Copper‐Catalyzed Direct Arylselenation of Anilines by CH Bond Cleavage

The Barton-McCombie deoxygenation is one of the most important transformations in the toolbox of organic chemists which has been the subject of a number of methodological developments. In this study, we report a photocatalyzed redox deoxygenation of secondary and tertiary alcohols from thiocarbamate precursors under visible light activation. The iridium complex Ir(ppy)(3) proved to be the most efficient catalyst in the presence of Hunig's base as sacrifial electron donor. A mechanistic investigation is presented based on fluorescence quenching experiments and cyclic voltammetry.

Visible Light Photocatalytic Reduction of O-Thiocarbamates: Development of a Tin-Free Barton–McCombie Deoxygenation Reaction

The challenging hypothesis of a “biphilic” (i.e., electrophilic vs nucleophilic) character for dioxirane reactivity, which envisages that electron-poor alkenes are attacked by dioxiranes in a nucleophilic fashion, could not be sustained experimentally. Rate data, which estimate Hammett “rho” values for the epoxidation of 3- or 4-substituted cinnamonitriles X·PhCHCHCN, unequivocally allow one to establish that dioxiranes epoxidize electrophilically even alkenes carrying electron-withdrawing groups. The greater propensity of methyl(trifluoromethyl)dioxirane TFDO (1b) to act as an electrophilic oxidant with respect to dimethyldioxirane DDO (1a) parallels the cathode reduction potentials for the two dioxiranes, as measured by cyclic voltammetry. A simple FMO approach for alkene epoxidation is helpful to conceive a likely rationale for the greater oxidizing power of TFDO as compared to DDO.

Concerning the reactivity of dioxiranes. Observations from experiments and theory.

Simple cleavage of diorganyl diselenides with NaBH4/PEG-400 and direct Michael addition to electron-deficient alkenes

The aldol reaction of β-allenoate with use of a commercial THF solution of tetrabutylammonium fluoride (TBAF) yielded polyfunctionalized (2E,4E)-4-carbinol alkadienoate—a valuable building block—in highly regio- and stereoselective fashion.

TBAF-Mediated Aldol Reaction of β-Allenoates: Regio- and Stereoselective Synthesis of (2E,4E)-4-Carbinol Alkadienoates

Several different approaches to the A-ring functionalization of an advanced, highly functionalized diosphenol precursor to Taxol are described. The first phase of the undertaking consists of an assessment of those reagents conducive to reaction at the enolic oxygen (silylation, methylation, allylation, and acylation). Transformations involving an alternative attack at the enol carbon center (bromination, selenation) have also been defined. Sodium borohydride reduction operates from the beta-face of C-14 as long as the C-1 hydroxyl is not protected so as to offer steric exclusion. Complications associated with various aspects of these methodological undertakings are addressed. The most advanced oxygenation achievements were realized by way of a noteworthy sequence involving epoxidation of the O-methyl ether, methanolysis under mildly acidic conditions, and regioselective oxidation of diol 38 to give 39.

Diosphenol-based approach to the a-ring functionalization of advanced Taxol precursors.

Oxidative cleavage of p-methoxybenzyl ethers with methyl(trifluoromethyl)dioxirane.

[543-75-9] C4H6O2 (MW 86.09)





InChI = 1S/C4H6O2/c1-2-6-4-3-5-1/h1-2H,3-4H2



InChIKey = HIZVCIIORGCREW-UHFFFAOYSA-N



(used to introduce carbonyl groups with varying degrees of oxygenation; Diels–Alder, [2 + 2] cycloaddition, and enol ether addition substrate; alcohol protecting group)



Alternate Name: 2,3-dihydro-[1,4]-dioxine, dihydro-[1,4]-dioxin, 2,3-dihydrodioxine.



Physical Data: bp 94 °C; d 1.0836 g cm−3 (20 °C).



Solubility: soluble in organic solvents; insoluble in H2O.



Analysis of Reagent Purity: 1H NMR (500 MHz, CDCl3) δ 5.89 (s, 2H), 4.00 (s, 4H); 13C NMR (125 MHz, CDCl3) ppm 126.7 (2C), 64.4 (2C).1



Preparative Methods: not commercially available. First identified in 1935,2 1,4-dioxene can be prepared through four reaction pathways. Photochlorination of p-dioxane followed by reductive dehalogenation using magnesium and iodine gives 1,4-dioxene after distillation.3 It has also been prepared by heating diethylene glycol at 230–250 °C in the presence of copper chromite and potassium hydrogen sulfate.4 Pyrolysis of the photoadduct of 9,10-phenanthrenequinone and p-dioxane at 230–250 °C gives 1,4-dioxene after purification by distillation.5 Finally, pyrolysis of 2-acetoxy-1,4-dioxane at 450 °C, which is formed from the reaction between lead(IV) acetate and p-dioxane, gives pure 1,4-dioxene.1



Handling, Storage, and Precautions: 1,4-dioxene can be stored for a significant period of time (years) if kept in a freezer. Storage in the presence of acids should be avoided as conversion to 2-hydroxydioxane, which is in equilibrium with 5-hydroxy-3-oxapentanal, occurs.6

1,4‐Dioxene

[reaction: see text] The ability of methyl(trifluoromethyl)dioxirane to cleave p-methoxylbenzyl ethers oxidatively in the presence of various additional functional groups has been investigated. These reactions, performed in aqueous acetonitrile, transform a reasonably robust aryl substituent into a dienyl aldehydo ester. The originally generated E,Z-isomer undergoes slow conversion to the more stable E,E-form at 20 degrees C.

Oxidative Cleavage of p-Methoxybenzyl Ethers with Methyl(trifluoromethyl)dioxirane.

Development of a Process to a 4-Arylated 2-Methylisoquinolin-1(2H)-one for the Treatment of Solid Tumors: Lessons in Ortho-Bromination, Selective Solubility, Pd Deactivation, and Form Control

Matthew M. Kreilein

Papers

Diosphenol-based approach to the a-ring functionalization of advanced Taxol precursors.

Oxidative cleavage of p-methoxybenzyl ethers with methyl(trifluoromethyl)dioxirane.

1,4‐Dioxene

Oxidative Cleavage of p-Methoxybenzyl Ethers with Methyl(trifluoromethyl)dioxirane.

Development of a Process to a 4-Arylated 2-Methylisoquinolin-1(2H)-one for the Treatment of Solid Tumors: Lessons in Ortho-Bromination, Selective Solubility, Pd Deactivation, and Form Control