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Notes: Kondensation von p-Dimethylamino-benzaldehyd mit Acetophenon führt zu einem Diketon, das in einen neuartigen Farbstoff übergeführt wurde, der gleichzeitig Chinon- und Pyryliumderivat ist.

Notes: Am Beispiel der Pyrrolsulfonsäuren läßt sich der Mechanismus der Pyrrol-Austauschreaktionen beweisen. Elektrophile Reagenzien addieren sich an das den austauschfähigen Substituenten tragende C-Atom des Pyrrolkerns zu Pyrrolen-Zwischenverbindungen, die den Substituenten abstoßen.

Notes: Durch Bromierung der Pyrrol-α-sulfonsäure I wurden, unter Oxydation des Pyrrolkerns, Derivate des Pyrrolens und des Pyrrolenons erhalten. Aufgrund dieser neuartigen Reaktion konnten von H. Fischer und Mitarbeitern10) beschriebene Verbindungen als Pyrrolenderivate erkannt werden. Bei der Bromierung einkerniger Pyrrolderivate wurde die Bildung eines dreikernigen blauen Farbstoffs neben Dipyrrylmethenen aufgefunden.

Notes: Irradiation of 4-Allylated 2,6-Dimethylanilines in Methanol4-Allyl-, 4-(1′-methylallyl)-, 4-(2′-butenyl)-, and 4-(1′,1′-dimethylallyl)-2,6-dimethylaniline (14-17; cf. Scheme 3) were obtained by the acid catalysed, thermal rearrangement of the corresponding N-allylated anilines in good yields. Aniline 14, when irradiated with a high pressure mercury lamp through quartz in methanol, yielded as main product 4-(2′-methoxypropyl)-2,6-dimethylaniline (22; cf. Scheme 4) and, in addition, 2,6-dimethyl-4-propylaniline (18) and 4-cyclopropyl-2,6-dimethylaniline (23). The analogous products, namely erythro- and threo-4-(2′-methoxy-1′-methylpropyl)-2,6-dimethylaniline (erythro- and threo-24), 2,6-dimethyl-4-(1′-methylpropyl)aniline (19), trans- and cis-2,6-dimethyl-4-(2′-methylcyclopropyl)aniline (trans- and cis-25), as well as small amounts of 4-ethyl-2,6-dimethylaniline (26), were formed by irradiation of 15 in methanol (cf. Scheme 5). When this photoreaction was carried out in O-deuteriomethanol, erythro- and threo-24 showed an up-take of one deuterium atom in the side chain. The mass spectra of erythro- and threo-24 revealed that in 50% of the molecules the deuterium was located at the methyl group at C(1′) and in the other 50% at the methyl group at C(2′) (cf. Scheme 6). This is a good indication that the methanol addition products arise from methanolysis of intermediate spiro[2.5]octa-4,7-dien-6-imines (cf. Scheme 7). This assumption is further supported by the photoreaction of 17 in methanol (cf. Scheme 8) which led to the formation of 4-(2′-methoxy-1′,2′-dimethylpropyl)-2,6-dimethylaniline (28) as main product. The occurrence of a rearranged side chain in 28 can again be explained by the intervention of a spirodienimine 31 (cf. Scheme 9). In comparison with 14, 15 and 17, the 2′-butenylaniline 16 reacted only sluggishly on irradiation in methanol (cf. Scheme 10). It is suggested that all photoproducts - except for the cyclopropyl derivatives which are formed presumably via a triplet di-π-methane rearrangement - arise from an intramolecular singlet electron-donor-acceptor complex between the aniline and ethylene chromophor of the side chain. Protonation of this complex at C(3′) or C(2′) will lead to diradicals (e.g. 33 and 34, respectively, in Scheme 11). The diradicals of type 33 undergo ring closure to the corresponding spirodienimine intermediates (e.g. 31) whereas the diradicals of type 34 take up two hydrogen atoms to yield the photo-hydrogenated compounds (e.g. 21) or undergo to a minor extent fragmentation to side chain degraded products (e.g. 30; see also footnote 7).-Irradiation of 4-ally-2,6-dimethylaniline (14) in benzene or cyclohexane yielded the corresponding azo compound 38 (cf. Scheme 12), whereas its N,N-dimethyl derivative 41 was transformed into the cyclopropyl derivative 42. The allyl moiety in 14 is not necessary for the formation of azo compounds since 2,4,6-trimethylaniline (39) exhibited the same type of photoreaction in benzene solution.

Notes: Acid-Catalysed Formation of Imidazoles from 2H-Azirines or Vinylazides and NitrilesThe reaction of 2H-azirines with nitriles in the presence of boron trifluoride etherate to yield the corresponding imidazoles is described. 2,3-Diphenyl-2H-azirine (10) gives 2-substituted 4,5-diphenyl imidazoles in moderate bis good yields (see Table 1). The reaction of 10 with acrylonitrile only leads to the formation of 4,5-diphenyl-2-vinylimidazole (17). No products resulting from an addition to the C,C double bond are observed. 2H-Azirine 10 and ethyl cyanoacetate yield the expected imidazole 18 (30%) but also 2-cyanomethyl-4,5-diphenyloxazole (20; 7%) (see Scheme 4). The yield of imidazole formation mainly depends on the substituents in position 2 of the 2H-azirines (see Scheme 6), a change of the substitutents in position 3 having only little influence. The best yields are observed with a phenyl group at C(2) of the 2H-azirines. These observations are in agreement with the occurrence of 1-azaallyl cations formed by ring opening of the 2H-azirines linked to the Lewis acid (boron trifluoride). Similar results are obtained with the corresponding vinyl azides with the exception of 1-azido-1-phenylethylene (28). Whereas the corresponding 3-phenyl-2H-azirine (24) gives 2,4-diphenylimidazole (33; Scheme 6) in the presence of benzonitrile and boron trifluoride etherate, the azide 28 yields only acetanilide (86%). In the presence of triethyloxonium tetrafluoroborate 2H-azirines and benzonitrile react to yield the corresponding 1-ethylimidazoles (see Scheme 9). This again demonstrates that 1-azaallyl cations must be intermediates which react with the nitrile presumably in a Ritter type reaction. 13C-NMR. spectra of 2H-azirines are also reported (Table 2).