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Tieftemperatur‐Photochemie von 2‐Alkyl‐indazolen
Author(s) -
Heinzelmann Willy
Publication year - 1978
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19780610208
Subject(s) - chemistry , protonation , alkyl , photochemistry , tautomer , singlet state , hydrogen atom abstraction , indazole , excited state , decarboxylation , triplet state , intersystem crossing , reactivity (psychology) , singlet fission , ion , medicinal chemistry , hydrogen , organic chemistry , molecule , catalysis , pathology , nuclear physics , medicine , physics , alternative medicine
Photochemistry of 2‐Alkyl‐indazoles at Low Temperatures 2‐Alkyl‐indazoles 1 undergo a variety of photoreactions (Scheme 1) which have been shown to proceed via excited singlet states of the neutral and protonated indazole, respectively [6]. The quantum yields of these reactions decrease with decreasing temperature; around 150°K the 2‐alkyl‐indazoles are practically reactivity of both neutral and protonated indazoles is observed (Fig. 3), yielding 2‐amino‐acylbenzenes 7 , obviously formed by hydrolysis of the corresponding imines 6 (Scheme 2). Yellow ‘intermediates’ (Figs. 1 and 2) which are observable only at low temperatures upon irradiation of neutral indazoles but are rather stable even at room temperature in acid solutions, could be identified as quinoid tautomers 8 of the imines (Scheme 4). It is assumed that the formation of the imines 6 proceeds via an arylnitrene or arylnitrenium‐ion 13 (Scheme 5) and subsequent hydrogen abstraction, the nitrenes being formed directly in their triplet ground‐state from the triplet state of the indazoles.