Ruthenium-Catalyzed Oxidation of Allyl Alcohols with Intermolecular Hydrogen Transfer: Synthesis of α,β-Unsaturated Carbonyl Compounds

Selectivity Effects of Hydrogen Acceptors and Catalyst Structures in Alcohol Oxidations Using (Cyclopentadienone)iron Tricarbonyl Compounds

Oppenauer-type oxidations are catalyzed by air- and moisture-stable, sustainable, (cyclopentadienone)iron carbonyl compounds, but the substrate scope is limited due to the low reduction potential of acetone, which is the most commonly used hydrogen acceptor. We discovered that furfural, an aldehyde derived from cellulosic biomass, is an effective hydrogen acceptor with this class of catalysts. In general, reactions using furfural as the hydrogen acceptor led to higher isolated yields of ketones and aldehydes compared to those using acetone. Importantly, primary benzylic and allylic alcohols─typically a challenging class of alcohols to oxidize with these catalysts─could be oxidized. The selectivity for primary vs secondary alcohol oxidation with (cyclopentadienone)iron carbonyl catalysts was also explored using acetone and furfural as the hydrogen acceptors. Most of the catalysts tested preferentially oxidized unhindered secondary alcohols, but catalysts with trialkylsilyl groups in the 2- and 5-positions of the cyclopentadienone preferentially oxidized primary alcohols. A combination of substrate scope experiments and kinetic studies concluded that the selectivity with the trialkylsilyl-based catalysts was kinetically derived─primary alcohols were oxidized more quickly than secondary─and the selectivity for secondary alcohol oxidation with the other catalysts arose from the equilibrium-driven nature of the Oppenauer-type oxidation.

Palladium-Catalyzed Oxidative Nonclassical Heck Reaction of Arylhydrazines with Allylic Alcohols via C-N Bond Cleavage: Access to β-Arylated Carbonyl Compounds

An efficient palladium-catalyzed oxidative nonclassical Heck reaction of arylhydrazines with allylic alcohols via C-N bond cleavage has been successfully developed. This method provides a series of β-arylated carbonyl compounds with broad functional group tolerance under base-free, simple, and mild open air reaction conditions. In the reaction, arylhydrazines with the smaller molecular weight of the leaving group were employed as the "green" arylation reagent, which released N₂ and water as the byproducts under air. Mechanistic studies suggested that an aryl radical process and Pd-H complex migration reinsertion were involved. Moreover, the synthesis of the antiarrhythmic drug propafenone was completed with this transformation as the key step.

One-pot synthesis of α,β-unsaturated ketones through sequential alkyne dimerization/hydration reactions using the Hoveyda–Grubbs catalyst

The combination of HG2/PCy3 and CCl3COOH/p-TsOH·H2O through one-pot alkyne dimerization/hydration reactions gave α,β-unsaturated ketones in quantitative yields within 2.5–4 h.

Base-free oxidation of alcohols enabled by nickel(ii)-catalyzed transfer dehydrogenation

An efficient nickel(ii)-catalyzed transfer dehydrogenation oxidation of alcohols is reported that relies on cyclohexanone as the formal oxidant and does not require the use of an external base. The synthetic utility of this protocol is demonstrated via the facile oxidation of structurally complicated natural products.

nBu4NOTf-promoted radical self-hydrogen transferring isomerization under transition metal-free conditions

We report the first allylic isomerization of alcohols catalyzed by ⁿBu₄NOTf generated in situ from tetrabutylammonium triflate and potassium tert-butoxide.

Chemoselective α-Methylenation of Aromatic Ketones Using the NaAuCl4/Selectfluor/DMSO System

Gold-catalyzed chemoselective α-methylenation of aromatic ketones was developed through the use of Selectfluor as a methylenating agent. A variety of useful 1,2-disubstituted propenone derivatives can be prepared in good yields via the present protocol. This reaction features a simple operation, good functional group tolerance, and broad scope of substrates.