Lanthanide-Catalyzed Oxyfunctionalization of 1,3-Diketones, Acetoacetic Esters, And Malonates by Oxidative C–O Coupling with Malonyl Peroxides

Abstract

The lanthanide-catalyzed oxidative C-O coupling of 1,3-dicarbonyl compounds with diacyl peroxides, specifically the cyclic malonyl peroxides, has been developed. An important feature of this new reaction concerns the advantageous role of the peroxide acting both as oxidant and reagent for C-O coupling. It is shown that lanthanide salts may be used in combination with peroxides for selective oxidative transformations. The vast range of lanthanide salts (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Y) catalyzes oxidative C-O coupling much more efficiently than other used Lewis and Bronsted acids. This oxidative cross-coupling protocol furnishes mono and double C-O coupling products chemo-selectively in high yields with a broad substrate scope. The double C-O coupling products may be hydrolyzed to vicinal tricarbonyl compounds, which are otherwise cumbersome to prepare. Based on the present experimental results, a nucleophilic substitution mechanism is proposed for the C-O coupling process in which the lanthanide metal ion serves as Lewis acid to activate the enol of the 1,3-dicarbonyl substrate. The side reactions-chlorination and hydroxylation of the 1,3-dicarbonyl partners-may be minimized under proper conditions.

Selective Oxidative Coupling of 3H‐Pyrazol‐3‐ones, Isoxazol‐5(2H)‐ones, Pyrazolidine‐3,5‐diones, and Barbituric Acids with Malonyl Peroxides: An Effective C‐O Functionalization

“…According to the Introduction , previous oxidations of such heterocyclic substrates by alternative oxidants – for example peracids [20],[21],[23],[28],[31] – resulted mainly in the hydroxylation of the C−H bond or its further oxidation to the oxo functionality. The remarkable feature of the heterocycles 1–4 is the fact that their oxidative C−O coupling requires no lanthanide catalyst nor any other Brönsted or Lewis acid catalysis, as was reported previously for the 1,3‐dicarbonyl substrates …”

“…Analogous to the mechanism for the oxidative C−O coupling of the 1,3‐dicarbonyl substrates with the malonyl peroxides 5 , we propose Scheme for the oxyfunctionalization of the heterocycles 1–4 , taking 3 H ‐pyrazol‐3‐ones 1 as prototype example.…”

Design of Selenium‐Based Chiral Chemical Probes for Simultaneous Enantio‐ and Chemosensing of Chiral Carboxylic Acids with Remote Stereogenic Centers by NMR Spectroscopy

“…To test this, we chose the formation of chiral carboxylic acids by lanthanide‐catalyzed oxidative C−O coupling of 1,3‐dicarbonyl compounds with diacyl peroxide recently developed by Terent′ev et al. (Scheme ) . After the completion of the reaction, an aliquot of the crude reaction mixture was taken, the solvent was evaporated under reduced pressure, and the residue was derivatized by using the typical protocol discussed above…”

“…Reagents were obtained from Acros and Aldrich and used as supplied (checked by NMR spectroscopy and GC before use). The acids to prepare diastereomers 18 – 24 , 37 , and 38 can be synthesized according to published procedures . The acids to prepare diastereomers 4 , 8 , and 10 were synthesized according to published procedures .…”

Silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with malonyl peroxides in solvent-free conditions

“…Previously we developed an efficient lanthanide-catalyzed oxidative C-O coupling in which one of the reagents, diacyl peroxide, acts both as an O-component for coupling and as the oxidizing agent for C-components -β-dicarbonyl compounds [10,11]. The advantageous feature of the disclosed process is the unusual the catalytic activity of SiO 2 is explained by the influence of acidic Si-OH groups, but complete understanding of the catalytic properties of silica gel and supported catalyst systems based on it, still represents an actual fundamental problem.…”