Whereas 2H-benztriazoles are photochemically stable, 1 H-benztriazoles yield biradicals after splitting ofT nitrogen. These biradicals attack aromatic substratessuch as anisole, toluene, fluorobenzene or benzonitrile preferentially in the o-and p-positions with formation of the corresponding o-amino biphenyls (cf. schemes 2-5). With a deficiency of aromatic substrate, attack at the o-

the case of 1,3-diaryl-lH-diazirines which are intermediates in the photolysis of 3,4diarylsydnones [loj.Photolysis of 4 yielded 4-phenyl-3-phenyliniino-l-azabicyclo[2,1,0]pentane 1101, whereas 2,4,5-triphenyl-imidazole Summary. Irradiation of 3-phenyl-2H-azirine (2) in benzene solution with a high-pressure inercury lamp yields 4,5-diphenyl-l, 3-diazabicyclo[3,1,0]hex-3-ene (4) and not 3-phenylimino-4phenyl-l-azabicyclo[2,l,0]pentane (11, as had been reported previously by others [ 2 ] . 2-Methyl-3phenyl-2 H-azirine (3) yields on irradiation a 2 :1 mixture of 2-exo, 6-exo-and 2-endo, 6-exo-dimethyl-4,S-diphcnyl-l, 3-diazabicyclo[3,1,0]hex-3-ene (2-exo, 6-exo-and 2-endo, 6-exo-5). Irradiation of 2,3-diphenyl-2 H-azirine (8) leads t o thc formation of 2,4,5-triphenyl-imidazole (9) and tetraphenylpyrazine (10). The suggested reaction path for the generation of 9 and 10 is shown in Scheme 2 .Kurzlich wurde mitgeteilt [ 21, dass bei der Bestrahlung von a-Azidostyrol in benzolischer Losung init einer Quecksilber-Hochdrucklampe neben 3-Phenyl-2H-azirin (2) (vgl. auch 131) in 10% Ausbeute ein weiteres, kristallines Photoprodukt (Snip. 137-140') isoliert werden konnte, dem auf Grund seiner spektralen Daten (NMR .-, 1) 2) 18. Mitteilung uber Photoreaktionen; 17. Mitteilung: siehe [l]. Eine ausfuhrliche Mitteilung sol1 in dieser Zeitschrift erscheinen

2 3 I11 72)Sunzmary. Irradiation of 2-methyl-(1 c ) and 2,2-ciimctliyl-3-pheny1-2H-azirine (1 d) in benzene solution in the prcscnce of carbon dioxidc yields 2-methyl-4-phenyl-(3 c ) and 2,2-dimethpl-4-phen~l-3-oxazolin-5-one (3 d), respcctively. Similar cycloadducts are observed (see table) when 2,3-diphenyl-ZH-azirinc (1 b) and 1 d are irradiated in the prcscnce of phcnylisocyanate, o-tolylisocyanate, phenylisothiocyanatc or cli-o-tolyl-carbotliiini~le, 3-Phenyl-2H-aairine 1 werden photocliemisch unter Losung der Cj2)-C(3)-Bindung in Benzonitri 1-methylenylide 2 uberfulirt (21 131 141. Eine besonders einheitliche Reaktiori beobachtete man bei der Bestrahlung (Pyrex-Filter) von 3-Phenyl-2H-1 2 20. Mitteilung iiher Photoreaktionen; 19. Mitteilung: [l].Eine ausfiihrliclie Mitteilung sol1 spater in dieser Zeitschriit crscheinen. 2,

Photochemical Synthesis of 4-Phenyl-3-oxazolin-5-ones and their Thermal Dimerization. -Summary. Irradiation of 3-phenyl-2H-azirines affords reactive benzonitrilemethylide intermediates, which can be trapped by carbon dioxide to yield 4-phenyl-3-oxazolin-5-ones (Scheme I ) . The first section of the paper deals with the experimental description of this reaction, which already has been preliminarily communicated. Upon irradiation the 3-oxazolin-5-ones undergo photoextrusion of carbon dioxide to reform the corresponding benzonitrile-methylidcs, which can be trapped by dimcthyl acetylenedicarboxylate.In the second section of the paper, reactions of Z-mcthyl-4-phenyl-3-oxazolin-5-one (3c) are described. Upon heating to 130", this compound is partially converted to 2-mcthyl-4-phenyl-Zoxazolin-5-one (azlactone 4e). Prolonged heating of 3c affords the dimcr 7 (Scheme 3) as well as the imidazole derivative 9 (Scheme4). Compound 7 is related to the 'Riigheimer compound' C18H14N204, formed from hippuric acid methylester. The structure of 7 was determined by X-ray crystallography and this supports the formula assigned earlier to the 'Kiigheinzer compound' (12) and related pyrrolidin-2,4-diones. The possible mechanism of the thermal formation of 7, which is also base catalysed, is represented in Scheme 3, the one for the formation of the imidazol 9 in

748 Photochemische Cycloadditionen von 3-Phenyl-2H-azirinen mitBenzoyl-, khoxycarbonylund Vinylphosphonaten 34. Mittcilung iibcr Photorcaktionenl) von Nikolas Gakis3), Heinc Heimgartner itnd Hans Schmid Clrganisch-cheraischcs lnstitut der 1lnivi:rsitiit Zilrich, Xaniistrassc 76, 8001 Zurich (21. 11. 74) Summary. The irradiation of thc 3-phcnyl-2 H-axirincs la-c in thc prcscnce of dicthyl bcnzoylphosphonatc (8) in cyclohcxanc solution, using a nitrcury high prcssurc lamp (pyrax filter), yields the diethyl (4,5-~liphi:nyl-3-oxszr~1iti-5-yl)-phosp~~onat~s 9a.. c (Scheme 3). In tho Caso of Ib a mixture of two tlissturi:orncric 3-oxazolines, resulting from a regiospecific hit non-stercospccific cycloadditiori of thc Lenzonitrilu-hcnzylide dipolc 2b to the carbonyl group of the phosphonatc 8, was isolatcd.Benzonitrile-isopropyIide (2a). gencratecl Irom 2,2-dirnc:thyl-3-plicnyl-Z~-~zirine (la), undergoes B cycloaddition rcaction to the cster-cnrbonyl group of dicthyl cthoxycarbnylphosphonattc (15) with the Sitme rcgiospxificity to givt: the 3-oxazoline clcrivative 16 (Scheme 5).'hc azirines la-c, on irradiation in b-nxcne in 0 1 1 : presence of diethyl ~Inylphosphonate (17) give non-rtKiosI,ccifically the dl-pyrrolinus 13a-c and 14a-c (Scheme 6 ) . Photochemisch aus 3-l'henyl-2 H-azirinen des Typs 1 crzeugte Benzonitrilmethylid-Diyolc 2 rcagicrcn mit Aaktivicrten N C , Cund C , X-(X = N, 0, S) -Doppeloder -DreiEachbindun&-n im allgemeinen rcgiospezifisch zu fiinfgliedrigen Hetcrocycleri des Typs 3 (Schema 7) ([Z-51 utid dort zitierte Iiteratur). In diesem Zusammenhang stcll te sich dic Frage, ob Dipole dcs Typs 2 auch mit P. 0-Doppelbindungen 1, 3-dipolarc Cycloadditioncn eingehen. Schema 1 3 (X = CR,, NR, 0) Nach 2-3stdg. Bestralilung eincr 1,75 x 1 0 -2~ benmlischen Losung von 2,2-Dimethyl-3-phenyl-2H-azirin (1 a) rnit ciner Quecksilber-Hochdtucklampe hinter Pyrex in Gegenwxt voii ca. 2 Mol-Aquiv. Diathyl-[benzyl-] oder Dimethyl-[methylphosphonat] (4 bzw. 5) konnten keine Phos~l~onat-Addukte nachgewiesen werden. 1) 33. Mitt. siehe [ll. Infolge von Zuriickstellung dcr Veriiffentlichung dcr 33. und 34. Mitt. sind inzwischcn einige wciterc: Mittcilungen dieser Reihc crschiencn, siehc [l his]. *) Teil der gcplsnten Iksertntion N. Gakis, Univcrsitat Zurich. --~ 2,62 x lo-*,) mit einer Quecksilber-Hochdrucklampe hinter Pyrex tropfcnweise Benzoylphosphonat 8 zugegeben (vgl. exper. 'Tcil), so isoliertc man DiiitliyI-['(2,2dimethyl-4,5-diphenyl-3-oxazolin-5-yl)-phosp~ionat~ (9 a) in 42% Ausbeute4) (Schema 3). UV.-, 1R.-, 1H-NMK.und Massenspektrcn (Tab. 1 und cxper. Tcil) stehen tnit der vorgeschlagenen Strulctur 9a in Einklarig (vgl. l-i] [4]).~ 3)7 zersetzte sich h i dcr chramatographischcn Reinigurig zu 5-Acetyl-5-hydroxy-2. Z-dimcthyl-4-phenyl-3-oxaznlin. Ausbeuteangabcn hzogen auf cingesetztes Azirin und isoliertcs Produkt. Tabellc Spektvale Daten dev hergestellles D i a t h y E -~( 4 -p h e l l ; v I -3 -o~a~o Z~~-5 -y l ) a~e ] VerbindungCV. (EtOH) IR. (Film) 'H-NMR. (100 MHz) 8 ) lSC-KMR.b) aromat.