Identification of alkyl-5H-6,7-dihydrocyclopenta[b]pyrazines in roasted meat flavor. Model reaction used as basis for natural product formation and new synthesis (author's transl)]

Identification of alkyl-5H-6,7-dihydrococyclopenta[b]pyrazines in roasted meat flavor. Model reaction used as basis for natural product formation and new synthesis. Seven alkyl-5H-6,7-dihydrocyclopenta[b]pyrazines have been identified in a roasted meat aroma obtained by thermolysis of the hydrosoluble flavor precursors of raw meat. Formation of these heterocyclics by condensation of hydroxycyclopentenones with aliphatic α-dicarbonyl compounds in the presence of ammonia has been confirmed by a model reaction. Alkyl-5H-cyclopenta[b]pyrazines and dicyclopenta [b,e]pyrazines are also obtained from this reaction, but have not yet been identified in roasted flavors. Preparation of the intermediates of the model reaction enabled development of an economical synthesis of 2,3,5-trimethyl-5H-6,7-dihydrocyclopenta[b]pyrazine.     

Aza-2-dienes-1,3. Partie 5. Préparation de N-aminoimidazoles, 3H-pyrroles,triazolo[1,2,4][1,5-a]pyrazines et imidazo[1,2-a]pyrazines

2-Aza-1,3-dienes. Access to N-Aminoimidazoles, 3H-Pyrroles, [1,2,4]Triazolo[1,5-a]pyrazines, or Imidazo[1,2-a]pyrazines Nucleophilic attack of 5-(dialkylamino)-2-aza-1,3-diene-1,1-dicarbonitriles (or their 1-methoxycarbonyl analogous) by hydrazines or hydrazdes gives substituted N-aminoimidazoles, [1,2,4]triazolo-[1,5-a]pyrazines, or α-dihydrazino derivatives. With α-amino esters (or analogous), imidazo[1,2-a]pyrazines are produced. Addtion of cyanide anions occurs also with formation of substituted 3H-pyrroles. Structures and rationalisation of this nucleophilic attack are discussed.     

Acylation of 3,4-Dihydropyrrolo[1,2-a]pyrazines

The direction of trifluoroacetylation with trifluoroacetic anhydride of 3,4-dihydropyrrolo[1,2-a]pyrazines containing an alkyl or aralkyl substituent in position 1 depends on both the structure of the 3,4-dihydropyrrolo[1,2-a]pyrazine starting materials and on the ratio of reagent:substrate. It may lead to both mono- and disubstituted products. Trifluoroacetylation of 1-methyl-3,4-dihydropyrrolo[1,2-a]pyrazines occurs at the methyl group. Acetylation of 3,4-dihydropyrrolo[1,2-a]pyrazines leads only to N-acetyl-substituted reaction products.     

Formylation of 3,4-Dihydropyrrolo[1,2-a]pyrazines

Formylation of 3,4-dihydropyrrolo[1,2-a]pyrazines containing alkyl or aryl substituents at position 1 has been studied under the conditions of the Vilsmeier reaction. The direction of the reaction depends on the structure of 3,4-dihydropyrrolo[1,2-a]pyrazine starting materials. Formylation of 1-methyl-substituted 3,4-dihydropyrrolo[1,2-a]pyrazines occurs at the methyl group.     

Synthesis of [1]benzothieno[2,3-e]pyrrolo[1,2a]pyrazines and related compounds

The synthesis of several [1]benzothieno[2,3-e]pyrrolo[1,2-a]pyrazines and other related heterocycles has been described. A study of the nmr spectra of these compounds was also reported.     

Dipyrrolo[1,2-a:2',1'-c]pyrazines. 8. Electrophilic Substitution in Dipyrrolo[1,2-a:2',1'-c]pyrazines and 5,6-Dihydrodipyrrolo[1,2-a:2',1'-c]pyrazines. Acylation of Dipyrrolo[1,2-a:2',1'-c]pyrazines

Esters, nitriles, and amides of dipyrrolo[1,2-a:2',1'-c]pyrazines have been synthesized by the acylation of dipyrrolo[1,2-a:2',1'-c]pyrazines and 5,6-dihydrodipyrrolo[1,2-a:2',1'-c]pyrazines with trichloroacetic acid chloride, p-tosyl isocyanate, and isocyanatophosphoric acid dichloride (Kirsanov isocyanate).     

Dipyrrolo[1,2-a;2':,1'-c]pyrazines. 7. Electrophilic Substitution of Dipyrrolo[1,2-a;2',1'-c]pyrazines and 5,6-Dihydrodipyrrolo[1,2-a;2',1'-c]pyrazines via Formylation of Dipyrrolo[1,2-a;2':,1'-c]pyrazines

A series of previously unreported aldehydes has been prepared by the formylation reaction of dipyrrolo[1,2-a;2':,1'-c]pyrazines and their 5,6-dihydro analogs by DMF and phosphorus oxychloride.     

Dipyrrolo[1,2-a;2',1'-c]pyrazines. 6. Electrophilic Substitution in a Series of Dipyrrolo[1,2-a;2',1'-c]pyrazine and 5,6-Dihydrodipyrrolo[1,2-a;2',1'-c]pyrazine Derivatives. Phosphorylation of Dipyrrolo[1,2-a;2',1'-c]pyrazines

We have studied the behavior of asymmetrically substituted dipyrrolo[1,2-a;2',1'-c]pyrazines and their 5,6-dihydro analogs under phosphorylation reaction conditions.     

Novel approach to the synthesis of perhydropyrazino[1,2-a]pyrazine derivatives from amino alcohols

2,4,7-Trisubstituted hydrogenated pyrazino[1,2-a]pyrazines as potential β-turn mimetics were prepared for the first time in a stereoselective synthesis from hexahydro[1,2,3]triazolo[1,5-a]pyrazines.     

The unusual formation of pyrrolo[1,2-a]pyrazines in the reaction of alkylpyrazine anions with trans-1,2-dichloroethylene

The reaction of alkylpyrazine anions with trans-1,2-dichloroethylene produces pyrrolo[1,2-a]pyrazines in low yields.     

One-Pot Three-Component Synthesis of 3-Aminoimidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridines and -pyrazines in the Presence of Silica Sulfuric Acid

Summary. The synthesis of 3-aminoimidazo[1,2-a]pyridines and 3-aminoimidazo[1,2-a]pyrazines through a condensation reaction of 2-aminopyridine or 2-aminopyrazine, aldehyde, and alkyl or aryl isocyanide in high yields at room temperature in the presence of silica sulfuric acid is described.     

Synthesis and some properties of N-unsubstituted pyrrolo[2,1-c]-1,3-diazacycloalkano[1,2-a]pyrazinones

Reactions of methyl 2-(2-formyl-1H-pyrrol-1-yl)alkanoates with unsubstituted aliphatic 1,2-, 1,3-, and 1,4-diamines gave N-unsubstituted pyrrolo[2,1-c]-1,3-diazacycloalkano[1,2-a]-pyrazinones. Some of them show ring-chain tautomerism. Transformations of these compounds led to a number of novel heterocyclic systems: 2,10-dihydro-3H,5H-imidazo[1,2-a]-pyrrolo[1,2-d]pyrazines, 2,3,4,11-tetrahydro-6H-pyrrolo[1??,2??:4,5]pyrazino[1,2-a]pyrimidines, 1,2,3,5,6,10b-hexahydroimidazo[1,2-a]pyrrolo[2,1-c]pyrazines, 1,3,4,6,7,11b-hexahydro-2H-pyrrolo[2??,1??:3,4]pyrazino[1,2-a]pyrimidines, and 2,3,4,5,6,7-hexahydro-1H-pyrrolo[2,1-c]-[1,4,7]triazacycloundecin-8(9H)-one.     

Diversity-oriented decoration of pyrrolo[1,2-a]pyrazines

Diversity-oriented synthesis of a chemical library based on a pyrrolo[1,2-a]pyrazine core is described by using palladium-catalyzed direct C6 arylation of pyrrolo[1,2-a]pyrazines with various aryl bromides. The starting materials, pyrrolo[1,2-a]pyrazines, were easily synthesized by the base-mediated N-alkylation of pyrrole-2-carboxaldehyde with several 2-bromoacetophenones followed by dehydrative cyclization with incorporation of nitrogen by the action of ammonium acetate. Introduction of other functional groups on this chemical scaffold is also discussed herein.     

Diversity-Oriented Synthesis of [2.2]Paracyclophane-derived Fused Imidazo[1,2-a]heterocycles by Groebke-Blackburn-Bienaymé Reaction: Accessing Cyclophanyl Imidazole Ligands Library

This report describes the synthesis of a [2.2]paracyclophane-derived annulated 3-amino-imidazole ligand library through a Groebke-Blackburn-Bienaymé three-component reaction (GBB-3CR) approach employing formyl-cyclophanes in combination with diverse aliphatic and aromatic isocyanides and heteroaromatic amidines. The GBB-3CR process gives access to skeletally-diverse cyclophanyl imidazole ligands, namely 3-amino-imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrazines. Additionally, a one-pot protocol for the GBB-3CR by an in situ generation of cyclophanyl isocyanide is demonstrated. The products were analyzed by detailed spectroscopic techniques, and the cyclophanyl imidazo[1,2-a]pyridine was confirmed unambiguously by single-crystal X-Ray crystallography. The cyclophanyl imidazole ligands can be readily transformed to showcase their useful utility in preparing N,C-palladacycles through regioselective ortho-palladation.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

Synthesis of diimidazo[1,2-a:2′,1′-c]pyrazines and diimidazo[1,2-a:2′,1′-c] [1,4]diazepines

Two new heterocyclic compounds, diimidazo[1,2-a:2′,1-c]pyrazine and 5H-diimidazo[1,2-a: 2,1′-c][1,4]diazepine have been synthesized by various routes from 2,2′-biimidazole (1) (2) together with some hydro, hydroxy and alkyl derivatives.     

Synthesis of polyarene derivatives of fused aziridines by Suzuki-Miyaura cross-coupling

A convenient and effective synthetic approach to potentially radiochromic polyarene derivatives of bi- and tricyclic aziridines utilizing modified Suzuki-Miyaura cross-coupling with catalysis in micellar media has been developed. A series of polyarene substituents were introduced into 1,5-diaryl-3,5a-dihydro-1H-azireno[1,2-c]imidazoles, 1,6-diaryl-1,3,4,6a-tetrahydroazireno[1,2-a]pyrazines, and 1,2-diaryl-1,1a-dihydroazireno[1,2-a]quinoxalines without degradation of the highly reactive aziridine ring system.     

Solvent Moisture-Controlled Self-Assembly of Fused Benzoimidazopyrrolopyrazines with Different Ring’s Interposition

This article shows that two extremely important families of fused heterocyclic assemblies, namely 6-methylbenzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazine and 5a-methyl-5a,6-dihydro-5H,12H-benzo[4,5]imidazo[1,2-a]pyrrolo[1,2-d]pyrazine, can be synthesized from only two available building blocks (N-allenylpyrrole-2-carbaldehyde and o-phenylenediamine) by controlling only one reaction parameter (water content of the medium). It should be emphasized that the latter class of compounds (with an a/d arrangement) is previously unknown. If the allene group is introduced not into the starting compound, but during the reaction (in superbase media), a heterocyclic ensemble, 5-methylbenzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazines, with a different position of the methyl group is formed.     

CNDO/2 calculations of some polyazaindenes

The theoretically estimated dipole moments of indolizine, imidazo[1,2-a]pyridine, imidazo-[1,5-a]pyridine and of pyrazolo[ 1,5-a]pyridine obtained by the CNDO/2 approximation have been compared with the experimental values. The bond angles and bond distances for these polyazaindenes have been estimated.     

A new, one-pot, multi-component synthesis of imines of 3-amino-2-arylimidazo[1,2-a]pyridines, 3-amino-2-arylimidazo[1,2-a]pyrazines, and 3-amino-2-arylimidazo[1,2-a]pyrimidines

An efficient, one-pot, multi-component synthesis of 3-amino-2-arylimidazo[1,2-a]pyridines, 3-amino-2-arylimidazo[1,2-a]pyrazines, and 3-amino-2-arylimidazo[1,2-a]pyrimidines is described. Heating a mixture of a 2-aminopyridine, 2-aminopyrazine or 2-aminopyrimidine, a benzaldehyde, and imidazoline-2,4,5-trione under solvent-free conditions afforded imine derivatives of the title compounds in excellent yields. Single-crystal X-ray analysis conclusively confirms the structure of these bridgehead bicyclic 5-6 heterocycles.