Die Struktur des Adduktes aus 3-Dimethylamino-2,2-dimethyl-2H-azirin und 3-Methyl-2,4-diphenyl-1,3-oxazolium-5-olat. Vorläufige Mitteilung

Structure of the adduct from 3-dimethylamino-2,2-dimethyl-2H-azirine and 3-methyl-2,4-diphenyl-1,3-oxazolium-5-olate 3-Dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) reacts with 3-methyl-2,4-diphenyl-1,3-oxazolium-5-olate ( 5a ) to give a 1:1 adduct ( 7 ) in a 88% yield. Its crystal structure has been determined by X-ray analysis (direct methods) and refined with 1056 structure amplitudes to R = 0,032. The crystal system is monoclinic, space group P2₁/c, with unit cell dimensions a = 10.663, b = 9,828, c = 18,592 Å, and β = 90,63°. It is obvious that 4-dimethylamino-5,5-dimethyl-2-[α-(N-methyl-benzamido)benzyliden]-Δ³-1,3-oxazoline ( 7 ) arises from an addition of 1 to the valence-polaromeric ketene form 5b of the mesoionic oxazolone 5a (Scheme 3).     

Die Struktur einer stabilen dipolaren Verbindung aus 2,2-Dimethyl-3-dimethylamino-2H-azirin und Benzoylisothiocyanat. Vorläufige Mitteilung

Structure of a Stable Dipolar Compound from 2,2-Dimethyl-3-dimethylamino-2H-azirine and Benzoylisothiocyanate. Benzoylisothiocyanate and 2,2-dimethyl-3-dimethylamino-2H-azirine ( 1 ) react to given the dipolar compound 4,4-dimethyl-2-thiazolin-5-dimethylimminium-2-benzcarboxamidate ( 2 ), whose structure has been proved by X-ray analysis. Compound 2 , upon addition of water, yields the thiourea derivative 3 , whereas by acid catalyzed hydrolysis the thiazolinone derivative 4 is formed. The dipolar structure 2 is also existent in organic solvents like dimethylsulfoxide or chloroform.     

Additionsreaktion von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit Phenylisothiocyanat

Reaction of 3-Dimethylamino-2,2-dimethyl-2H-azirine with Phenyl Isothiocyanate In contrast to the reactions of 3-dimethylamino-2,2-dimethyl-2H-azirine ( 1a ) with various isothiocyanates, leading to thiazoline derivatives, the reaction of 1a with phenyl isothiocyanate at room temperature gives 5,5-dimethyl-3-phenyl-Δ¹-imidazolin-4-dimethyliminium-2-thiolate ( 9 , Scheme 2). The structure of 9 is deduced from spectral data and reactions of this zwitterionic compound (Schemes 2 and 4).     

Synthese und Reaktionen 8-gliedriger Heterocyclen aus 3-Dimethylamino-2,2-dimethyl-2H-azirin und Saccharin bzw. Phthalimid

Synthesis and Reactions of 8-membered Heterocycles from 3-Dimethylamino-2,2-dimethyl-2H-azirine and Saccharin or Phthalimide 3-Dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) reacts at 0-20° with the NH-acidic compounds saccharin ( 2 ) and phthalimide ( 8 ) to give the 8-membered heterocycles 3-dimethylamino-4,4-dimethyl-5,6-dihydro-4 H-1,2,5-benzothiadiazocin-6-one-1,1-dioxide ( 3a ) and 4-dimethylamino-3,3-dimethyl-1,2,3,6-tetrahydro-2,5-benzodiazocin-1,6-dione ( 9 ), respectively. The structure of 3a has been established by X-ray (chap. 2). A possible mechanism for the formation of 3a and 9 is given in Schemes 1 and 4. Reduction of 3a with sodium borohydride yields the 2-sulfamoylbenzamide derivative 4 (Scheme 2); in methanolic solution 3a undergoes a rearrangement to give the methyl 2-sulfamoyl-benzoate 5 . The mechanism for this reaction as suggested in Scheme 2 involves a ring contraction/ring opening sequence. Again a ring contraction is postulated to explain the formation of the 4H-imidazole derivative 7 during thermolysis of 3a at 180° (Scheme 3). The 2,5-benzodiazocine derivative 9 rearranges in alcoholic solvents to 2-(5′-dimethylamino-4′,4′-dimethyl-4′H-imidazol-2′-yl) benzoates ( 10 , 11 ), in water to the corresponding benzoic acid 12 , and in alcoholic solutions containing dimethylamine or pyrrolidine to the benzamides 13 and 14 , respectively (Scheme 5). The reaction with amines takes place only in very polar solvents like alcohols or formamide, but not in acetonitrile. Possible mechanisms of these rearrangements are given in Scheme 5. Sodium borohydride reduction of 9 in 2-propanol yields 2-(5′-dimethylamino-4′,4′-dimethyl-4′H-imidazol-2′-yl)benzyl alcohol ( 15 , Scheme 6) which is easily converted to the O-acetate 16 . Hydrolysis of 15 with 3N HCl at 50° leads to an imidazolinone derivative 17a or 17b , whereas hydrolysis with 1N NaOH yields a mixture of phthalide ( 18 ) and 2-hydroxymethyl-benzoic acid ( 19 , Scheme 6). The zwitterionic compound 20 (Scheme 7) results from the hydrolysis of the phthalimide-adduct 9 or the esters 11 and 12 . Interestingly, compound 9 is thermally converted to the amide 13 and N-(1′-carbamoyl-1′-methylethyl)phthalimide ( 21 , Scheme 7) whose structure has been established by an independent synthesis starting with phthalic anhydride and 2-amino-isobutyric acid. However, the reaction mechanism is not clear at this stage.     

Additionsreaktionen von 3-Dimethylamino-2,2-dimethyl-2H-azirin an Phenylisocyanat und Diphenylketen

Addition Reaction of 3-Dimethylamino-2,2-dimethyl-2H-azirine with Phenylisocyanate and Diphenylketene 3-Dimethylamino-2,2-dimethyl-2H-azirine ( 1a ) reacts with carbon disulfide and isothiocyanates with splitting of the azirine N(1), C(3)-double bond to give dipolar, fivemembered heterocyclic 1:1 adducts. In some cases, these products can undergo secondary reactions to yield 1:2 and 1:3 adducts. In this paper it is shown that the reaction of 1a with phenylisocyanate also takes place by cleavage of the N(1), C(3)-bond, whereas with diphenylketene N(1), C(2)-splitting is observed. The reaction of 1a and phenylisocyanate in hexane at room temperature yields the 1:3 adduct 2 in addition to the trimeric isocyanate 3 (Scheme 1). A mechanism for the formation of 2 is given in Scheme 5. Hydrolysis experiments with the 1:3 adduct 2 , yielding the hydantoins 4–6 and the ureas 7 and 8 (Schemes 3 and 5), show that the formation of this adduct via the intermediates d , e and f is a reversible reaction. The aminoazirines 1a and 1b undergo an addition reaction with diphenylketene to give the 3-oxazolines 14 (Scheme 8), the structure of which has been established by spectral data and oxidative degradation of 14a to the 3-oxazolin-2-one 15 (R¹ ? R² ? CH₃, Scheme 9).     

Heterocyclole als Zwischenprodukte einer neuen, überraschenden Umlagerung bei der Reaktion von 3-(Dimethylamino)-2,2-dimethyl-2H-azirin mit monosubstituierten Parabansäuren. Vorläufige Mitteilung

Cyclols as Intermediates in the Reaction of 3-(Dimethylamino)-2,2-dimethyl-2H-azirine with Monosubstituted Parabanic Acids; a New and Unexpected Rearrangement The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) with N-methylparabanic acid ( 4 ) in 2-propanol at room temperature gives the cyclol 5 in 97% yield. In acetonitrile solution 5 rearranges to the imidazoline derivative 6 (Scheme 2). The structures of the unexpected products 5 and 6 have been established by X-ray crystallography.     

Photoinduzierte Cycloadditionen von 2,2-Dimethyl-3-phenyl-2H-azirin an Nitrile und «push-pull»-Olefine. 43. Mitteilung über Photoreaktionen

Photoinduced Cycloadditions of 2,2-Dimethyl-3-phenyl-2H-azirine with Nitriles and ‘push-pull’ Olefines. Electron deficient nitriles of the type 5a–e in contrast to nonactivated nitriles undergo regiospecific [2+3]cycloadditions to benzonitrile isopropylide ( 2b ), which was generated in situ by irradiation of 2,2-dimethyl-3-phenyl-2H-azirine ( 1b ), to yield the 2H-imidazole derivatives 6a – e (Scheme 2). The structure of the photoproducts was mainly deduced from ¹³C-NMR. and mass spectrometry. Whereas normal olefins or enolethers do not react with 2b , push-pull olefins of the type 10a – d readily undergo the cycloaddition to give the 3-alkoxy-5,5-dimethyl-2-phenyl-1-pyrrolines 11a – d (Scheme 3 and 4). The structure of the photoproducts 11a – d indicates that the regiospecificity of the cycloaddition corresponds to that of acrylonitriles and acrylesters with 2b .     

Struktur des Hydrazinolyseproduktes von N-(3-Oxo-1-isoindolinyliden)-alanin-äthylester

Hydrazinolysis of N-(3-Oxo-1-isoindolinyliden)alanin Ethyl Ester, Structure of the Product Treatment of N-(3-oxo-1-isoindolinyliden)alanin ethyl ester (6) with hydrazine hydrate leads to 4-methyl-2,3,4,6-tetrahydro[1,2,4]triazino[3,4-a]isoindole-3, 6-dione ( 8 , Scheme 3) and not to the previously postulated 6-hydroxy-2-methyl-2,3-dihydro-imidazo [2,1-a]phthalazin-3-one ( 7 , cf. [2]). The structure of 8 has been established by an independent synthesis as well as by the X-ray analysis of the reaction product 11 from 8 and 3-dimethylamino-2,2-dimethyl-2 H-azirine ( 1 , Scheme 4). A reaction mechanism for the formation of 8 from 6 is suggested in Scheme 5.     

Reaktionen von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit Phenolen und Halogenaromaten

Reactions of 3-dimethylamino-2,2-dimethyl-2H-azirine with phenols and aryl halides The reactions of 3-dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) with phenols are described in chap. 1. The azirine 1 reacts with the 2-formyl- and 2-acetylphenols 5 – 8 to yield the N′-methylidene derivatives of 2-amino-N,N-dimethyl-isobutyramide 9 - 12 (Scheme 2, tautomeric form b ). These products are in equilibrium with the tautomeric quinoide forms 9a-12a . Under similar conditions 4-hydroxybenzaldehyde did not react with 1 . Reaction of 1 with 4-hydroxycoumarine ( 13 ) gives the 4-amino-coumarine 14 (Scheme 2). The mechanism of these reactions is analogous to the previously reported one for the reaction of 1 with cyclic enolisable 1,3-diketones [2] [3]. Activated phenols with pK_a-values < 8, e.g. 2- and 4-nitrophenol, 2,4-dinitrophenol and pentachlorophenol, undergo addition reactions with 1 in boiling benzene solution to give the aniline derivatives 15 - 18 (Scheme 3). A reaction mechanism is given in Scheme 3: after protonation of the azirine 1 followed by attack of the phenolate ion at the amidinium-C-atom, the intermediate of type e undergoes a rearrangement to the spiro-Meisenheimer complexes of type f . Ring opening leads to 15 – 18 . A similar reaction is observed for 2,4-dinitro-thiophenol and 1 , giving 2-(N′-(2,4-dinitrophenyl)amino)-N,N-dimethyl-isobutyrothioamide ( 19 ). The azirine 1 reacts with the more acidic 2,4,6-trinitrophenol (picric acid) to yield 3,3,6,6-tetramethylpiperazine-2,5-bis(N,N-dimethyliminium) dipicrate ( 21 , Scheme 4). The methacrylamidinium salt 22 is the only product (97% yield) in the reaction of 8-hydroxy-5,7-dinitroquinoline and 1 in acetonitrile solution. The reaction of 1 with picric acid can be explained in a similar way as the previously reported one with strong acids (cf. Scheme 1, [1] [3] [5]). An alternative mechanism without formation of the 1-aza-allylcation c is postulated in Scheme 5, together with a mechanism which could explain the exclusive formation of 22 in the reaction of 1 with 8-hydroxy-5,7-dinitroquinoline. In chap. 2 a few reactions of the azirine 1 with aryl halides are reported. In the reaction with 2,4-dinitrofluorobenzene it is shown by UV. and NMR., that m , n and o are intermediates (Scheme 6). Working up the reaction mixture with water, hydrogen sulfide or benzylamine leads to the aniline derivatives 17 , 19 and 26 , respectively. With picryl chloride and 8-hydroxy-5,7-dinitroquinoline the azirine 1 undergoes a nucleophilic aromatic substitution to afford the intermediates p and q , which via deprotonation and ring opening give acrylamidine derivatives ( 27 and 29 , Scheme 7 and 8). The steric hindrance in p and q between the aziridine ring and the two groups in o-position could be the reason for the different behaviour of the intermediates n and p or q (cf. Schemes 6 and 8).     

3-(Dimethylamino)-2,2-dimethyl-2H-azirin als Aib-Äquivalent: Synthese von Aib-Oligopeptiden

3-(Dimethylamino)-2,2-dimethyl-2H-azirine as an Aib Equivalent; Synthesis of Aib Oligopeptides 3-(Dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) reacts with carboxylic acids at 0–25° to give 2-acylamino-N,N,2-trimethylpropionamides ( = 2-acylamino-N,N-dimethylisobutyramide, acyl-Aib-NMe₂) in excellent yields (Scheme 2 and 3). Examples of α-amino-, α-hydroxy-, and α-mercapto-carboxylic acids are given. On treatment with HCl in toluene, the terminal dimethylamide group is selectively converted to the corresponding carboxylic acid (→acyl-Aib) via an amide cleavage (Scheme 4 and 5); 1,3-oxazol-5(4H)-ones are intermediates of this amide hydrolysis. This reaction sequence has been used for the extension of peptide chains (Scheme 6). The synthesis of Aib-oligopeptides using this methodology is described (Scheme 8).     

Reaktion von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit Barbitursäure

Reaction of 3-Dimethylamino-2,2-dimethyl-2H-azirine with Barbituric Acid The reaction of 3-dimethylamino-2,2-dimethyl-2H-azirine (1) with barbituric acid (4) in dimethyl formamide at room temperature yields a mixture of several compounds. The two main products 5 and 6 have been isolated in 40 and 10% yield, respectively, and their structures established by X-ray analysis. In Schemes 4–6 reaction mechanisms for the formation of 5 and 6 are postulated, the first step beeing either a C- or an N-alkylation of barbituric acid. Reduction of 5 and 6 with NaBH₄ in ethanol at room temperature yields 6,6-dimethyl-1,5,6,7-tetrahydro-pyrrolo[2,3-d]pyrimidin-2,4(3H)-dione (7) and 3,3-dimethyl-2,3-dihydro-imidazo[1,2-c]pyrimidin-5,7(1H, 6H)-dione (8) in 38 and 48% yield, respectively. Treatment of 6 with 3N aqueous NaOH at room temperature gives 3,3-dimethyl-imidazo[1,2-c]pyrimidin-2,5,7 (1H, 3H, 6H)-trione (9) in 51% yield (Scheme 3).     

3-(Dimethylamino)-2,2-dimethyl-2H-azirin als α-Aminoisobuttersäure(Aib)-Äquivalent: Cyclische Depsipeptide durch direkte Amid-Cyclisierung

3-(Dimethylamino)-2,2-dimethyl-2H,-azirine as an α-Aminoisobutyric-Acid (Aib) Equivalent: Cyclic Depsipeptides via Direct Amid Cyclization In MeCN at room temperature, 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) and α-hydroxycarboxylic acids react to give diamides of type 8 (Scheme 3). Selective cleavage of the terminal N,N-dimethylcarboxamide group in MeCN/H₂O leads to the corresponding carboxylic acids 13 (Scheme 4). In toluene/Ph SH , phenyl thioesters of type 11 are formed (see also Scheme 5). Starting with diamides 8 , the formation of morpholin-2,5- diones 10 has been achieved either by direct amide cyclization via intermediate 1,3-oxazol-5(4H)-ones 9 or via base-catalyzed cyclization of the phenyl thioesters 11 (Scheme 3). Reaction of carboxylic acids with 1 , followed by selective amide hydrolysis, has been used for the construction of peptides from α-hydroxy carboxylic acids and repetitive α-aminoisobutyric-acid (Aib) units (Scheme 4). Cyclization of 14a, 17a , and 20a with HCI in toluene at 100° gave the 9-, 12-, and 15-membered cyclic depsipeptides 15, 18 , and 21 , respectively.     

Reaktion von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit 6-Methyluracil; Kristallstruktur der Reaktionsprodukte

Reaction of 3-Dimethylamino-2,2-dimethyl-2H-azirine with 6-Methyluracil; Crystal Structure of the Products The reaction of 3-dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) with 6-methyl-uracil ( 4 ) in 2-propanol at 80° yields the 4H-imidazoje derivative 5 as the main product. This reaction is similar to the previously reported ones with heterocyclic compounds containing the sequence NH? CO? NH? CO. In the presence of water, 5 is easily hydrolyzed to 6 . The structures of 5 and 6 have been established by X-ray crystallography.     

1,3-Dipolare Cycloadditionen von 2-(Benzonitrilio)-2-propanid mit 4,4-Dimethyl-2-phenyl-2-thiazolin-5-thion und Schwefelkohlenstoff

1,3-Dipolar Cycloadditions of 2-(Benzonitrilio)-2-propanide with 4,4-Dimethyl-2-phenyl-2-thiazolin-5-thione and Carbon Disulfide Irradiation of 2,2-dimethyl-3-phenyl-2H-azirine ( 11 ) in the presence of 4,4-dimethyl-2-phenyl-2-thiazolin-5-thione ( 7 ) yields a mixture of the three (1:1)-ad-ducts 8 , 12 and 13 (Schemes 3 and 6). The formation of 8 and 12 can be explained by 1,3-dipolar cycloaddition of 2-(benzonitrilio)-2-propanide ( 1b ) to the C, S-double bond of 7. Photochemical isomerization of 12 leads to the third isomer 13 (Schemes 3 and 7). Photolysis of the azirine 11 in the presence of carbon disulfide gives a mixture of two (2:l)-adducts, namely 12 and 13 (Scheme 4). A reaction mechanism via the intermediate formation of the 3-thiazolin-5-thione b is postulated. The structure of the heterocyclic spiro compound 13 has been established by single-crystal X-ray structure determination (cf. Fig. 1 and 2).     

Eine überraschende Ringerweiterung von 3-(Dimethylamino)-2,2-dimethyl-2H-azirin zu 4,5-Dihydropyridin-2(3H)-on-Derivaten

An Unexpected Ring Enlargement of 3-(Dimethylamino)-2,2-dimethyl-2H-azirine to 4,5-Dihydropyridin-2(3H)-one Derivatives The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1a ) and 4,4-disubstituted 2-(trifluoromethyl)-1,3-oxazol-5(4H)-ones 7 in MeCN at 70° afforded 5-(dimethylamino)-3,6-dihydropyrazin-2(1H)-ones 10 (Scheme 4), whereas no reaction could be observed between 1a and 2-allyl-4-phenyl-2-(trifluoromethyl)-1,3-oxazol-5(2H)-one ( 8a ) or 4,4-dibenzyl-2-phenyl-1,3-oxazol-5(4H)-one ( 9 ). The formation of 10 is rationalized by a mechanism via nucleophilic attack of 1a onto 7 . The failure of a reaction with 9 shows that only activated 1,3-oxazol-5(4H)-ones bearing electron-withdrawing substituents do react as electrophiles with 1a . The amino-azirine 1a and 2,4-disubstituted 1,3-oxazol-5(4H)-ones 2b – e in refluxing MeCN undergo a novel ring enlargement to 4,5-dihydropyridin-2(3H)-ones 11 (Scheme 5). Several side products were observed in these reactions. Two different reaction mechanisms for the formation of 11 are proposed: either 1a undergoes a nucleophilic addition onto the open-chain ketene tautomer of 2 (Scheme 6), or 2 reacts as CH-acidic compound (Scheme 7).     

Ring-Transformation von Imidazolidin–2,4-dionen ( = Hydantoinen) zu 4H-Imidazolen bei der Umsetzung mit 3-(Dimethylamino)-2,2-dimethyl-2H -azirin

Ring Transformation of Imidazolidine-2,4-diones ( = Hydantoins) to 4H-Imidazoles in the Reaction with 3-(Dimethylamino)-2,2-dimethyl-2H-azirines At ca. 70°, 3-(dimethylamino)-2,2-dimethyl-2H -azirine ( 1 ) and 5,5-disubstituted hydantoins 4 in MeCN or i-PrOH give 2-(1-aminoalkyl)-5-(dimethylamino)-4,4-dimethyl-4H -imidazoles 5 in good yield (Scheme 2). These products are decarboxylated 1:1 adducts of 1 and 4 . A reaction mechanism is suggested in analogy to the previously reported reactions of 1 and NH-acidic heterocycles containing the CO? NH? CO? NH moiety (Scheme 5). The formation of ureas 6 and 7 can be rationalized by trapping the intermediate isocyanate F by an amine. No reaction is observed between 1 and 1,5,5- or 3,5,5-trisubstituted hydantoins in refluxing MeCN or i-PrOH, but an N-isopropylation of 1,5,5-trimethylhydantoin ( 8b ) occurs in the presence of morpholine (Scheme 3). The reaction of the bis(azirine)dibromozink complex 11 and hydantoines 4 in refluxing MeCN yields zink complexes 12 of the corresponding 2-(1-aminoalkyl)-4H -imidazoles 5 (Scheme 4).     

Reaktionen von 3-Dimethylamino-2,2-dimethyl-2H-azirin mit. NH-aciden Heterocyclen; Synthese von 4H-imidazolen

Reactions of 3-Dimethylamino-2,2-dimethyl-2H-azirine with NH-Acidic Heterocycles; Synthesis of 4H-Imidazoles In this paper, reactions of 3-dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) with heterocyclic compounds containing the structure unit CO? NH? CO? NH are described. 5,5-Diethylbarbituric acid ( 5 ) reacts with 1 in refluxing 2-propanol to give the 4H-imidazole derivative 6 (Scheme 2) in 80% yield. The structure of 6 has been established by X-ray crystallography. Under similar conditions 1 and isopropyl uracil-6-carboxylate ( 7 ) yield the 4H-imidazole 8 (Scheme 3), the structure of which is deduced from spectral data and the degradation reactions shown in Scheme 3. Hydrolysis of 8 with 3N HCl at room temperature leads to the α-ketoester derivative 9 , which in refluxing methanol gives dimethyl oxalate and 5-dimethyl-amino-2,4,4-trimethyl-4H-imidazole ( 10 ). On hydrolysis the latter is converted to the known 2,4,4-trimethyl-2-imidazolin-5-one ( 11 ) [6]. Quinazolin-2,4 (1H, 3H)-dione ( 12 ) and imidazolidinetrione (parabanic acid, 14 ) undergo with 1 a similar reaction to give the 4H-imidazoles 13 and 15 , respectively (Schemes 4 and 5). In Scheme 6 two possible mechanisms for the formation of 4H-imidazoles from 1 and heterocycles of type 16 are formulated. The zwitterionic intermediate f corresponds to b in Scheme 1. Instead of dehydration as in the case of the reaction of 1 with phthalohydrazide [3], or ring expansion as with saccharin and cyclic imides [1] [2], f , undergoes ring opening (way A or B). Decarboxylation then leads to the 4H-imidazoles 17 .     

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).     

Reaktionen der valenzpolaromeren Ketenform mesoionischer Heterocyclen mit 3-Dimethylamino-2H-azirinen

Reactions of valencepolaromeric ketenes of mesoionic heterocyles with 3-dimethylamino-2H-azirines Reactions of the 3-dimethylamino-2H-azirines 1a and 1b with the mesoionic oxazole 5 and the mesoionic dithiole 6 in acetonitrile at room temperature yield the 1:1 adducts 11 , 12 , 19 and 20 , respectively (Schemes 5 and 8). These products can be formulated as adducts of the aminoazirines and the ketenes 5a and 6a , which are valence polaromeric forms of the mesoionic heterocycles 5 and 6 (Scheme 2). The structure of the adducts has been elucidated by spectral data and their comparison with the data of (Z)- 11 , the structure of which has been established by X-ray [19]. Oxidation of the 1:1 adducts with KMnO₄ in a two-phase system yields 4-dimethylamino-3-oxazolin-2-ones (cf. Scheme 6) by clevage of the exocyclic C,C-double bond. A mechanism for the formation of the adducts is given in Scheme 9: Nucleophilic attack of 1 on the ketene leads to a primary adduct of type a , which undergoes clevage of the former N(1), C(2)-azirine bond to give adducts of type 11 or 19 . The N(1), C(2)-ring opening of 1a in the reaction with ketenes contrasts with the N(1), C(3)-opening of 1a in the addition with, for instance, isothiocyanates. These different ring openings are explained by the difference in nucleophilicity of the heteroatoms X and Y in a ′ (Scheme 10).     

Synthese von 3,3-Dimethylperhydro-1,4-diazepin-2,5,7-trionen aus 3-Dimethylamino-2,2-dimethyl-2H-azirin und Malonsäuremonoamiden

Synthesis of 3,3-Dimethylperhydro-1,4-diazepin-2,5,7-triones from 3-Dimethylamino-2,2-dimethyl-2H-azirine and Malonic Acid Monoamides Reaction of the aminoazirine 1 and malonic acid monoamides 5 in CH₃CN yielded triamides of type 6 (Scheme 2), which were transformed to the corresponding phenylthioates 9 by treatment of a solution of 6 and thiophenol in CH₃CN with HCl (Scheme 4). Cyclization of 9 to give the 1,4-diazepin-2,5,7-trione of type 10 was achieved with NaH in toluene at about 90°. It has been shown that 2-oxazolin-5-ones are intermediates in the selective cleavage of the therminal amide function of 6 (Scheme 3).