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Reaktionen von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit Phenolen und Halogenaromaten


Chandrasekhar, B Parthasarathi; Heimgartner, Heinz; Schmid, Hans (1977). Reaktionen von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit Phenolen und Halogenaromaten. Helvetica Chimica Acta, 60(227):2270-2287.

Abstract

The reactions of 3-dimethylamino-2,2-dimethylH-2-azirine (1) with phenols are described in chap. 1. The azirine 1 reacts with the 2-formyl- and 2-acetylphenols 5-8 to yield the N’-methylidene derivatives of 2-amino-N,N-dimethyl-isobutyramide 9-12 (Scheme 2, tautomeric form b). These products are in equilibrium with the tautomeric quinoide forms 9a-12a. Under similar conditions 4-hydroxybenzaldehyde did not react with 1. Reaction of 1 with 4-hydroxycoumarine (13) gives the 4-aminocoumarine 14 (Scheme 2). The mechanism of these reactions is analogous to the previously reported one for the reaction of 1 with cyclic enolisable 1,3-diketones [2][3]. Activated phenols with pKa-values <8, e.g. 2- and 4-nitrophenol, 2,4-dinitrophenol and pentachlorophenol, undergo addition reactions with 1 in boiling benzene solution to give the aniline derivatives 15-18 (Scheme 3). A reaction mechanism is given in Scheme 3: after protonation of the azirine 1 followed by attack of the phenolate ion at the amidinium-C-atom, the intermediate of type e undergoes a rearrangement to the spiro-Meisenheimer complexes of type f. Ring opening leads to 15-18. A similar reaction is observed for 2,4-dinitro-thiophenol and 1, giving 2-(N’-(2,4-dinitrophenyl)amino)-N,N-dimethyl-isobutyrothioamide (19). The azirine 1 reacts with the more acidic 2,4,6-trinitrophenol (picric acid) to yield 3,3,6,6-tetramethylpiperazine-2,5-bis(N,N-dimethyliminium) dipicrate (21, Scheme 4). The methacrylamidinium salt 22 is the only product (97% yield) in the reaction of 8-hydroxy-5,7-dinitroquinoline and 1 in acetonitrile solution. The reaction of 1 with picric acid can be explained in a similar way as the previously reported one with strong acids (cf. Scheme I , [1][3][5]). An alternative mechanism without formation of the 1-aza-allylcation c is postulated in Scheme 5, together with a mechanism which could explain the exclusive formation of 22 in the reaction of 1 with 8-hydroxy-5,7-dinitroquinoline. In chap. 2 a few reactions of the azirine 1 with aryl halides are reported. In the reaction with 2,4-dinitrofluorobenzene it is shown by UV. and NMR., that m,n and o are intermediates (Scheme 6). Working up the reaction mixture with water, hydrogen sulfide or benzylamine leads to the aniline derivatives 17, 19 and 26, respectively. With picryl chloride and 8-hydroxy-5,7-dinitroquinoline the azirine 1 undergoes a nucleophilic aromatic substitution to afford the intermediates p and q, which via deprotonation and ring opening give acrylamidine derivatives (27 and 29, Scheme 7 and 8). The steric hindrance in p and q between the aziridine ring and the two groups in o-position could be the reason for the different behaviour of the intermediates n and p or q (cf. Schemes 6 and 8).

Abstract

The reactions of 3-dimethylamino-2,2-dimethylH-2-azirine (1) with phenols are described in chap. 1. The azirine 1 reacts with the 2-formyl- and 2-acetylphenols 5-8 to yield the N’-methylidene derivatives of 2-amino-N,N-dimethyl-isobutyramide 9-12 (Scheme 2, tautomeric form b). These products are in equilibrium with the tautomeric quinoide forms 9a-12a. Under similar conditions 4-hydroxybenzaldehyde did not react with 1. Reaction of 1 with 4-hydroxycoumarine (13) gives the 4-aminocoumarine 14 (Scheme 2). The mechanism of these reactions is analogous to the previously reported one for the reaction of 1 with cyclic enolisable 1,3-diketones [2][3]. Activated phenols with pKa-values <8, e.g. 2- and 4-nitrophenol, 2,4-dinitrophenol and pentachlorophenol, undergo addition reactions with 1 in boiling benzene solution to give the aniline derivatives 15-18 (Scheme 3). A reaction mechanism is given in Scheme 3: after protonation of the azirine 1 followed by attack of the phenolate ion at the amidinium-C-atom, the intermediate of type e undergoes a rearrangement to the spiro-Meisenheimer complexes of type f. Ring opening leads to 15-18. A similar reaction is observed for 2,4-dinitro-thiophenol and 1, giving 2-(N’-(2,4-dinitrophenyl)amino)-N,N-dimethyl-isobutyrothioamide (19). The azirine 1 reacts with the more acidic 2,4,6-trinitrophenol (picric acid) to yield 3,3,6,6-tetramethylpiperazine-2,5-bis(N,N-dimethyliminium) dipicrate (21, Scheme 4). The methacrylamidinium salt 22 is the only product (97% yield) in the reaction of 8-hydroxy-5,7-dinitroquinoline and 1 in acetonitrile solution. The reaction of 1 with picric acid can be explained in a similar way as the previously reported one with strong acids (cf. Scheme I , [1][3][5]). An alternative mechanism without formation of the 1-aza-allylcation c is postulated in Scheme 5, together with a mechanism which could explain the exclusive formation of 22 in the reaction of 1 with 8-hydroxy-5,7-dinitroquinoline. In chap. 2 a few reactions of the azirine 1 with aryl halides are reported. In the reaction with 2,4-dinitrofluorobenzene it is shown by UV. and NMR., that m,n and o are intermediates (Scheme 6). Working up the reaction mixture with water, hydrogen sulfide or benzylamine leads to the aniline derivatives 17, 19 and 26, respectively. With picryl chloride and 8-hydroxy-5,7-dinitroquinoline the azirine 1 undergoes a nucleophilic aromatic substitution to afford the intermediates p and q, which via deprotonation and ring opening give acrylamidine derivatives (27 and 29, Scheme 7 and 8). The steric hindrance in p and q between the aziridine ring and the two groups in o-position could be the reason for the different behaviour of the intermediates n and p or q (cf. Schemes 6 and 8).

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Additional indexing

Other titles:Reactions of 3-dimethylamino-2,2-dimethyl-2H-azirine with phenols and aryl halides
Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:German
Date:1977
Deposited On:29 Oct 2014 12:52
Last Modified:05 Apr 2016 18:26
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:0018-019X
Funders:Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung
Publisher DOI:https://doi.org/10.1002/hlca.19770600718

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