Zum Mechanismus der Photochemie von 2‐Alkylindazolen in wässerigen Lösungen

Heinzelmann, Willy; Märky, Michael; Gilgen, Paul

doi:10.1002/hlca.19760590709

Cited by 15 publications

(6 citation statements)

References 14 publications

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“…Bei fallenden pH-Werten entstehen in zunehmendem Masse 7-Acyl-1,3dihydro-2H-azepin-2-one, deren Bildung erst wieder bei pH-Werten < 3.5 zugunsten von 3-Acyl-1,3dihydro-2H-azepin-Zonen abnimmt [6] IS]. Bei pH-Werten < 1 wird schliesslich auch die Bildung dieser Verbindungen unterdruckt \6] [8], und es entstehen nur noch 2-Amino-5-hydroxy-acylbenzole, also die von uns erstmals beobachteten Verbindungen vom Typ 3 (Schema 1). Alle in Abhangigkeit vom pH-Wert beobachteten Photoreaktionen der 2-Alkylindazole stellen Singulett-Reaktionen dar [8].…”

Section: Schema Iunclassified

“…Bei pH-Werten < 1 wird schliesslich auch die Bildung dieser Verbindungen unterdruckt \6] [8], und es entstehen nur noch 2-Amino-5-hydroxy-acylbenzole, also die von uns erstmals beobachteten Verbindungen vom Typ 3 (Schema 1). Alle in Abhangigkeit vom pH-Wert beobachteten Photoreaktionen der 2-Alkylindazole stellen Singulett-Reaktionen dar [8]. In Glasern (95proz.…”

Section: Schema Iunclassified

“…Bei sehr empfindlichen Photolyseprodukten wurde das nach dem Filtrieren uber die Kieselgelsaule erhaltene Reaktionsgemisch sofort mit Essigsaureanhydrid/Pndin bei RT. (5)(6)(7)(8)(9)(10) Std.) acetyliert.…”

Section: ) Bambergerunclassified

“…Das Fluoreszenspektrum von 2,3-Dimethylindazol in neutraler und protonierter Form ist in [8] wiedergegeben. Schon von Auwers & Diiesberg [18] fanden, dass 10 und 1 bei der Umsetzung mit Methyljodid dasselbe 1,2-Dimethylindazolium-jodid ergeben.…”

unclassified

“…exper. Teil und auch[8]). 12) Hierbei spielt sicher der Bindungsenergieunterschied zwischen der ((starken,) C,X-und der ((schwachenr N,X-Bindung (X= OR, CI) sowie die starke Ladungsdelokalisierung eine entscheidende Rolle.…”

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Zur Photochemie von 1H‐ und 2H‐Indazolen in saurer Lösung

Georgarakis

Schmid

Hansen

1979

Helvetica Chimica Acta

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It is shown that I Hand 2H-indazoles (cf: Scheme2) on protonation ( 0 , l~ H2S04 in water or alcoholic solution) give analogous indazolium ions (see Fig. 1 and 2) which on irradiation undergo heterolytic cleavage of the N(l), N(2) bond whereby aromatic nitrenium ions in the singlet ground state are formed (cf: Scheme 13). If the para position of these nitrenium ions is not occupied by a substituent (e.g. a methyl group) they are readily trapped by nucleophiles present (e.g. water, alcohols, chloride ions) to yield the corresponding 5-substituted 2-amino-benzaldehydes or acetophenones (cf: Schemes 4-10). Photolysis of indazole (4) and 3-methyl-indazole (5) in 0,75 N H$O, in alcoholic solutions gives in addition minor amounts of the corresponding 3-substituted 2-amino-benzaldehydes and acetophenones, respectively (cf: Schemes 6 and 8 and Table 2). Phenylnitrenium ions carrying a methyl group in the para position give in aqueous sulfuric acid mainly the reduction products, i.e. 2-amino-5-methyl-benzaldehydes (cf: Schemes I 1 and 12 and Table 3). In methanolic sulfuric acid, in addition to the reduction products, 6-methoxy substituted benzaldehydes are found (cf: Schemes I 1 and 12 and Table 3) which are presumably formed by an addition-elimination mechanism (cf: Scheme 18). It is assumed that precursors of the reduction products are the corresponding nitrenium ions in the triplet ground state. Singlet-triplet conversion of the nitrenium ions may become efficient when addition of nucleophiles to the singlet nitrenium ions is reversible (cf: Scheme 22) thus, enhancing the probability of conversion or when conjugation in the singlet nitrenium ions is disturbed by steric effects (cJ Scheme 20) thus, destabilizing the singlet state relative to the triplet state.

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Section: Schema Iunclassified

Section: ) Bambergerunclassified

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Zur Photochemie von 1H‐ und 2H‐Indazolen in saurer Lösung

Georgarakis

Schmid

Hansen

1979

Helvetica Chimica Acta

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Entwicklungen in der Arylnitren‐Chemie: Synthesen und Mechanismen

et al. 1979

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Developments in Arylnitrene Chemistry: Syntheses and Mechanisms [New synthetic methods (31)]

Iddon¹,

Meth‐Cohn²,

Scriven³

et al. 1979

Angew. Chem. Int. Ed. Engl.

151

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Aryl-and heteroaryl-nitrenes can take part in intra-and intermolecular reactions in both of their possible electronic states (triplet and singlet). In this review we have endeavored to highlight recent synthetic uses of these reactive intermediates as well as draw attention to avenues open to further exploration in this field. Singlet arylnitrenes will interact with suitable orthopositioned substituents to give a variety of fused azoles, some in excellent yield. In suitable solvents and in presence of amines and alcohols, phenylnitrenes undergo ring expansion to azepines which can also occur in nitrenes of certain fused bicyclic aromatics (naphthalene, quinoline, isoquinoline, benzo[b]thiophene). The latter nitrenes may also give rise to o-diamines which are useful starters for further heterocyclic synthesis. Triplet arylnitrenes (usually regarded as having only a nuisance effect in synthetic work) may also be utilized in practicable heterocyclic syntheses within a suitable molecular framework. Decomposition of aryl azides in a mixture of an organic and polyphosphoric acid leads to fused oxazoles. The mechanism is discussed for all the reactions considered.

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Zum Mechanismus der Photochemie von 2‐Alkylindazolen in wässerigen Lösungen

Cited by 15 publications

References 14 publications

Zur Photochemie von 1H‐ und 2H‐Indazolen in saurer Lösung

Zur Photochemie von 1H‐ und 2H‐Indazolen in saurer Lösung

Entwicklungen in der Arylnitren‐Chemie: Synthesen und Mechanismen

Developments in Arylnitrene Chemistry: Syntheses and Mechanisms [New synthetic methods (31)]

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