Heinrich Wamhoff

Uracils : versatile starting materials in heterocyclic synthesis

Publisher Summary This chapter provides a brief review on uracil and its chemistry, by no means exhaustive, has pointed out by some selective but typical examples that show uracils and their derivatives possess considerable synthetic potential. In most cases, a few easy reaction steps enable the synthesis of novel and highly interesting types of condensed heterocycles that are difficult to obtain by other synthetic means.

A new, general approach for the synthesis of heteroannulated 3,1-oxazin-4-ones

Abstract β-(N-Triphenylphosphoranyliden)-enamino esters afford the synthetically useful heteroannulated 3,1-oxazin-4-ones with aroyl chlorides in different solvents. The reaction proceeds in one step and in high yields and appears to be independent of the reactivity of the heterocyclic substrate.

Heterocondensed uracil betaines by three component reaction: iminophosphorane, heteroarene, isocyanate☆

Abstract 1,3-Dimethyl-6(triphenylphosphoranylideneamino)uracil 1 affords with pyridines and the isocyanates 2a-f in a novel type of a three component reaction pyrido[1,2-f]pyrimido-[4,5-d]pyrimidines 5a-h (X-ray analysis of 5a ).

Photochemistry of pesticides, 3: Photolysis of methyl 2-benzimidazolecarbamate (Carbendazim) in the presence of singlet oxygen

The photolysis of methyl 2-benzimidazolecarbamate (Carbendazim, 1) in methanol and in the presence of singlet oxygen, was studied. Dimethyl oxalate 4, 2-aminobenzimidazole 7, benzimidazole 9, N,N′-dicarbomethoxyguanidine 13, monocarbomethoxyguanidine 14, monocarbomethoxyurea 15, and 2-guanidinobenzimidazole 17, were isolated and identified in this reaction. A mechanism that accounts for the formation of the photoreaction products, is presented.

6-[(dimethylamino)methylene]amino-1,3-dimethyluracil: a versatile aza-diene substrate for cycloaddition and Michael-type reactions

Abstract 6-[(Dimethylamino)methylene]amino-1,3-dimethyluracil 1 undergoes formal [4+2] cycloaddition reactions with electron deficient olefins to give pyrido[2,3-d]pyrimidines. With DMAD or azodicarboxylates Michael addition occurs leading to pyrrolo[3,4-c]pyridines (X-ray analysis) and theophylline derivatives.

Heterocyclic β-Enamino Esters, Versatile Synthons in Heterocyclic Synthesis

Publisher Summary This chapter reviews heterocyclic β-enamino esters and an approach on annelation of a pyrimidine ring to an existing ring. While most classical enamines and open-chain enamino esters are obtained by condensation, for example, of a secondary amine with a keto compound, heterocyclic β-enamino esters can be obtained only by special reactions, such as rearrangement or direct syntheses. Heterocyclic β-enamino esters which are dihydrofurans, dihydro-4H-pyrans, and dihydro-4H-thiopyrans are easily accessible in a special case of acyl lactone rearrangement. While oxiranes afford with sodium ethylcyanoacetate only α-cyano-γ-butyrolactone—that is, the insertion of the hydroxyethyl moiety into ethyl cyanoacetate, thiiranes give with sodium cyanoacetate, in a one-step procedure, ethyl 2-amino-4,5-dihydrothiophene-3-carboxylate and some polymeric side products. Heterocyclic β-enamino esters differ in many aspects from enamines, open-chain β-enamino esters, and heterocyclic enamines, all of which point to a specific electron distribution in their enaminocarbonyl chromophore. Particular attention is paid to spectroscopic studies of these title compounds and to the consequences of their structures, protonation behavior, tautomerism, stability, and mesomeric forms.

An efficient iminophosphorane-mediated synthesis, NMR–IR spectroscopic and X-ray study of novel ferrocenylimidazole derivatives: Part 10. Study on ferrocenes

Abstract Starting from ethyl β-ferrocenyl-α-azidoacrylate ( 2 ), a series of novel 4-ferrocenylidene-1-aminoimidazolones ( 6a – j ) was prepared in a pathway involving an aza -Wittig reaction followed by condensation of the resulting carbodiimidoester with hydrazines. Formation of [1,2,4]triazines of type 7 was not observed. Simultaneously with the formation of 2 , an interesting transformation was also observed to afford a novel imidazolone derivative ( 3 ) containing two ferrocenyl groups. The structures of the products were determined by IR, 1 H- and 13 C-NMR spectroscopy (including 2D-COSY, DEPT, 2D-HMQC, and 2D-HMBC measurements), and in the case of compound 3 also by single-crystal X-ray analysis.

Heterocyclische β-enaminoester—III : NMR-spektroskopische untersuchungen zur protonierung heterocyclischer β-enaminoester

Zusammenfassung Partiell hydrierte heterocyclische β-Enaminoester vom Strukturtyp der 4,5-Dihydrofurane, -thiophene, der 5,6-Dihydro-4 H -pyrane und -thiopyrane erfahren in Trifluoressigsaure Protonierung in 3-Stellung (C β -Protonierung). Verlauf und Ort der Protonierung werden NMR-spektroskopisch untersucht und die Ergebnisse mit Protonierungsversuchen an ungesattigten, stickstoffhaltigen Verbindungen dieses Typs verglichen.

Photoreactions of 2-(4-thiazolyl)-1H-benzimidazole (thiabendazole) in the presence of singlet oxygen

Abstract The photooxidatior. of 2-(4-thiazolyl)-1H-benzimidazole (Thia=bendazole (1) in methanol in presence and absence of a photo=sensitizer (methylene blue), is investigated. Dimethyl oxalate, thiazole-4-(N-carbomethoxy)-carboxamide (6), methyl benzimida=zole-2-carboxylate (7), benzimidazole-2-carboxamide (8), and benzimidazole (9), were the main products of the photolysis. Some reaction mechanisms are discussed.

Chapter 3 - Wine and Heterocycles

Abstract In this review an original and unique approach was undertaken to unite the notions “heterocycles” and “wine principles.” Indeed, it is astonishing that natural wines contain numerous heterocyclic principles in varying quantities (as low as nanograms!) that contribute to flavor, smell, taste, and aftertaste (“finish”) sensations, all of which are characteristic of the different grape types. During aging and maturation of the wines in barrels and bottles, manifold additional heterocycles are formed or extracted. The odor threshold plays an important role in all cases, which is ultimately dependent on the chirality centers of the isomers involved in aroma. These heterocyclic classes are manifold: O-heterocycles (lactones, furans, flavones, carbohydrates), O-glucosides of terpenes, tannins, flavones, procyanidins, heterocyclic polyphenols with significant benefits to human health, S-heterocycles stemming from yeast metabolism and possessing strong organoleptic properties, N-heterocycles (pyrroles, pyrimidines, pyrazines, the latter constituents having a typical green pepper flavor and aroma). Finally, the role of fungicides and pesticides in wine is discussed.