Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose: Novel 1,2-Addition of a Dienolate to a Chiral Ketone

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose:  Novel 1,2-Addition of a Dienolate to a Chiral Keton

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose: Novel 1,2-Addition of a Dienolate to a Chiral Ketone

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose:  Novel 1,2-Addition of a Dienolate to a Chiral Keton

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose: Novel 1,2-Addition of a Dienolate to a Chiral Ketone

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose:  Novel 1,2-Addition of a Dienolate to a Chiral Keton

Metal-Free, One-Pot, Sequential Protocol for Transforming α,β-Epoxy Ketones to β‑Hydroxy Ketones and α‑Methylene Ketones

A new sequential, one-pot protocol for transforming 1,3-disubstituted 2,3-epoxy ketones to β-hydroxy ketones and α-methylene ketones has been developed. Reaction of epoxy ketones with boron trifluoride etherate (BF₃·OEt₂) generates the cationic intermediates by regioselective epoxide ring opening and an acyl shift. Then, a treatment of these cations with 2-aryl-1,3-dimethylbenzimidazolines (DMBIH) results in formation of 1,2-disubstituted 3-hydroxy ketones. DMBIH serves as a hydride donor in the second step of this process. Finally, the β-hydroxy ketones can be converted to 1,2-disubstituted 2-methylene ketones by treatment with methanesulfonic acid or a combination of methanesulfonyl chloride and triethylamine. Importantly, the sequential steps involved in formation of the α-methylene ketone products can be carried out in one pot

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose: Novel 1,2-Addition of a Dienolate to a Chiral Ketone

Synthesis of the Chiral CD Rings of Paclitaxel from 2-Deoxy-d-ribose:  Novel 1,2-Addition of a Dienolate to a Chiral Keton

Solvent-Dependent Reaction Pathways Operating in Copper(II) Tetrafluoroborate Promoted Oxidative Ring-Opening Reactions of Cyclopropyl Silyl Ethers

Oxidative ring-opening reactions of benzene-fused bicyclic cyclopropyl silyl ethers, promoted by copper­(II) tetrafluoroborate, were investigated. The regioselectivity of cyclopropane ring-opening as well as product distributions were found to be highly dependent on the nature of the solvent. In alcohols, dimeric substances arising from external bond cleavage are major products. Radical rearrangement products are also formed in solvents such as ether and ethyl acetate. On the contrary, nucleophile addition to carbocation intermediates, generated by internal bond cleavage, occurs mainly in reactions taking place in acetonitrile. It is proposed that the observed solvent effects that govern the reaction pathways followed are a consequence of varying solvation of copper intermediates, which governs their reactivity and redox properties. In addition, the influence of counteranions of the copper salts, organonitriles, cyclic dienes, and substrate structures on the pathways followed in these reactions was also examined

A Photocatalytic System Composed of Benzimidazolium Aryloxide and Tetramethylpiperidine 1‑Oxyl to Promote Desulfonylative α‑Oxyamination Reactions of α‑Sulfonylketones

A new photocatalytic system was developed for carrying out desulfonylative α-oxyamination reactions of α-sulfonylketones in which α-ketoalkyl radicals are generated. The catalytic system is composed of benzimidazolium aryloxide betaines (BI+–ArO–), serving as visible light-absorbing electron donor photocatalysts, and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), playing dual roles as an electron donor for catalyst recycling and a reagent to capture the generated radical intermediates. Information about the detailed nature of BI+–ArO– and the photocatalytic processes with TEMPO was gained using absorption spectroscopy, electrochemical measurements, and density functional theory calculations

Triarylamine-Substituted Benzimidazoliums as Electron Donor–Acceptor Dyad-Type Photocatalysts for Reductive Organic Transformations

Triarylamine-substituted benzimidazoliums (BI+–PhNAr2), new electron donor–acceptor dyad molecules, were synthesized. Their photocatalytic properties for reductive organic transformations were explored using absorption and fluorescence spectroscopy, redox potential determinations, density functional theory calculations, transient absorption spectroscopy, and reduction reactions of selected substrates. The results show that irradiation of BI+–PhNAr2 promotes photoinduced intramolecular electron transfer to form a long-lived (∼300 μs) charge shifted state (BI•–PhN•+Ar2). In the pathway for photocatalysis of reduction reactions of substrates, BI•–PhN•+Ar2 is subsequently transformed to the neutral benzimidazolyl radical (BI•–PhNAr2) by single-electron transfer from the donor 1,3-dimethyl-2-phenylbenzimidazoline (BIH–Ph) serving as a cooperative agent. Among the benzimidazoliums explored, the bromo-substituted analogue BI+–PhN­(C6H4Br-p)2 in conjunction with BIH–Ph demonstrates the most consistent catalytic performance

Correction to “Triarylamine-Substituted Benzimidazoliums as Electron Donor–Acceptor Dyad-Type Photocatalysts for Reductive Organic Transformations”

Correction to “Triarylamine-Substituted Benzimidazoliums as Electron Donor–Acceptor Dyad-Type Photocatalysts for Reductive Organic Transformations

Selective Synthesis of [2]- and [3]Catenane Tuned by Ring Size and Concentration

The syntheses of [2]- and [3]­catenanes by olefin metathesis and oxidative acetylide coupling have been studied in detail. Pseudorotaxanes that were obtained by mixing crown ether and ammonium salts containing two terminal reactive end-groups were converted to [2]- and [3]­catenane. Their yields were influenced not only by the chain length of the ammonium salts but also by the concentration of the crown ether and the ammonium salts. The strain energies of [2]­catenane were responsible for the formation of [2]­catenane