Zur Anlagerung des Benzonitriloxids an α,β-ungesättigte Carbonsäureester

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Rearrangement of Free Radicals, XII. ESR Spectroscopic Study of the Ring Opening of the Homobenzvalenyl Radical

Abstraction of an allylic hydrogen atom in homobenzvalene (4) either in solurion by photolyticaßy generated tert-butoxyl radicals or in an adamantane matrix by X-rays produces the homobcnzvalenyl radical (5). which tbennally rearranps · to tbe tropylium ndical (1). In solution tbe activation cnergy for the rate determined step of the reaction sequence was detennined· to be 13.4 ± O.S kcal/mol

α-Diketones in [4+2]Cycloadditions, Reactions of Dimethyl 2,3-Dioxosuccinate with Enol Ethers

Dimethyl 2,3-dioxosuccinate (1) undergoes cycloaddition with enol ethers. Dihydrodioxine derivates, products of [4+2] cycloaddition, are formed with tetraethoxyethylene and E-1,2-dimethoxyethylene. The stereospecificity of the reaction of 1 with E-1,2-dimethoxyethylene suggests a concerted mechanism for this cycloaddition. The polarized double bond of ethyl vinyl ether reacts with 1 to give 4,5-dihydro-2,3-dimethoxycarbonyl-2,3-epoxy-5-ethoxyfuran in a hitherto unknown reaction of 1,2-diketones

Diels-Alder-Reaktion eines elektronenarmen C-Acylimins mit Tetraethoxyethylen

The synthesis of two C-acylimines and their reactivity towards electron rich dienophiles inDiels-Alder reactions is described. A [4+2] cycloadduct is obtained only in one case: from the reaction of a C-acylimine substituted by two methoxycarbonyl groups with tetraethoxyethylene. No [2+2] cycloadducts are observed

Ethoxyacetylene and ethyl vinyl ether, dipolarophiles of opposite regiochemistry in diazomethane cycloadditions

Diazomethane adds to ethoxyacetylene to give a 96 : 4 mixture in favor of 4-ethoxypyrazole (3) which had been identified as the only product in a previous study. This result contrasts the behavior of ethyl vinyl ether which gives 3-ethoxy-1-pyrazoline (2). Transition structures for the four possible regioisomers are determined by MNDO-PM3 calculations. The regioselectivity is explained on the basis of the PM3 calculations and their perturbational analysis using the program PERVAL. Distortions of the dipolarophiles in the transition structures due to closed-shell repulsions lead to FMO interactions which favor the experimental regiochemistry

Light-induced cooperative electron–proton transfer in hydrogen-bonded networks of N,N-diaryl substituted 1,4-bisimines and meso-1,2-diaryl-1,2-ethanediols

The 1:1 cocrystallization of 1,4-diaryl-1,4-bisimines (Ar–CHN–CH2-)2 4–11and substituted meso-1,2-diaryl-1,2-ethanediols 1–3 leads to supramolecular structures in which the diol is hydrogen bonded by one of its hydroxy groups to an imine nitrogen atom of a 1,4-bisimine. The second functionality in each molecule leads to the generation of ladderlike polymeric structures where each molecule of the diol is linked to two molecules of the 1,4-bisimine and vice versa. If the diol carries electron donor groups in the aromatic residue and the 1,4-bisimine correspondingly acceptor groups, then charge transfer interactions are observed. The excited CT complex which corresponds to a radical ion pair is stabilized by migration of a proton of a hydroxy group to the nitrogen atom of an imino group. This is supported by the appearance of a N–H vibration in the IR spectra. The reorganization is also accompanied by changes in the UV/Vis spectra and by the generation of paramagnetism in the crystalline material. The results represent a type of photochromism which has its origin in a light-induced cooperative electron–proton transfer. The photochromism is thermally reversible