Synthesis of 4H-pyrazolo- and 4H-pyrrolophenothiazin-4-one derivatives

5-Methyl- and 6-methyl-2-phenyl-2H-indazole-4,7-diones were condensed with 2-aminobenzenethiol or 6-substituted-3-aminopyridine-2(1H)thiones 4 to produce a new type of 5-methyl-2-phenyl-4H-pyrazolophenothiazin-4-ones or 8-substituted-7-aza-5-methyl-2-phenyl-4H-pyrazolophenothiazin-4-one derivatives. From 6-bromo-2,5-dimethyl-1,3-diphenyl-2H-isoindole-4,7-dione and 4 8-substituted-7-aza-2,5-dimethyl-1,3-diphenyl-4H-pyrrolophenothiazin-4-one derivatives were also prepared.     

Photoinduced Molecular Transformations. Part 142. One-step syntheses of 1H-benz[f]indole-4,9-diones and 1H-indole-4,7-diones by a new regioselective photoaddition of 2-amino-1,4-naphthoquinones and 2-amino-1,4-benzoquinones with alkenes

The 2,3-dihydro-1H-benz[f]indole-4,9-diones 3a–d , h were formed in a one-step reaction in 13–82% yield by an unprecedented [3 + 2] regioselective photoaddition of 2-amino-1,4-naphthoquinone ( 1 ) with various electronrich alkenes 2 (Scheme 1, Table). The [3 + 2] photoadducts derived from 1 with vinyl ethers and vinyl acetate gave 1H-benz[f]indole-4,9-diones 4e , f , i , in 33–72% yield, by spontaneous loss of the corresponding alcohol or AcOH from the resulting adducts; 4i has a kinamycin skeleton. The [3 + 2] photoaddition also took place on irradiation of the differently substituted amino-1,4-benzoquinones 6 , 7 , and 12 and excess alkenes 2 in benzene, giving 1H-indole-4,7-dione derivatives 13 and 14 (Scheme 3), 15a and 16 (Scheme 4), and 18 (Scheme 4), respectively. The initial products in these photoadditions were proved to be hydroquinones, the air oxidation of which yielded the heterocyclic quinones; 2,3-dihydro-2-methoxy-2-methyl-5-phenyl-1H-indole-1,4,7-triyl triacetate ( 19 ) was isolated after treatment of the crude photoaddition mixture obtained from 2-amino-5-phenyl-1,4-benzoquinone ( 7 ) and 2-methoxyprop-1-ene ( 2f ) with Ac₂O and pyridine under N₂. A pathway leading to the annelated hydroquinones involving ionic intermediates arising from an electron transfer in these photoadditions is proposed (Scheme 5).     

Synthese und polarographisches Verhalten von 2H-Isoindol-4,7-dionen

Summary 2-Phenylthio-1,4-benzoquinone (1 a) reacts with azomethine ylide AY-A to give 2-methyl-5-phenylthio-2H-isoindole-4,7-dione (4 f). With 2-(N-methylanilino)-5-methyl-1,4-benzoquinone (1 b), the azomethine ylide AY-B undergoes cycloaddition to yield an inseparable mixture of 5a-methyl-8-(N-methylanilino)-2,3,5,5a,9a,9b-hexahydro-pyrrolo[2,1-a]1H-isoindole-6,9-dione (5 bI) and 9a-methyl-7-(N-methylanilino)-2,3,5,5a,9a,9b-hexahydropyrrolo[2,1-a]1H-isoindole-6,9-dione (5 bII). The structures of5 bI and5 bII were established on basis of two-dimensional-NMR-techniques. The mechanism of the cycloaddition of azomethine ylides to 1,4-quinones was studied on basis of cyclovoltammetric investigations. To determine the electron affinity of the isoindoledione derivatives4 a–f and5 a–b the peak potentials were measured by differential pulse polarography (DPP).

     

Spirocyclische 3-Oxazoline durch 1,3-dipolare Cycloaddition von Benzonitrilio-2-propanid mit 1,4-Chinonen

Spiro 3-Oxazolines from the 1,3-Dipolar Cycloaddition of Benzonitrilio-2-propanide and 1,4-Quinones On irradiation with light of wavelength 290–350 nm, 2,2-dimethyl-3-phenyl-2H-azirine (1b) reacts with 1,4-naphthoquinone to give the 1H-benzo [f]isoindol-4,9-dione (11) (Scheme 3) via cycloaddition of the benzonitrilio-2-propanide (2b) onto the quinone C, C-double bond. With 2-methyl- and 2,3-dimethyl-1,4-naphthoquinone, the nitrile ylide 2b undergoes cycloaddition preferentially onto the C, O-double bond of the quinone, leading to spiro-oxazolines 12 and 14 (Scheme 4). Steric as well as electronic effects can be discussed to explain the observed site selectivity of the cycloaddition. With the 1,4-benzoquinones 15a, 15b, 15d and 15f , nitrile ylide 2b undergoes the 1,3-dipolar cycloaddition exclusively onto the C, O-double bond. The corresponding spiro-oxazolines have been isolated in 17–32% yield. This contrasts with the previously reported results with benzonitrilipo-phenylmethanide (2a) , which undergoes cycloaddition to the C, C-double bond of 1,4-benzoquinones (cf. [1]). This difference in the site selectivity of the 1,3-dipolar cycloaddition can be explained with Houk's concept of LUMO-polarization, that is, the stronger nucleophilic dipol 2b polarizes the LUMO of a α,β-unsaturated carbonyl compound more efficient than the less nucleophilic 2a. This leads to a preference of the cycloaddition to the C, O-double bond in the case of 2b. With 2,3-dimethyl- (15c) and 2,3,5,6-tetramethyl-1,4-benzoquinone (15e) , nitrile ylide 2b undergoes C, O- as well as C, C-cycloaddition (Schemes 7 and 8).     

The reaction products of 2H-isoindole-4,7-dione derivatives with 2-aminobenzenethiol

From 2,3,4-Trisubstituted oxazolium-5-oxides and 2-methyl-, 2-phenyl- or 2-bromo-1,4-benzoquinone 1,2,3,5-tetrasubstituted 2H-isoindole-4,7-dione derivatives were prepared. These compounds were condensed with 2-aminobenzenethiol to produce 1,2,3-trisubstituted or 1,2,3,5-tetrasubstituted 4H-pyrrolo[3,4-a]phenothiazin-4-one derivatives. In the case of 1,2,3-trisubstituted 5-methyl-2H-isoindole-4,7-dione 1,2,3,5-tetrasubstituted 7-(2-mercaptophenyl)imino-2H-isoindole-4-one was obtained instead of the expected phenothiazinones.     

2H-Isoindol-4,7-dione durch Addition von Azomethinyliden an 1,4-Benzochinone

Summary A new approach to the synthesis of 2H-isoindole-4,7-diones is described. Heating -amino acids with carbonyl compounds generates azomethine ylides through the elimination of water and carbon dioxide. The ylides were captured by quinones forming 2H-isoindole-4,7-diones, 2,3,3a,7a-tetrahydro-1H-isoindole-4,7-diones and 2,3-dihydro-1H-pyrrolo[2,1-a]isoindole-6,9-diones. The structures were established on the basis of spectroscopy (NMR, mass).

Herrn Univ.-Prof. Dr. G. Zigeuner zum 70. Geburtstag gewidmet     

Photochemische Cycloadditionen von 3-Phenyl-2H-azirinen an Carbonsäurechloride. 35. Mitteilung über Photoreaktionen

Irradiation of 2, 3-diphenyl-2H-azirine ( 1a ) and 1-azido-1-phenyl-propene, the precursor of 2-methyl-3-phenyl-2H-azirine ( 1b ), in benzene, with a high pressure mercury lamp (pyrex filter) in the presence of acid chlorides yields the oxazoles 5a–d (Scheme 2). Photolysis of 2, 2-dimethyl-3-phenyl-2H-azirine ( 1c ) under the same conditions gives after methanolysis the 5-methoxy-2, 2-dimethyl-4-phenyl-3-oxazolines 7a, b, d , while hydrolysis of the reaction mixture leads to the formation of the 1, 2-diketones 8a, c, d (Scheme 4). The suggested reaction path for all these reactions is a 1, 3-dipolar cycloaddition of the photochemically generated benzonitrilemethylides 2 to the carbonyl double bond of the acid chlorides to give the intermediates 4 , followed by either elimination of hydrogen chloride or solvolysis (Schemes 2 and 4). Irradiation of 1c in the presence of acetic acid anhydride leads via the intermediate 9 to the 5-hydroxy-3-oxazoline 10 and the 5-methylidene-3-oxazoline 11 (Scheme 5).     

Functiaonalization of 2-(1-Cyclohexen-1-yl)aniline Derivatives

The reaction of 2-(1-cyclohexen-1-yl)aniline and -6-methylaniline with phthalic anhydride has afforded 2-(2-cyclohex-1-en-1-ylphenyl)- and 2-(2-cyclohex-1-en-1-ylphenyl)-6-methylphenyl)-1H-isoindole-1,3(2H)-diones. The reaction of the obtained isoindole-1,3-diones with bromine in dichloromethane in the presence of sodium bicarbonate has led to the formation of the product of pseudo-allylic halogenation. Replacement of the halogen atom by methoxy group has been performed by keeping 2-[2-(6-bromocyclohex-1-en-1-ylphenyl)-6-methylphenyl)]-1H-isoindole-1,3(2H)-dione in a methanolic solution in the presence of NaHCO₃. The reaction of 2-(2-cyclohex-1-en-1-yl-6-methylphenyl)-1H-isoindole-1,3(2H)-dione with molecular bromine in the presence of methanol has given a co-halogenation product, whereas the dibromination product has been obtained in the presence of octyl alcohol.

     

Reactions of 6-Amino-5-Cyano-3-Methyl-1,4-Diphenyl-1H 4H-Pyrano[2,3-C]Pyrazole and its Methanimidate

Reaction of 6-amino-5-cyano-3-methyl-1,4-diphenyl- 1H,4H-pyrano[2,3-c]pyrazole 1 with triethyl orthoformate in acetic anhydride gave its methanimidate 2, which reacts with primary aliphatic and aromatic amines to give 4,6-dihydro-3-methyl-1,4-diphenyl-6- (alkyl)pyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5(lH)- imine 3 and the starting compound 1 , respectively. Treatment of 1 with o-aminophenol gave 5-(2-benzoxalyl)- 1,4-dihydro-3-methyl-1,4-diphenylpyrano[2,3-c]pyrazol- 6-amine 9.     

Photochemische Cycloadditionen von 3-Phenyl-2H-azirinen mit Benzoyl-, Äthoxycarbonyl- und Vinylphosphonaten 34. Mitteilung über Photoreaktionen

The irradiation of the 3-phenyl-2H-azirines 1a–c in the presence of diethyl benzoylphosphonate ( 8 ) in cyclonexane solution, using a mercury high pressure lamp (pyrex filter), yields the diethyl (4, 5-diphenyl-3-oxazolin-5-yl)-phosphonates 9a–c (Scheme 3). In the case of 1b a mixture of two diastereomeric 3-oxazolines, resulting from a regiospecific but non-stereospecific cycloaddition of the benzonitrile-benzylide dipole 2b to the carbonyl group of the phosphonate 8 , was isolated. Benzonitrile-isopropylide ( 2a ), generated from 2,2-dimethyl-3-phenyl-2H-azirine ( 1a ), undergoes a cycloaddition reaction to the ester-carbonyl group of diethyl ethoxycarbonylphosphonate ( 15 ) with the same regiospecificity to give the 3-oxazoline derivative 16 (Scheme 5). The azirines 1a–c , on irradiation in benzene in the presence of diethyl vinylphosphonate ( 17 ) give non-regiospecifically the Δ¹-pyrrolines 13a–c and 14a–c (Scheme 6).     

Unkatalysierte sigmatrope 1,5-Wanderung von Acylgruppen bei der Thermolyse von 5-Acyl-5-methyl-1,3-cyclohexadienen

Uncatalyzed Sigmatropic 1,5-Shift of Acyl Groups in the Thermolysis of 5-Acyl-5-methyl-1,3-cyclohexadienes Four different 5-acyl-5-methyl-1,3-cyclohexadienes 1a–d (R = COOCH₃, COCH₃, COC₆H₅, CHO) have been shown to yield mixtures of 1,3-disubstituted cyclohexadienes 2–7 and 1,3-disubstituted aromatic product 8 upon thermolysis at 150–300° in solution and at 350–500° in the gas phase in a flow system. Two reaction pathways (A and B in Scheme 2) are considered for the rearrangement of the C-Skeleton. For the ester 1a ¹³C-isotopic substitution shows that products arise to 75–86% through a 1,5-sigmatropic shift of the methoxycarbonyl group ( A in Scheme 2) and to 14–25% through a sequence of reaction steps involving a 1,7-H-shift reaction in an acyclic intermediate ( B in Scheme 2). For the more reactive compounds 1b–d isomerization is assumed to follow the 1,5-sigmatropic pathway exclusively ( A in Scheme 2). A kinetic study yields the following sequence for the migration tendency of acyl groups toward sigmatropic 1,5-shift: COOCH₃ < COCH₃ < COC₆H₅ < CHO.     

Photoinduzierte 1, 3-dipolare Cycloaddition von 3-Phenyl-2H-azirinen an Azodicarbonsäure-diäthylester. 32. Mitteilung über Photoreaktionen

Irradiation of 2, 2-dimethyl-3-phenyl- ( 1a ), 2, 3-diphenyl-2H-azirine ( 1b ) or the azirine-precursors 1-azido-1-phenyl-propene ( 2a ) and 1-azido-1-phenyl-ethylene ( 2b ), respectively, in benzene in the presence of azodicarboxylic acid diethylester, yields the corresponding 1, 2-carbethoxy-3-phenyl-Δ³-1, 2, 4-triazolines 4a–d (Scheme 1). Refluxing 4 ( a, c or d ) in 0, 2–0, 4M aqueous ethanolic potassium hydroxide leads to the formation of the 1-carbethoxy-3-phenyl-Δ²-1, 2, 4-triazolines 6 ( a, c or d ). Under the same conditions 4b is converted to 3, 5-diphenyl-1, 2, 4-triazole ( 7b , Scheme 2). In 10M aqueous potassium hydroxide solution heating of either 4 ( c or d ) or 6 ( c or d ) yields the 3-phenyl-1, 2, 4-triazoles 7 ( c or d ). Photolysis of 1-carbethoxy-5, 5-dimethyl-3-phenyl-Δ²-1, 2, 4-triazoline ( 6a ) in benzene in the presence of oxygen and trifluoroacetic acid methylester gives the 5-methoxy-2, 2-dimethyl-4-phenyl-5-trifluoromethyl-3-oxazoline ( 13 , Scheme 5). 5, 5-Dimethyl-3-phenyl-1, 2, 4-triazole seems to be the intermediate, which on losing nitrogen gives the benzonitrile-isopropylide ( 3a ).     

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

The purely aliphatic 2,3-dipropyl-2H-azirine ( 1 ) reacts on irradiation with a mercury high-pressure lamp through a Vycor filter with methyl trifluoroacetate or acetone to form 3-oxazolines 3a, b (65%) resp. 4 (14%) (Scheme 1). 9-Azabicyclo[6.1.0]non-1(9)-ene ( 5 ) on irradiation in the presence of the dipolarophiles methyl trifluoroacetate, methyl difluoroacetate, 1,1,1-trifluoro-propanone and acetone behaves in a similar way, whereby the corresponding bicyclic 3-oxazolines 7–10 result in yields of 60–20% (Scheme 2). By analogy with the photochemical behaviour of 3-aryl-2H-azirines it is assumed that nitrile-ylides 2 resp. 6 represent intermediates. In fact irradiation of 2,3-dipropyl-2H-azirine ( 1 , λ_max 239 nm, ? 240) at ?196° with light of wavelength 245 nm in a hydrocarbonglass gives rise to a pronounced maximum at 280 nm, for which an ? of ? 15000 can be estimated. The quantum yield for the formation of nitrile-methylide 2 is 0,8. Irradiation of the dipole 2 at ?196° or warming to ?150° causes the maximum at 280 nm to disappear.     

Zur Photodimerisierung von 3-Phenyl-2H-azirinen. Vorläufige Mitteilung

Irradiation of 3-phenyl-2H-azirine ( 2 ) in benzene solution with a high-pressure mercury lamp yields 4,5-diphenyl-1,3-diazabicyclo[3,1,0]hex-3-ene ( 4 ) and not 3-phenylimino-4-phenyl-1-azabicyclo[2,1,0]pentane ( 1 ), as had been reported previously by others [2]. 2-Methyl-3-phenyl-2H-azirine ( 3 ) yields on irradiation a 2:1 mixture of 2-exo, 6-exo- and 2-exdo, 6-exo-dimethyl-4,5-diphenyl-1,3-diazabicyclo[3,1,0]hex-3-ene (2-exo,6-exo- and 2-endo, 6-exo- 5 ). Irradiation of 2,3-diphenyl-2H-azirine ( 8 ) leads to the formation of 2,4,5-triphenyl-imidazole ( 9 ) and tetra-phenylpyrazine ( 10 ). The suggested reaction path for the generation of 9 and 10 is shown in Scheme 2.     

Synthesis of polycyclic pyridazinediones as chemiluminescent compounds

Reactions of 1,3-disubstituted 5-aminopyrazole-4-carbonitrile derivatives 3a-o with dimethyl acetylenedicarboxylate in the presence of potassium carbonate in dimethyl sulfoxide gave the corresponding dimethyl 1,3-disubstituted pyrazolo[3,4-b]pyridine-5,6-dicarboxylates 4a-o which were allowed to react with excess hydrazine hydrate under ethanol refluxing conditions followed by heating at 250-300° to give 1,3-disubstituted 4-amino-1H-pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyridazine-5,8(6H,7H)-diones 7a-s in good yields. Similarly, 1,3-disubstituted 4-hydroxy-1H-pyrazolo[4′3′:5,6]pyrido[2,3-d]pyridazine-5,8(6H,7H)-diones 10a-c were obtained from alkyl 1,3-disubstituted 5-aminopyrazole-4-carboxylates 8a-c . These tricyclic pyridazine derivatives were alternatively synthesized from 4-hydroxypyrrolo[3,4-e]pyrazolo[3,4-b]pyridine-5,7-diones 13a-c prepared by reactions of 5-aminopyrazoles (8e-g) with methyl 1-methyl-4-methylthio-2,5-dioxo-1H-pyrrole-3-carboxylate (11a) followed by the Gould/Jacobs reaction. 1-Methyl-4-methylthio-2,5-dioxo-1H-pyrrole-3-carbonitrile smoothly reacted with 2-aminobenzimidazoles to give the corresponding 5-amino-3-methyl-1H-pyrrolo[3′4′:4,5]pyrimido[1,2-a]benzimidazole-1,3(2H)-diones 16a-e , which were readily converted to the desired 12-aminopyridazino[4′,5′:4,5]pyrimido-[1,2-a]benzimidazole-1,4(2H,3H)-diones 17a-e in good yields. Other pyridazinopyrimidine derivatives were also obtained by the reaction of the corresponding 2-aminoheterocycles with the maleimide in good yields. Substituted anilines reacted 11b in refluxing methanol to give the corresponding methyl 4-phenylamino-1-methyl-2,5-dioxo-1H-pyrrole-3-carboxylates 25a-e which were converted in good yields to 2-methylpyrrolo[3,4-b]quinoline derivatives 26a-e by heating in diphenyl ether. Reaction of 26a-c with hydrazine hydrate gave 10-hydroxypyridazino[4,5-b]quinoline-1,4(2H,3H)-diones 27a-e in good yields. The desired 10-aminopyridazino[4,5-b]pyridazine-1,4(2H,3H)-diones 30a-e were obtained in good yields by the chlorination of 4a-e with phosphorus oxychloride followed by aminolysis with 28% ammonium hydroxide. Some pyridazino[4,5-a][2.2.3]cyclazine-1,4(2H,3H)-diones 37a,b as luminescent compounds were synthesized via several steps from indolizine derivatives. The key intermediates, dimethyl 6-dimethylamino[2.2.3]cyclazine-1,2-dicarboxylates 34, 36 , were synthesized by the [8 + 2] cycloaddition reaction of the corresponding 7-dimethylaminoindolizines 33, 35 with dimethyl acetylenedicarboxylate in the presence of Pd-C in refluxing toluene. Some were found to be more efficient than luminol in light production. 4-Amino-3-methylsufonyl-1-phenyl-1H-pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyridazine-5,8(6H,7H)-dione (7r) , 10-hydroxypyridazino[4,5-b]-quinoline-1,4(2H,3H)-diones 27a-e , and 10-aminopyridazino[4,5-b]quinoline-1,4(2H,3H)-diones 30a-e showed the greatest chemiluminescence intensity in the presence of hydrogen peroxide peroxidase in a solution of phosphate buffer at pH 8.0.     

Ringerweiterungen und Ringverengungen bei der Umsetzung von 1, 3-Oxazolidin-2, 4-dionen und 1, 3-Thiazoiidin-2, 4-dion mit 3-Amino-2H-azirinen

Ring Enlargements and Ring Contractions in the Reaction of 1, 3-Oxazolidine-2, 4-diones and l, 3-Thiazolidine-2, 4-dione with 3-Amino-2H-azirines The reaction of 3-amino-2H-azirines 1 and 1, 3-oxazolidine-2, 4-diones 2 in MeCN at room temperature leads to 3, 4-dihydro-3-(2-hydroxyacetyl)-2H-imidazol-2-ones 3 in good yield (Scheme 2, Table 1). A reaction mechanism proceeding via ring enlargement of the bicyclic zwitterion A to give B, followed by transannular ring contraction to C, is proposed for the formation of 3 . This mechanism is in accordance with the result of the reaction of 2a and the ¹⁵N-labelled 1a *: in the isolated product 3a *, only N(3) is labelled (Scheme 1). The analogous reaction of 1 and 1, 3-thiazolidine-2, 4-dione ( 5 ) is more complex (Schemes 4 and 5, Table 2). Besides the expected 3, 4-dihydro-3-(2-mercaptoacetyl)-2H-imidazol-2-ones 7, 5-amino-3, 4-dihydro-2H-imidazol-2-ones of type 8 and/or N-(1, 4-thiazin-2-ylidene)ureas 9 are formed. In the case of 2-(dimethylamino)-1-azaspiro[2. 3]hex-1-ene ( 1d ), the postulated eight-membered intermediate 6d could be isolated. Its structure as well as that of 9f has been determined by X-ray structure analysis. A reaction mechanism for the formation of the 1, 4-thiazine derivatives of type 9 is proposed in Scheme 6.     

Five-membered 2,3-dioxoheterocycles: LXIV. Reactions of 1-methyl-3,4-dihydroisoquinolines with 5-arylfuran-2,3-diones and (Z)-alkyl 4-aryl-2-hydroxy-4-oxobut-2-enoates. Crystal and molecular structure of (2Z,5Z)-3-hydroxy-5-{8,8-dimethyl-2,3,8,9-tetrahydro[1,4]dioxino[2,3-g]isoquinolin-6(7H)-ylidene}-1-phenylpent-2-ene-1,4-dione

5-Arylfuran-2,3-diones and (Z)-alkyl 4-aryl-2-hydroxy-4-oxobut-2-enoates react with 3,3-dialkyl-1-methyl-3,4-dihydroisoquinolines to give (2Z,5Z)-1-aryl-3-hydroxy-5-[3,3-dialkyl-3,4-dihydroisoquinolin-1(2H)-ylidene]pent-2-ene-1,4-diones whose structure has been proved by XRD analysis.     

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

Irradiation (280–350 nm light) of a benzene solution of 3-phenyl-2H-azirines 1a – e in the presence of carboxylate esters, whose carbonyl groups are activated by electron withdrawing groups situated in the acyl or alkyl moiety, produces 5-alkoxy-3-oxazolines (Tab. 1 and 4, Scheme 2) isolated in 18–82% yield. These heterocycles undoubtedly originate by regiospecific addition of the ester carbonyl group to the azirine-derived benzonitrile-methylide ‘dipole’ (Scheme 1). The 5-(2,′ 2′, 2′-trifluoroethoxy)-3-oxazolines, derived from 2′, 2′, 2′-trifluoroethyl carboxylic esters, on treatment with methanolic hydrogen chloride at low concentration, are smoothly transformed into the corresponding 5-methoxy-3-oxazolines (e.g. 16 → 17 , Tab. 5). Utilizing this process, various hitherto relatively unknown 9. 5-alkoxy-3-oxazolines become accessible. The constitution of the adducts is based essentially on spectral data. The structure of trans-5-methoxy-2,4-diphenyl-5-trifluoromethyl-3-oxazoline (trans- 14 ), the addition product of methyl trifluoroacetate and the benzonitrile-benzylide from 2,3-diphenyl-2H-azirine ( 1d ), was determined by X-ray crystallography (Section 5). Benzonitrile-isopropylide ( 22 ), resulting from the photochemical transformation of 2,2-dimethyl-3-phenyl-2H-azirine ( 1a ), also reacts with S-methyl thiobenzoate to give 2,2-dimethyl-5-methylthio-4,5-diphenyl-3-oxazoline ( 26 ). Ethyl cyanoacetate protonates predominantly the dipolar species derived from 1a at the nitrile C-atom and yields after work-up ethyl α-cyano-cinnamate ( 29 ) and ethyl isopropylidene-cyanoacetate ( 30 ) (Scheme 4). The relative rate of addition (k_rel) of benzonitrile-isopropylide ( 22 ) to methyl α-haloacetates and dimethyl oxalate was determined by competition experiments (Section 6). Log k_rel correlated satisfactorily (r = 0.97) with the pK_a of the acide derived from the ester reactant: log k_rel = ? 1.72 pK_a + 2.58 or with Taft's substituent constants σ*: log k_rel = 2.06 σ* ? 4.11 [k_rel(methyl dichloroacetate) = 1; Section 7.1]. On the basis of the results obtained, the mode of reaction of the so-called benzonitrile-methylide ‘dipole’ is discussed and a model for the transition state of addition of ester-carbonyl groups is proposed that accounts for the observed regiospecifity and steroselectivity.     

Reactions of 3-hydrazino-5,6-diphenyl-1,2,4-triazine with 4-arylidene-2-phenyl-5(4H)-oxazolones and 4-benzylidene-3-methyl-5(4H)-isoxazolone

3-Hydrazino-5,6-diphenyl-1,2,4-triazine reacts with 4-arylidene-2-phenyl-5(4H)-oxazolones in toluene to give substituted acrylic acid hydrazides, and in glacial acetic acid to give substituted imidazolones. On the other hand the hydrazinotriazine reacts with 4-benzylidene-3-methyl-5(4H)-isoxazolone, probably via a 1,4 addition reaction followed by an elimination reaction, to give benzaldehyde 5,6-diphenyl-1,2,4-triazin-3-ylhydrazone and 3-methyl-5(4H)-isoxazolone.     

Tieftemperaturbestrahlungen von 3-Phenyl-2H-azirinen

2, 2, 3-Triphenyl-2H-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 ( 1a ) 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 at room temperature in the presence of TFEM (scheme 1 and table 1). Modification of the previously described experiment, in which the maximum at 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 1a , was calculated. These experiments have shown that irradiation of triphenylazirine 4a leads to the dipole 1a , which can be reversed photochemically – but not tharmally – into azirine 4a. 1a reacts at less than ?160° with TFEM to give adduct 6a . The results which were obtained with triphenylazirine 4a could be correspondingly obtained with 2, 3-diphenyl-2H-azirine 4b (Fig. 3, scheme 2 and table 2). The dipole 1b showed two UV.-maxima at 330 nm (ε = 17, 500) and 343 nm (ε = 21, 000). Later experiments established, that the two maxima belonged to a single dipole species. The dipole 1c obtained upon irradiation of 2, 2-dimethyl-3-phenyl-2H-azirine ( 4c ) in DMBP at ?190°, appears to absorb in the same region as the azirine 4c . The presence of the dipole 1c was univocally established by low temperature trapping experiments with TFEM. The dipole 1a showed no ESR.-spectrum characteristic for a triplet state. We assume therefore, that 1a is in a singlet state. Photolysis of oxazolinone 7 at ?190° in DMBP led to the dipole 1a with loss of CO₂. 1a recombines apparently in considerable amount with the CO₂ trapped in the matrix to give starting oxazolinone 7 because the 350 nm-maximum of 1a appeared with low extinction. Irradiation with light of 366 nm into this matrix produccd triphenylazirine 4a . Low temperature trapping experiments with TFEM led to small amounts of 5-methoxy-5-trifluormethyl-triphenyl-3-oxazolinc ( 6a ).