Electrolytes for Li-ion transport – Review

A reaction in organic chemistry that creates either furans, pyrroles, or thiophenes from 1,4-dicarbonyl compounds is called Paal–Knorr synthesis. It is a synthetically valued process for gaining substituted furans, pyrroles and thiophene, common structural components of many and variety of biologically active natural products. It was originally described separately by German chemists Carl Paal and Ludwig Knorr in 1884 as a method for the synthesis of furans, and then has been modified for the synthesis of pyrroles and thiophenes. The Paal–Knorr reaction is relatively versatile and multipurpose. In this reaction, almost all dicarbonyls can be converted to their corresponding heterocycles. The Paal–Knorr originally is considered limited by harsh reaction conditions, such as prolonged heating in acid, which may degrade sensitive functionalities in many potential precursors. However, contemporary approaches allow for much milder conditions by avoiding, heat altogether, including microwave irradiation along with use of environmentally benign catalyst required for cyclizations.

Paal–Knorr Reaction in the Synthesis of Heterocyclic Compounds

A novel multi-component synthesis of highly substituted 1,6-dihydropyrazine-2,3-dicarbonitrile derivatives starting from simple and readily available inputs is described. Thus, simply stirring an ethanol solution of 2,3-diaminomaleonitrile, a ketone, and an isocyanide in the presence of a catalytic amount of p-toluenesulfonic acid provided highly substituted 1,6-dihydropyrazine-2,3-dicarbonitrile derivatives in good to excellent yields at ambient temperature.

A novel isocyanide-based three-component reaction: synthesis of highly substituted 1,6-dihydropyrazine-2,3-dicarbonitrile derivatives.

Acceptor substituted N -heterocyclic carbenes and their Rh(I)complexes: Synthesis, structure and properties

Linstead macrocyclization of dinitrile 1 gave [octakis(dimethylamino)porphyrazinato]magnesium(II) 2 and the seco-porphyrazine 4 from adventitious oxidation. The structure of the latter has been unequivocally established by an X-ray crystallographic study. Alternatively, compound 4 was obtained in high yield from the manganese dioxide-mediated oxidation of the free base porphyrazine 3. This convenient method was further extended to core metalated and unsymmetrical porphyrazines. In crystals of zinc−seco-porphyrazine 11, the molecules exist as face-to-face dimers linked via complexation of the zinc center in one molecule to one of the amide oxygen atoms in the other and vice versa. The cleaved pyrrole ring in seco- and diseco-porphyrazines causes a ∼50−70 nm red-shifted split Q-band in the electronic absorption spectra.

F. J. Weigert

Papers

Hydrogen cyanide chemistry. VIII. New chemistry of diaminomaleonitrile. Heterocyclic synthesis

Hydrogen cyanide chemistry part 8, new chemistry of diaminomaleonitrile