Selective Synthesis of Cyclic Peroxides from Triketones and H₂O₂

A method for the assembly of tricyclic structures containing the peroxide, monoperoxyacetal, and acetal moieties was developed based on the acid-catalyzed reaction of β,δ-triketones with H₂O₂. Tricyclic compounds are formed selectively in yields from 39% to 90% by the reactions with the use of large amounts of strong acids, such as H₂SO₄, HClO₄, or HBF₄, which act both as the catalyst and as the co-solvent. The reaction is unusual in that, despite the diversity of possible peroxidation pathways giving cyclic compounds and oligomers, the reaction proceeds with high selectivity and produces tricyclic peroxides via the monoperoxidation of the carbonyl groups in the β-positions and the transformation of the δ-carbonyl group into the acetal one. The syntheses are scaled up to tens of grams, and the resulting peroxides can be easily isolated from the reaction mixture

Selective Synthesis of Cyclic Peroxides from Triketones and H₂O₂

A method for the assembly of tricyclic structures containing the peroxide, monoperoxyacetal, and acetal moieties was developed based on the acid-catalyzed reaction of β,δ-triketones with H₂O₂. Tricyclic compounds are formed selectively in yields from 39% to 90% by the reactions with the use of large amounts of strong acids, such as H₂SO₄, HClO₄, or HBF₄, which act both as the catalyst and as the co-solvent. The reaction is unusual in that, despite the diversity of possible peroxidation pathways giving cyclic compounds and oligomers, the reaction proceeds with high selectivity and produces tricyclic peroxides via the monoperoxidation of the carbonyl groups in the β-positions and the transformation of the δ-carbonyl group into the acetal one. The syntheses are scaled up to tens of grams, and the resulting peroxides can be easily isolated from the reaction mixture

Selective Synthesis of Cyclic Peroxides from Triketones and H₂O₂

A method for the assembly of tricyclic structures containing the peroxide, monoperoxyacetal, and acetal moieties was developed based on the acid-catalyzed reaction of β,δ-triketones with H₂O₂. Tricyclic compounds are formed selectively in yields from 39% to 90% by the reactions with the use of large amounts of strong acids, such as H₂SO₄, HClO₄, or HBF₄, which act both as the catalyst and as the co-solvent. The reaction is unusual in that, despite the diversity of possible peroxidation pathways giving cyclic compounds and oligomers, the reaction proceeds with high selectivity and produces tricyclic peroxides via the monoperoxidation of the carbonyl groups in the β-positions and the transformation of the δ-carbonyl group into the acetal one. The syntheses are scaled up to tens of grams, and the resulting peroxides can be easily isolated from the reaction mixture

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

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

Reduction of Organosilicon Peroxides: Ring Contraction and Cyclodimerization

The reduction of 1,2,7,8-tetraoxa-3,6-disilonanes is accompanied by the selective transformation of two SiOOC moieties into SiOC moieties, resulting in contraction of the nine-membered ring bis-peroxide to a previously unknown class of seven-membered-ring acetals, 1,6-dioxa-2,5-disilepanes. The reduction of six-membered cyclic peroxide proceeds differently and affords four- and eight-membered rings. As a result, silyl ethers of <i>gem</i>-diols, which do not exist in the free form, are produced

Reduction of Organosilicon Peroxides: Ring Contraction and Cyclodimerization

The reduction of 1,2,7,8-tetraoxa-3,6-disilonanes is accompanied by the selective transformation of two SiOOC moieties into SiOC moieties, resulting in contraction of the nine-membered ring bis-peroxide to a previously unknown class of seven-membered-ring acetals, 1,6-dioxa-2,5-disilepanes. The reduction of six-membered cyclic peroxide proceeds differently and affords four- and eight-membered rings. As a result, silyl ethers of <i>gem</i>-diols, which do not exist in the free form, are produced

Well-Known Mediators of Selective Oxidation with Unknown Electronic Structure: Metal-Free Generation and EPR Study of Imide‑<i>N</i>‑oxyl Radicals

Nitroxyl radicals are widely used in chemistry, materials sciences, and biology. Imide-<i>N</i>-oxyl radicals are subclass of unique nitroxyl radicals that proved to be useful catalysts and mediators of selective oxidation and CH-functionalization. An efficient metal-free method was developed for the generation of imide-<i>N</i>-oxyl radicals from <i>N</i>-hydroxyimides at room temperature by the reaction with (diacetoxyiodo)­benzene. The method allows for the production of high concentrations of free radicals and provides high resolution of their EPR spectra exhibiting the superhyperfine structure from benzene ring protons distant from the radical center. An analysis of the spectra shows that, regardless of the electronic effects of the substituents in the benzene ring, the superhyperfine coupling constant of an unpaired electron with the distant protons at positions 4 and 5 of the aromatic system is substantially greater than that with the protons at positions 3 and 6 that are closer to the <i>N</i>-oxyl radical center. This is indicative of an unusual character of the spin density distribution of the unpaired electron in substituted phthalimide-<i>N</i>-oxyl radicals. Understanding of the nature of the electron density distribution in imide-<i>N</i>-oxyl radicals may be useful for the development of commercial mediators of oxidation based on <i>N</i>-hydroxyimides

Ozone-Free Synthesis of Ozonides: Assembling Bicyclic Structures from 1,5-Diketones and Hydrogen Peroxide

Reactions of 1,5-diketones with H₂O₂ open an ozone-free approach to ozonides. Bridged ozonides are formed readily at room temperature in the presence of strong Brønsted or Lewis acids such as H₂SO₄, <i>p</i>-TsOH, HBF₄, or BF₃·Et₂O. The expected bridged tetraoxanes, the products of double H₂O₂ addition, were not detected. This procedure is readily scalable to produce gram quantities of the ozonides. Bridged ozonides are stable and can be useful as building blocks for bioconjugation and further synthetic transformations. Although less stabilized by anomeric interactions than bis-peroxides, ozonides have an intrinsic advantage of having only one weak O–O bond. The role of the synergetic framework of anomeric effects in bis-peroxides is to overcome this intrinsic disadvantage. As the computational data have shown, this is only possible when all anomeric effects in bis-peroxides are activated to their fullest degree. Consequently, the cyclization selectivity is determined by the length of the bridge between the two carbonyl groups of the diketone. The generally large thermodynamic preference for the formation of cyclic bis-peroxides disappears when 1,5-diketones are used as the bis-cyclization precursors. Stereoelectronic analysis suggests that the reason for the bis-peroxide absence is the selective deactivation of anomeric effects in a [3.2.2]­tetraoxanonane skeleton by a structural distortion imposed on the tetraoxacyclohexane subunit by the three-carbon bridge

Ozone-Free Synthesis of Ozonides: Assembling Bicyclic Structures from 1,5-Diketones and Hydrogen Peroxide

Reactions of 1,5-diketones with H₂O₂ open an ozone-free approach to ozonides. Bridged ozonides are formed readily at room temperature in the presence of strong Brønsted or Lewis acids such as H₂SO₄, <i>p</i>-TsOH, HBF₄, or BF₃·Et₂O. The expected bridged tetraoxanes, the products of double H₂O₂ addition, were not detected. This procedure is readily scalable to produce gram quantities of the ozonides. Bridged ozonides are stable and can be useful as building blocks for bioconjugation and further synthetic transformations. Although less stabilized by anomeric interactions than bis-peroxides, ozonides have an intrinsic advantage of having only one weak O–O bond. The role of the synergetic framework of anomeric effects in bis-peroxides is to overcome this intrinsic disadvantage. As the computational data have shown, this is only possible when all anomeric effects in bis-peroxides are activated to their fullest degree. Consequently, the cyclization selectivity is determined by the length of the bridge between the two carbonyl groups of the diketone. The generally large thermodynamic preference for the formation of cyclic bis-peroxides disappears when 1,5-diketones are used as the bis-cyclization precursors. Stereoelectronic analysis suggests that the reason for the bis-peroxide absence is the selective deactivation of anomeric effects in a [3.2.2]­tetraoxanonane skeleton by a structural distortion imposed on the tetraoxacyclohexane subunit by the three-carbon bridge

Ozone-Free Synthesis of Ozonides: Assembling Bicyclic Structures from 1,5-Diketones and Hydrogen Peroxide

Reactions of 1,5-diketones with H₂O₂ open an ozone-free approach to ozonides. Bridged ozonides are formed readily at room temperature in the presence of strong Brønsted or Lewis acids such as H₂SO₄, <i>p</i>-TsOH, HBF₄, or BF₃·Et₂O. The expected bridged tetraoxanes, the products of double H₂O₂ addition, were not detected. This procedure is readily scalable to produce gram quantities of the ozonides. Bridged ozonides are stable and can be useful as building blocks for bioconjugation and further synthetic transformations. Although less stabilized by anomeric interactions than bis-peroxides, ozonides have an intrinsic advantage of having only one weak O–O bond. The role of the synergetic framework of anomeric effects in bis-peroxides is to overcome this intrinsic disadvantage. As the computational data have shown, this is only possible when all anomeric effects in bis-peroxides are activated to their fullest degree. Consequently, the cyclization selectivity is determined by the length of the bridge between the two carbonyl groups of the diketone. The generally large thermodynamic preference for the formation of cyclic bis-peroxides disappears when 1,5-diketones are used as the bis-cyclization precursors. Stereoelectronic analysis suggests that the reason for the bis-peroxide absence is the selective deactivation of anomeric effects in a [3.2.2]­tetraoxanonane skeleton by a structural distortion imposed on the tetraoxacyclohexane subunit by the three-carbon bridge