Photoisomerisierung von Pyrazolen und Indazolen zu Imidazolen bzw. Benzimidazolen und 2‐Amino‐benzonitrilen

Tiefenthaler, H.; Dörscheln, W.; Goth, Herbert; Schmid, Hans

doi:10.1002/hlca.19670500810

Cited by 76 publications

(15 citation statements)

References 12 publications

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“…Besides imidazoles themselves, other heterocyclic precursors can be used for the photochemical synthesis of heterocycles containing the imidazole nucleus. Photorearrangements of pyrazoles into imidazoles, which are generally obtained in low yields, have been reported; however, not all of these have been explained through the RCRE mechanism [2,3,5,37]. In fact, some experimental details have suggested that both the RCRE and ICI pathways are operative, and that open-chain intermediates are involved in some cases [5,38].…”

Section: Imidazolesmentioning

confidence: 99%

“…Moreover, in analogy to the pyrazole-to-imidazole photorearrangement, N-unsubstituted benzimidazoles are obtained, in yields that are generally low (11-36%), by the photoinduced rearrangement of the corresponding indazoles [3,37]. On the other hand, high yields of 1-alkyl-benzimidazoles (73-96%) are claimed from preparative-scale irradiations of 2-alkyl-indazoles through an ICI rearrangement [3,37].…”

Section: Imidazolesmentioning

confidence: 99%

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Synthesis of Heteroaromatics via Rearrangement Reactions

Vivona

Buscemi

Pibiri

et al. 2009

Handbook of Synthetic Photochemistry

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The varied family of heteroaromatics contains a large fraction of organic compounds, many of which have found important applications in different fields. Many synthetic methodologies have been developed to obtain target systems and, among them, photochemical methods represent valid and elegant alternatives when the final targets are difficult to obtain through ground-state chemistry. In this chapter, we describe the photochemical synthesis of heteroaromatic compounds through rearrangement reactions, particularly via ring-transformations of heterocyclic precursors [1][2][3][4][5][6][7].A classification of all photoinduced heterocyclic ring-transformation reactions is quite difficult to achieve due to the large variety of mechanistic pathways, experimental conditions and affecting parameters. In some cases, the photochemical product and the starting substrate have the same heterocyclic nucleus. In this chapter, we will refer to such reactions, characterized by the identity of the starting and final ring, as ring-degenerate rearrangements.In general, photoinduced rearrangements of heterocycles leading to heteroaromatic compounds may involve ring-contraction, internal cyclization, ring-expansion, ring-opening or ring-closure, and ring-fragmentation processes. As for five-membered rings, two processes will be repeatedly quoted throughout this chapter:. The ring contraction-ring expansion route (RCRE), which explains the formal interchange between two adjacent ring-atoms. This results from the photoinduced cleavage of the weakest bond in the ring with formation of a three-membered ring intermediate. The latter is then converted, either thermally or photochemically, into the final five-membered heterocyclic product (see e.g., Scheme 12.22). . The internal cyclization-isomerization route (ICI), which involves the formation of a bicyclic species featuring a single bond between the ring-atoms in the 2-and 5-positions of the original heterocycle. Sigmatropic shifts then occur, leading to different bicyclic intermediates from which the final products will arise (see e.g., Scheme 12.2).Handbook of Synthetic Photochemistry. Edited

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Section: Imidazolesmentioning

confidence: 99%

Section: Imidazolesmentioning

confidence: 99%

Synthesis of Heteroaromatics via Rearrangement Reactions

Vivona

Buscemi

Pibiri

et al. 2009

Handbook of Synthetic Photochemistry

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“…Few have much synthetic potential. [297,298] 12.4.2.1.2 Although 2-alkylindazoles are similarly transformed thermally into 1-alkylbenzimidazoles, the 1-alkylindazole isomers ring open to form 2-(alkylamino)benzonitriles.…”

Section: Synthesis By Ring Transformationmentioning

confidence: 99%

Product Class 4: Benzimidazoles

Neier¹,

Bellus²

2002

Category 2, Hetarenes and Related Ring Systems

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“…C 71,58 H 4,66 N 11,39% 1.4. 3,4-Bis(4-tolyl)sydnon (17). acetylchlorid wurde in Analogie zur Herstellung von a-Brom-a-phenylessigsaure-athylester [12] in a-Brom-u-(4-tolyl)essigsaure-athylester umgewandelt und dieser mit 4-Toluidin zum C, N-Bis(4-toly1)glycin-athylester umgesetzt.…”

Section: )) Diese Reaktionsweise Bietet F U R Alle Drei Nitriliumbetunclassified

“…Dreiring-Zwischenprodukte der Art 61 sind bei der Photoisomerisierung zahlreicher Sgliedriger Heterocyclen beobachtet worden (vgl. [17] und dort zit. Lit.).…”

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