-azaarylpropenones

The new diphosphine (R,R)-EPHOS featuring a stereogenic sp3 carbon combined with a C2 axial chirality was applied to the Rh-catalyzed asymmetric 1,4 addition of aryl boronic acids to 3-azaarylpropenones, affording the product with e.e. up to 94%.

Asymmetric double-conjugate addition of alkenylboronic acids to dienones catalyzed by chiral diols

An efficient asymmetric double-conjugate addition of organic boronic acids to dienones catalyzed by chiral 3,3′-disubstituted-BINOLs or hydroxytetraphenylenes has been developed.

Exploring the copper binding ability of Mets7 hCtr-1 protein domain and His7 derivative: An insight in Michael addition catalysis

Mets7 is a methionine-rich motif present in hCtr-1 transporter that is involved in copper cellular trafficking. Its ability to bind Cu(I) was recently exploited to develop metallopeptide catalysts for Henry condensation. Here, the catalytic activity of Mets7-Cu(I) complex in Michael addition reactions has been evaluated. Furthermore, His7 peptide, in which Met residues have been substituted with His ones, was also prepared. This substitution allowed His7 to coordinate Cu (II), with the obtainment of a stable turn conformation as evicted by CD experiments. His7-Cu (II) proved also to be a better catalyst than Mets7-Cu(I) in the addition reaction. In particular, when the substrate was the (E)-1-phenyl-3-(pyridin-2-yl)prop-2-en-1-one, a conversion of 71% and a significative 58% of e.e. was observed.