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Zur Photochemie von 2, 1‐Benzisoxazolen (Anthranilen) und thermischen und photochemischen Umsetzungen von 2‐Azido‐acylbenzolen in stark saurer Lösung
Author(s) -
Doppler Thomas,
Schmid Hans,
Hansen HansJürgen
Publication year - 1979
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.19790620133
Subject(s) - chemistry , sulfuric acid , acetophenone , medicinal chemistry , nucleophile , ion , photochemistry , organic chemistry , catalysis
On the Photochemistry of 2, 1‐Benzisoxazoles (Anthraniles) and on the Thermal and Photochemical Decomposition of 2‐Azido‐acylbenzenes in Strongly Acidic Solution Anthranils 6 (Scheme 3) , when irradiated with a mercury high‐pressure lamp, in 96% sulfuric acid yielded, after work‐up, 2‐amino‐5‐hydroxy‐acylbenzenes 8 and as side products 2‐amino‐3‐hydroxy‐acylbenzenes 9 (cf. Schemes 5–7 and Table 1) . When C(5) of the anthranils 6 carries a methyl group a more complex reaction mixture is found after irradiation in 96% sulfuric acid (cf. Schemes 8 and 9) : 3, 5‐dimethyl‐anthranil ( 6d ) yielded (after irradiation and acetylation) 2‐acetyl‐ amino‐5‐methyl‐acetophenone ( 15 ), 2‐acetylamino‐5‐acetoxymethyl‐acetophenone ( 18d ) and 2‐acetylamino‐5‐acetoxy‐6‐methyl‐acetophenone ( 12c ). The latter product was also formed after irradiation of 3, 4‐dimethylanthranil ( 6c ) in 96% sulfuric acid. 3, 5, 7‐Trimethyl‐anthranil ( 6f ) formed under the same conditions 2‐acetylamino‐3, 5‐dimethyl‐acetophenone ( 15f ) and 2‐acetylamino‐5‐acetoxymethyl‐3‐methyl‐acetophenone ( 18f ). Since qualitatively the same product patterns were observed when the corresponding 2‐azido‐acetophenones 7 were decomposed in 96% sulfuric acid it is concluded that anthranilium ions (cf. 6b ‐H⊕, Scheme 11) on irradiation are transformed by cleavage of the N , O ‐bond into 2‐acyl‐phenylnitrenium ions (cf . 25b ‐H⊕) in the singlet ground state. The nitrenium ions are trapped directly by nucleophiles ( HSO ⊖ 4 in 96% sulfuric acid), thus, yielding the hydroxy‐acetophenones 8 and 9 (Scheme 11) . If C(5) is blocked by a methyl group a [1, 2]‐rearrangement of the methyl group may occur (cf. Scheme 13) or loss of sulfuric acid can lead to quinomethane iminium ions (cf . 32‐H⊕ , Scheme 13) which will react with HSO ⊖ 4 ions to yield, after hydrolysis and acetylation, the 5‐acetoxymethyl substituted acetophenones 18d and 18f . It is assumed that the reduction products (2‐acetylamino‐acetophenones 15 ) are formed from the corresponding nitrenium ions in the triplet ground state.