Tieftemperaturbestrahlungen von 3‐Phenyl‐2H‐azirinen

Abstract

2,2,3-Triphenyl-ZH-azirine (4a) in a matrix of 2,2-dimethylbutane/pentane 8 : 3(DMBP) at -185' gave rise on irradiation with light of 250-350 nm to a new UV.-maximum at 350 nm (Fig. 1). We assign the dipole benzonitrildiphenylmethylide (la) to this new maximum. Irradiation with monochromatic light of 366 nm destroyed this maximum and the initial absorption curve reappeared (Fig. 2). When the azirine 4a was photolysed in DMBP at -185" in the presence of methyl trifluoracetate (TFEM), the maximum at 350 nm was obtained again. This maximum vanished upon increasing the temperature to -160". Through gas chromatography we were able to show that 5-methoxy-5-trifluormethyl-2,2,4-triphenyl-3-oxazoline (6a) was produced. 6a was also obtained upon irradiation of 4a a t room temperature in the presence of TFEM (scheme 1 and table 1). Modification of the previously described experiment, in which the maximum a t 350 nm was extinguished in the matrix due to irradiation at 366 nm gave, after warm up, almost no dipole adduct 6a (table 1). From these experiments, an extinction coefficient of 17,000 for the 350 nm maximum of la, was calculated. These experiments have shown that irradiation of triphenylazirine 4a leads to the dipole la, which can be reversed photochemicallybut not thermallyinto azirine 4a. l a reacts a t less than -160" with TFEM to give adduct 6a. The results which were obtained with triphenylazirine 4a could be correspondingly obtained with 2,J-diphenyl-2H-azirine 4b (Fig. 3, scheme 2 and table 2 ) . The dipole l b showed two UV.maxima at 330 nm (e = 17,500) and 343 nm (E = 21,000). Later experiments established. that the two maxima belonged to a single dipole species.The dipole lc obtained upon irradiation of 2,2-dirnethyl-3-phenyl-ZH-azirine (4c) in DMBP at -190°, appears to absorb in the same region as the azirinc 4c. The presence of the dipole lc was univocally established by low temperature trapping experiments with TFEM. The dipole l a showed no ESR.-spectrum characteristic for a triplet state. We assume therefore, that la is in a singlet state. Photolysis of oxazolinone 7 at -190" in DMBP led to the dipole l a with loss of CO,. la recombines apparently in considerable amount with the CO, trapped in the matrix to l ) %) 27. Mitt. iiber Photoreaktionen; 26. Mitt. [l] ; 25. Mitt. [Z].

Photoinduzierte Reaktionen von 3‐Phenyl‐2H‐azirinen mit Carbonsäureestern 40. Mitteilung über Photoreaktionen

“…Bereich 3,4 ppm, wenn an C(2) in cis-Anordnung ein H-Atom oder eine CH3-Gruppe steht (vgl. NMR.-Spektren von 2, 13, trans-und cis-15).…”

Photoinduzierte Cycloadditionen von aliphatischen 2H‐Azirinen. 37. Mitteilung über Photoreaktionen

“…siehe [l] und Azodicarbonsaureestern in guten Ausbeuten unter Bildung von 5-gliedrigen Heterocyclen zu reagieren (vgl. [2][3][4][5][6][7][8] und dort zitierte Literatur).…”

Photochemische Cycloadditionen von 3‐phenyl‐2h‐azirinen mit Aldehyden. 31. Mitteilung über Photoreaktionen

“…-160" ablaufende Reaktion darstellt [3]. Man kann annehmen, dass dies auch fiir die Reaktion mit Aldehyden und vergleichbaren Dipolarophilen gilt l o ) .…”

“…Hierbei erfolgt als erster Reaktionsschritt die photochemische Ringoffnung der 3-Phenyl-2H-azirine 1 zu Benzonitril-methyliden 2 (Schema 1). Dt:r Dipol 2e (R1 = R2 = 1%) liess sich kurzlich bei der Bestrahlung von 1 e (R1 = R2 = Ph) in einer Matrix bei -185" durch sein UV.-Spektrum direkt nachweisen [3] ; er reagierte sclion bei ca. - Ketonen, Estcrn und Nitrilen [6--8], sowie mit kuniulierten Doppelbindungen [a] 1111).…”