Summary. Similarly to aldehydes [6j ketones form 3-oxazolines via cyclo-addition to the benzonitrile-methylides 2 that arise photochemically from the 3-phenyl-2H-azirines 1. With various ketones benzonitrile-isopropylide (2a) gives cyclo-addition products in very good preparative yields (scheme I ) . and benzonitrile-benzylide (2b) [8] react, however, sluggishly with ketones, smooth cyclo-addition being observed in their case only with Pactivateds ketones (2,2,2-trifluoro-acetophenonc, 1,1,1-trifluoro-2-propanone). With la acetonylacetonc forms the bis-adduct 12.While the azirine la reacts with cyclohexanone to yield essentially only the spiro-(3-oxazoline) 13, i t gives with cyclopentanone, depending on the reaction conditions, either the spiro-(3-oxazoline) 14 or the butenyl-3-oxazoline 15 (scheme 3). The formation of 15 has to be preceded by the photochemical formation of 4-pentenal from the ketone. Norcamphor and camphor react in a similar way (schemes 4 and 5 ) .The azirines la-c react smoothly with the kefo groups in acylcyanides and a-keto-esters, giving with the former 5-cyano-3-oxazolines and with the latter 5-ethoxycarbonyl-3-oxazolines (schemes 6 and 7 ) .p-Keto-esters (acetoacetic ester) form with the dipole arising from la the expected addition product 31 and, via the protonated dipole d (scheme 8), finally the benzylidene-acetoacetic ester.
Analogous results are obtained with malonodinitrile, trifluoro-acetamidc and other weak acids such as alcohols [29] [30] (scheme 9).The light-induced rearrangement of the bicyclic isoxazoline 37 into the oxazoline 38 is visualized as an intramolecular cyclo-addition reaction (scheme 70). The cyclo-addition in this case proceeds with the aldehyde group inversed as compared to the related intermolecular benzonitrileinethylide addition to aldehydes.Wie in fruheren Arbeiten gezeigt wurde, werden 3-Phenyl-2H-azirine vom Typ 1 durch Licht der Wellenlange ca. 300 nm in Benzonitril-methylide vom Typ 24) umgewandelt, die thermisch mit zahlreichen Dipolarophilen unter Cycloaddition zu funfl) 32. Mitteilungsiehe [l].
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4,Gegenwartige Adresse: Organisch-chemisches Institut der Universitat, A 1090 Wien. Neue hdresse : Institut dc chimie organique de l'Universit6, CH-1700 Fribourg, P6rolles. I n dieser Arbeit werden die Benzonitril-methylide(-isopropylide, -benzylide, usw.) in den Schemata stets in der dipolaren Form 2 geschrieben. Streng genommen ware, nach den IUPACNomenklaturregeln, die Bezeichnung ((Methylidea usw. nur auf die zu 2 mesomere Formel mit negativer Ladung auf dem Ylid-Kohlenstoffatom : anwendbar. HELVETICA CHIMICA ACTA -1. 01, 57, Fasc. 7 (1974) -Kr. 236 gliedrigen Heterocyclen abreagieren [Z-81. Im folgenden berichten wir iiber die Reaktionen der Phenylazirine mit Ketonen, Acylcyaniden und Ketoestern. Ketonen. -((Aktivierte)) Ketone wie Z,Z,Z-Trifluor-acetophenon und 1, 1, 1-Trifluor-Z-propanon addieren sich glatt an die aus den 3-Phenyl-2H-azirinen l a und l b photochemisch in Benzollosung mit einer Quecksilber-Hochdrucklampe hinter Pyrex erzeugte...
