Cycloadditionen mit Azabenzolen, VIII¹⁾ Reaktionen von Dimethylamino‐ und Methoxypyrimidinen mit Acetylendicarbonsäure‐dimethylester

Abstract

Die Pyrimidine 2a -2i reagieren rnit Acetylendicarbonsaure-dimethylester (1) in siedendem Dimethylformamid uber eine [4 + 2]-Cycloaddition zu den Pyridinderivaten 4a-4e, von denen sich 4 a und 4d mit 1 zu 3-Dimethylaminobenzo1-1,2,4,5-tetracarbonsaure-tetramethylester (5) weiter umsetzen. Cycloaddition Reactions with Azabenzenes, VIII1). -Reactions of Dimethylamino-and Methoxypyrimidines with Dimethyl AcetylenedicarboxylateThe pyrimidines 2a-2i react with dimethyl acetylenedicarboxylate (1) in boiling dimethylformamide by a [4 + 2]-cycloaddition reaction, forming the pyridines 4a-4e. Compounds 4 a and 4d react with 1 giving tetramethyl 3-dimethylaminobenzene-I ,2,4,5-tetracarboxylate (5).In den letzten Jahren konnte in einer Reihe von Untersuchungen gezeigt werden, da13 Azabenzole, wie 1,2,4,5-TetrazineZ), 1,2,4-Triazine3), 1,3,5-Triazine4), Pyridazines), Pyrazines) und Pyrimidine') rnit elektronenreichen Doppel-und Dreifachbindungen in einer Diels-Alder-Reaktion rnit inversem Elektronenbedarf reagieren. Dabei wurde gefunden, dab elektronenziehende Substituenten das heterocyclische System aktivieren.Es stellte sich nun die Frage, ob es gelingt, in einem Azabenzolsystem durch Einfiihrung elektronenspendender Substituenten die Elektronendichte so zu erhohen, da13 es schliel3lich rnit elektronenarrnen Dienophilen, wie Acetylendicarbonsaure-dimethylester (l), in einer [4 + 21-Cycloaddition reagiert. Bei einer derartigen Reaktion hatten wir es rnit einem elektrophilenAngriff des Dienophils amn-System des heterocyclischen *) Korrespondenz bitte an diesen Autor richten. 1 ) VII. Mitteilung: H.

Isotopic Exchange of Hydrogen at C‐5 in Pyrimidine Derivatives: Tautomers with an sp3‐Hybridised C‐5 Carbon Atom

“…The preparation of 2 was carried out according to the method described in the literature. [37] The structures and purity of all the pyrimidine derivatives studied were proved by 1 H and 13 C NMR spectroscopy by using a Bruker Avance II 500 instrument (see the Supporting Information). The prepared samples were analysed by using an Agilent 6890N gas chromatograph (Santa Clara, CA, USA) coupled to a 5975B quadrupole mass spectrometer and equipped with a fused silica capillary column (HP-5ms, 30 mϫ 0.25 mm, 0.25 µm, Agilent).…”

Kost-Sagitullin Rearrangement and Other Isomerization Recyclizations of Pyrimidines. (Review)

“…Thus, 1,4,6-trimethylpyrimidinium iodide (18) is readily hydrolyzed when heated with an aqueous solution of alkali, forming acetylacetone. The action of an aqueous solution of ammonia led to N-demethylation with the formation of 4,6-dimethylpyrimidine (19), while an aqueous solution of methylamine gave a mixture of amines 20 and 21. Reaction with hydrazine also did not lead to the expected Kost-Sagitullin rearrangement, and 3,5-dimethylpyrazole was isolated [5,66] According to the presented examples, the first stage in the recyclization of the pyrimidines takes place normally; ring opening occurs, but degradation is then usually observed.…”

Aminopyrimidines as Electron-Rich Azadienes: Extension of the Synthetic Potential of Hetero Diels-Alder Reactions under Acidic Conditions

“…To prove the applicability of this strategy to fully aromatic pyrimidines, derivative 8 was used as the heterodiene. It was reported by Neunhoeffer et al 13 that the reaction of 8 with DMAD in amine-free dimethylformamide at 150°C yielded the dicarbomethoxypyrimidine derivative 9 as the main product, together with minor amounts of the tetracarbomethoxybenzene derivative 10 (the formation of these products was interpreted as the result of successive HDA/RDA processes from 8). However, when 8 and DMAD were reacted in dioxane at 85°C, only traces of compound 9 were formed, while the main product was the pyrrolo [3,4-c]pyridine derivative 11, together with minor quantities of 10, and two new products 12 and 13 (Scheme 3).…”

“…8 In contrast, the b-glucosides 3c and 3d did not epimerize under the same conditions. All new isolated compounds were fully characterized by spectroscopic methods (IR, UV-Vis, MS, 1 H-and 13 C NMR) and elemental analysis. Especially helpful in the structural assignment of compounds 3 was the X-ray diffraction analysis performed on single crystals of 3d.…”