Benzimidazole condensed ring systems. 2. New synthesis of substituted 1-oxo-1H,5H-pyrido[1,2-a]benzimidazole-4-carbonitriles and related derivatives

The synthesis of some 3-substituted and 2,3-disubstituted-1-oxo-1H,5H-pyrido[1,2-a]benzimidazole-4-carbo-nitriles 5,6 by fusing 1H-benzimidazole-2-acetonitrile 1 with some β-keto esters 2,4 in the presence of ammonium acetate or with ethyl β-aminocrotonate 3 is described. The tricyclic compounds were converted to their N-5 methyl of N-5 ethyl derivatives 8,9. Vilsmeir-Haack formylation of 3-methyl-1-oxo-1H,5H-pyrido[1,2-a]-benzimidazole-4-carbonitrile 5a afforded its 2-formyl derivative 10. Chlorination of 5 and 6 with phosphorus oxychloride yielded the respective 1-chloropyrido[1,2-a]benzimidazole-4-carbonitriles 11,12 which were utilized to prepare the 1-azido, 1-amino, 1-piperidino and 1-methoxy derivatives of the ring system. Compound 11a exhibited strong in vitro activity against S. aureus. Four compounds were screened against P-388 lymphocytic leukemia in mice but were inactive.     

Reaktionen mit β-Aminocrotonsäureester

Zusammenfassung -Aminocrotonsäureester (1) reagiert mit Malonestern (2 a und2 b) im Molverhältnis 21 über das 4-Hydroxy-2-pyridon4 zum 4.7-Dimethyl-2.5-dioxo-5.6-dihydro-2H-pyrano[3.2-c]-pyridin-8-carbonsäureester (5 a). Die Möglichkeit,1 an Stelle von Acetessigester und mit besserem Erfolg im Sinne einerPechmann-Reaktion ohne Katalysator mit phenol. Verbindungen umzusetzen, wird aufgezeigt.

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Syntheses of heterocycles, CLX: Reactions of ethyl -aminocrotonate. A modification of the pechmann reaction

Ethyl -aminocrotonate (1) reacts with the malonates2a and2 b (using a molar ratio of 2: 1)via the 4-hydroxy-2-pyridone4 to give ethyl 4.7-dimethyl-2.5-dioxo-5.6-dihydro-2H-pyrano-[3.2-c]pyridine-8-carboxylate (5 a). It has been shown that1 (without any catalyst) can replace ethyl acetoacetate in thePechmann reaction giving better yields in many cases.

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Zur Synthese mesomerer Pyrimidinbetaine

N.N′-disubstituted amidines react with monosubstituted 2.4.6-trichlorophenyl malonates (2 a-d) yielding mesoionic compounds with a six-membered ring. The 2-aminopyridines1 a-c react in the same way to give the bicyclic mesomeric betaines3 b-g. 3 a is obtained by the action of carbon suboxide (C₃O₂) on1 a.     

Controlled microwave heating in modern organic synthesis

Although fire is now rarely used in synthetic chemistry, it was not until Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied to a reaction vessel in a focused manner. The Bunsen burner was later superseded by the isomantle, oil bath, or hot plate as a source for applying heat to a chemical reaction. In the past few years, heating and driving chemical reactions by microwave energy has been an increasingly popular theme in the scientific community. This nonclassical heating technique is slowly moving from a laboratory curiosity to an established technique that is heavily used in both academia and industry. The efficiency of "microwave flash heating" in dramatically reducing reaction times (from days and hours to minutes and seconds) is just one of the many advantages. This Review highlights recent applications of controlled microwave heating in modern organic synthesis, and discusses some of the underlying phenomena and issues involved.     

The Formation of Thioacylthioketenes by Flash Vacuum Pyrolysis of 1,2-Dithiole Derivatives

Abstract

The formation of thioacylthioketenes has been observed in Flash Vacuum Pyrolysis of various 1,2-dithiole derivatives. In some cases C₃S₂, 1,2-propadiene-1,3-dithione is formed too.     

High-throughput synthesis of N3-acylated dihydropyrimidines combining microwave-assisted synthesis and scavenging techniques

[reaction: see text] The solution-phase synthesis of N3-acylated dihydropyrimidines was achieved utilizing microwave flash heating both in the synthesis (acylation) and purification (scavenging) steps. Quenching times for excess anhydrides using polystyrene or silica-supported diamine sequestration reagents were reduced from several hours to minutes utilizing microwave irradiation. The use of water as sequestration agent, coupled with an efficient solid-phase extraction workup technique allowed the rapid generation of a 20-member library of N3-acylated dihydropyrimidines.