Megh Singh

Solvent tuning of diastereoselectivity in dimethyldioxirane epoxidation reactions

Diastereoselectivity in the epoxidation of cyclohex-2-en-1-ol shows a remarkable solvent dependence. In some solvent systems the substrate OH group apparently can provide a cis selectivity through H-bonding.

A convenient high yield synthesis of nitroxides

Abstract Appropriate secondary amines are readily converted to nitroxides by dimethyldioxirane in a rapid, convenient, and essentially quantitative process.

A High Yield One Step Synthesis of Hydroxylamines

Abstract Oxidation of secondary amines with dimethyl-dioxirane gives hydroxylamines in a simple, one step and high yield process.

Stereochemistry in the oxidation of primary amines to nitro compounds by dimethyldioxirane

Abstract Oxidation of the chiral amines, (+) and (−)-isopinocampheylamine, with dimethyldioxirane (1) gives the corresponding nitro compounds with retention of configuration at the amine-bearing carbon atom. When lower amounts of 1 are used in the oxidation the amines give the nitroso dimers as the major products. Treatment of the nitroso dimer from the (−)-amine with additional 1 gave the same nitro compound as obtained from the amine oxidation. To further indicate that no racemization occurs during the amine oxidation we have synthesized the oxime of the nitroso intermediate and shown that it does not tautomerize under the reaction conditions.

The reaction of cyclooctatetraene with dimethyldioxirane

Abstract The reaction of cyclooctatetraene with dimethyldioxirane leads to the formation of four diepoxides, three triepoxides, and two tetraepoxides. The structures of the triepoxides and tetraepoxides were confirmed by x-ray crystallographic analysis.

The reaction of dimethyldioxirane with chrysene: Formation of a trioxide

Abstract Oxidation of chrysene with dimethyldioxirane gives a number of products including the interesting trioxide, chrysene-5,6:4b,10b:11,12-trioxide, 3. The x-ray crystallographic stucture of 3 indicates that it is a non-planar system.

Activation of Pah by Ozone Derived Oxidants: Results Using Fly Ash as Particulate [1]

Abstract The fly ash bound polycyclic aromatic hydrocarbons (PAH), phenanthrene, pyrene, and cyclopenta[cd]pyrene, are converted to arene oxides when exposed to the products of the gas phase reaction of tetramethylethylene and ozone. These same PAH are also converted to the same oxides when treated with dimethyldioxirane vapors while adsorbed on the fly ash. Exposure to ozone alone does not give oxide formation under the same conditions. Several other PAH fail to give oxides when treated with the tetramethylethylene/ozone product stream. The results support the hypothesis that the products of the ozonolysis of alkenes in polluted atmospheres may be responsible for the activation of PAH in these atmospheres.

X-ray Crystal Structures of Some Arene Oxides

Using a recently disclosed modification to the dimethyldioxirane method we have synthesized four arene monooxides and one trioxide in good to excellent yield. The X-ray crystal structures have been determined for all of these compounds. In the case of the chrysene trioxide the X-ray determination reveals that the structure is bent out of the plane.

An ESR study of the disappearance of the paramagnetism of polycrystalline 4,4′-butadiyne-1,4-diyl bis(2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl) (BIPO) at elevated temperatures

Abstract Room temperature ESR studies of polycrystalline samples of 4,4′-butadiyne-1,4-diyl bis(2,2,6,6-tetramethyl-4-hydroxy-piperidin-1-oxyl), BIPO, reveal that the spectral envelopes observed depend upon the purity and crystalline form in which the BIPO exists. The ESR signal intensity observed for samples of BIPO at elevated temperatures decreases with time. Although there is an initial period at which the reaction proceeds at a slower rate, the rate of disappearance of the paramagnetism is first order and within 3 hours less than 3% of the initial paramagnetism remains. As the concentration of the paramagnetic species decreases, the spectral envelope changes from that of a spin-spin exchange narrowed line to that of a magnetically dilute fixed site solid state nitroxide free radical solution.

New Synthetic Metal Precursors: Substituted Tetrathiotetracene and Related Compounds

The electron donor tetrathiotetracene (TTT), Fig. 1, forms charge transfer salts which, at room temperature, possess some of the highest electrical conductivities of any known synthetic metal1. For example, a conductivity of ca 103 S/cm is observed for (TTT)2I3 at room temperature. As the temperature of the complex is decreased, the conductivity increases until ca 35 K, at which point it decreases dramatically2. While not firmly established, it is believed that the latter behavior is the result of a Peierls transition, which allows alternating pairwise interactions to occur between adjacent TTT molecules and cations.