Pyridinones Are Not Antioxidants As Shown by Kinetics of Free Radical Autoxidation, but They Prevent Radical Oxidations Catalyzed by Toxic Heavy Metals

Three 2-methyl-3-hydroxypyridinones, 1-methyl-, <b>1</b>; 1-(4-methoxy)­phenyl-, <b>2</b>; and 1-(4-dimethylamino)­phenyl-, <b>3</b>, were discovered not to possess strong antioxidant properties contrary to literature reports. These pyridinones were not active chain-breaking antioxidants toward peroxyl radicals generated from styrene or methyl oleate initiated by azobis-2-methylpropylnitrile (AIBN) in solution compared to known phenolic antioxidants, 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC) or 2,6-di-<i>tert</i>-butyl-4-methoxyphenyl (DBHA). Pyridinone <b>2</b> exhibited weak antioxidant activity in cumene, <i>k</i>_inh = 1.3 × 10³ M^–1 s^–1, compared to 2,6-di-<i>tert</i>-butyl-4-methylphenol (BHT), <i>k</i>_inh = 4.3 × 10³ M^–1 s^–1. The pyridinones were not active antioxidants during lipid peroxidation initiated by azobis-2-amidinopropane·2HCl (ABAP) in aqueous–lipid dispersions of 0.50 M sodium dodecyl sulfate (SDS) micelles where <b>2</b> did not inhibit peroxidation of methyl oleate at pH 7.0 or 4.0, while BHT exhibited effective suppression of oxygen uptake. In addition, <b>2</b> did not exhibit any cooperative antioxidant effect in combination with Trolox during inhibited peroxidation of linoleic acid in micelles. Pyridinones were effective <i>preventative</i> antioxidants in aqueous–lipid dispersions against reactions initiated by heavy metal ions, notably copper; for example, <b>2</b> blocked peroxidation of linoleic acid initiated by Cu ions in SDS micelles. In particular, both <b>2</b> and <b>3</b> were active in preventing the rapid <i>pro-oxidation</i> effects, “spikes”, of very rapid oxygen uptake when phenolic antioxidants PMHC or Trolox were added to peroxidations initiated by Cu²⁺. A proposal is given to account for such pro-oxidant effects

Strategic Trimethylsilyldiazomethane Insertion into pinB–SR Followed by Selective Alkylations

The insertion of the diazo derivative Me₃SiCHN₂ into pinB–SR σ bonds (R = Ph, Tol, Bn) allows a direct synthesis of multisubstituted H–C­(SR)­(Bpin)­(SiMe₃) compounds. Consecutive base-assisted transformations of HC­(S)­(B) (Si) systems lead to deborylative alkylations, Sommelet–Haüser rearrangements, and deprotoalkylations. Intramolecular cyclizations can be selectively performed either via desilylative or deborylative manifolds by fine-tuning the base employed

Palladium-Catalyzed Suzuki–Miyaura Cross-Couplings with 2‑Diethylphosphonato-Substituted Aryl- and Naphthylboronate Esters as the Nucleophilic Partner: A Complementary Approach to the Synthesis of Biaryl Monophosphonates

This paper reports the first examples of Suzuki–Miyaura cross-couplings involving aryl- and naphthylphosphonate-based boronate esters as the nucleophilic partner. A systematic comparison of the performance of biaryl-like KITPHOS- and XPHOS-based systems revealed that, between them, an electronically and sterically diverse range of substrates can be coupled with remarkable efficiency to afford high yields of the corresponding biaryl and heterobiaryl monophosphonates. The use of an aryl- and naphthylphosphonate-based boronate ester as the coupling partner presents an alternative and potentially complementary pathway to existing couplings in which the aryl- or naphthylphosphonate unit is typically introduced as the electrophile. The potential advantages associated with the use of this new class of coupling partner were clearly demonstrated by the palladium-catalyzed reaction between diethyl [2-(4,4,5,5-tetra­methyl-1,3,2-dioxa­borolan-2-yl)­phenyl]­phosphonate and 1-bromo-2-methoxy­naphthalene that gave the corresponding biaryl monophosphonate in 56% yield, a marked improvement on the 6% yield obtained from the reaction between 2-methoxy-1-naphthyl­boronic acid and diethyl (2-bromo­phenyl)­phosphonate with the same catalyst under the same conditions. The potential utility of this new coupling combination was demonstrated by reducing one of the products, 2-methoxy-1-(2′-diethoxy­phosphoryl­phenyl)­naphthylene, to the corresponding primary phosphine, which was subsequently converted into a diastereoisomeric mixture of the <i>R</i>,<i>R</i>-hexane-2,5-diol-derived phospholane in reasonable yield

Thioboration of α,β-Unsaturated Ketones and Aldehydes toward the Synthesis of β‑Sulfido Carbonyl Compounds

Herein a direct β-sulfido carbonyl compound synthesis by the easy activation of RS−Bpin reagents with α,β-unsaturated ketones and aldehydes is reported. This convenient methodology can be performed at room temperature with no other additives. The key point of this reactivity is based on the Lewis acidic properties of the boryl unit of the RS−Bpin reagent interacting with the CO oxygen. Consequently, the SR unit becomes more nucleophilic and promotes the 1,4- versus the 1,2-addition, as a function of the involved substrate. The thioborated products can be further transformed into β-sulfido carbonyl compounds by addition of MeOH