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).     

Ring-Transformationen bei der Umsetzung von 3-(Dimethylamino)-2,2-dimethyl-2H-azirin mit 1-substituierten Imidazolidin-2,4,5-trionen

Ring-Transformations in the Reaction of 3-(Dimethylamino)-2,2-dimethyl-2H-azirines with 1-Substituted Imidazolidine-2,4,5-triones Reaction of 1-substituted imidazolidine-2,4,5-triones ( = N-substituted parabanic acids; 2 ) and 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) in i-PrOH or MeCN at room temperature yields 5,6,7,7a-tetrahydro-3H-imidazo[3,4-a]imidazole-5,7-diones 3 (Scheme 1). By ¹⁵N-NMR studies, using (3-¹⁵N)- 2a , it has been shown that only N( 1 ) in (¹⁵N)- 3a is labelled and, hence, N(4) stems from 1 , e.g. the azirine reacts via cleavage of the N(1)=C(3) bond. In MeCN at room temperature, the azacyclols 3 rearrange slowly to give monocyclic 2H, 5H-imidazol-2-ones 4 (Scheme 3); the ¹⁵N-label in (¹⁵N)- 4a is in position 1. Both reactions proceed via deep-seated skeletal rearrangements, most probably via ring-expansion/ring-contraction processes.     

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).     

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).     

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).     

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.     

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.     

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).     

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.     

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.     

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. 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 .     

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).     

Umsetzungen von 3-(Dimethylamino)-2,2-dimethyl-2H-azirin mit Barbitursäure-Derivaten

Reactions of 3-(Dimethylamino)-2,2-dimethyl-2H-azirines with Barbituric-Acid Derivatives The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) and 5,5-disubstituted barbituric acids 5 in i-PrOH at ca. 70° gives 2-[5-(dimethylamino)-4,4-dimethyl-4H-imidazol-2-yl]alkanamides of type 6 in good yields (Scheme 1). The formation of 6 proceeds with loss of CO₂; various reaction mechanisms with a zwitterionic 1:1 adduct B as common intermediate are discussed (Schemes 2 and 5). Thermolysis of product 6 leads to 2-alkyl-5-(dimethylamino)-4,4-dimethyl-4H-imidazoles 8 or the tautomeric 2-alkylidene derivatives 8 ′ via elimination of HNCO (Scheme 3). The latter undergoes trimerization to give 1,3,5-triazine-2,4,6-trione. No reaction is observed with 1,5,5-trisubstituted barbiturates and 1 in refluxing i-PrOH, but an N-alkylation of the barbiturate occurs in the presence of morpholine (Scheme 4). This astonishing reaction is explained by a mechanism via formation of the 2-alkoxy-2-(dimethylamino )aziridinium ion H which undergoes ring opening to give the O-alkylated 2-amino-N¹,N¹-dimethylisobutyramide I as alkylating reagent (Scheme 4).     

Herstellung und Reaktionen der valenzpolaromeren Verbindung (4,4-Dimethyl-2-thiazolin-5-dimethyliminium)-2-thiolat ⇌ (1-Dimethylthiocarbamoyl-1-methyl-äthyl)-isothiocyanat aus 3-Dimethyl-amino-2,2-dimethyl-2H-azirin und Schwefelkohlenstoff

Synthesis and reactions of the valence polaromeric compound (4,4-dimethyl-2-thiazoline-5-dimethyliminium)-2-thiolate ? 1-dimethylthiocarbamoyl-1-methyl-ethyl isothiocyanate from 3-dimethylamino-2,2-dimethyl-2H-azirine and carbon disulfide. 3-Dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) reacts with carbon disulfide to give crystals which have the dipolar structure 3a [(4,4-dimethyl-2-thiazoline-5-dimethyliminium)-2-thiolate, Scheme 1]. In solution, the non-dipolar (charge-free) isomeric form 3b (1-Dimethyl-thiocarbamoyl-1-methyl-ethyl isothiocyanate) is almost exclusively populated. Reaction products are derived from both forms: Derivatives of 3a are the hydrolysis product 6 , the sodium borohydride reduction product 7 and the methylation products 9 and 10 , respectively (Scheme 2). The isothiocyanate form 3b is responsible for the various reaction products with amines (Scheme 3). One of the reaction products with ammonia, namely 20 , is also obtained by the reaction of 1 with thiocyanic acid. Thermolysis of the azirine/carbon disulfide adduct 3 leads to 2-dimethylamino-4,4-dimethyl-2-thiazoline-5-thione ( 17 ) in high yield. A possible mechanism is outlined in Scheme 4. The same compound is also formed by rearrangement of 3 under the catalytic influence of dimethylamine. Its structure has been established by X-ray crystallography (section 4). Again a rearrangement is involved in the reductive (NaBH₄) conversion of 17 to 7 , the direct reduction product of the dipolar species 3a (Scheme 5). The isothiocyanate form 3b is able to react with a second molecule of 3-dimethylamino-2,2-dimethyl-2H-azirine ( 1 ) to yield compound 25 , which in the crystalline or dissolved state appears to be almost entirely populated by the carbodiimide form with structure 25b (Scheme 7), though all reaction products of 25 (reduction with sodium borohydride, addition of water or hydrogen sulfide, Schemes 7 and 8) are derived from the dipolar form 25a , not detectable as such; here again therefore there is a dynamic equilibrium 25a ? 25b . The two forms of adduct 3 , namely 3a and 3b , are obviously very easily interconverted at room temperature and therefore can be considered as valence polaromeric forms (section 5). A classification of the dipolar (zwitterionic) form is given, which allows a comparison of various dipolar species and gives as indication of charge stabilization by delocalization. The versatile reactivity of the 3-dimethylamino-2,2-dimethyl-2H-azirine/carbon disulfide adduct is demonstrated by the fact that with simple reagents approximately 25 derivatives have been obtained, most of them being new heterocyclic compounds.     

Reactions of 3,5-dibromo-1-(thiiran-2-ylmethyl)-1,2,4-triazole with NH-azoles

Reactions of 3,5-dibromo-1-(thiiran-2-ylmethyl)-1,2,4-triazole with 3,5-dimethylpyrazole, 1,3-dimethyl-3,7-dihydropurine-2,6-dione, 3,5-dibromo-1,2,4-triazole, 2,4,5-tribromoimidazole, and 2-chlorobenzimidazole lead to the formation of 5-azolylmethyl-2-bromo-5,6-dihydrothiazolo[3,2-b]-1,2,4-triazoles. In the case of 8-bromo-1,3-dimethyl-3,7-dihydropurine-2,6-dione the intermediate thiolate anion undergoes cyclization into 7-[(3,5-dibromo-1,2,4-triazol-1-yl)methyl]-1,3-dimethyl-6,7-dihydrothiazolo[2,3-f]purine-2,4(1H,3H)-dione. The structure of reaction products depends on the relative rate of substitution of leaving groups in the reagents.     

Reactions of 1,2,4-triazole derivatives with a “model” thiirane

Reactions of 3-mono- and 3,5-disubstituted 1,2,4-triazoles with a “model” thiirane, 8-bromo-1,3-dimethyl-7-(thiiran-2-ylmethyl)-3,7-dihydro-1H-purine-2,6-diones proceed at the positions N¹ and N² of the triazole ring and yield 7-(5-R-3-R′-1,2,4-triazol-1-yl)methyl- and/or 7-(5-R′-3-R-1,2,4-triazol-1-yl)methyl-1,3-dimethyl-6,7-dihydro[1,3]thiazolo[2,3-f]-purine-2,4-(1H,3H)-diones. 3-Methylsulfonyl-1,2,4-triazole reacted regiospecifically at the position N¹ forming 1,3-dimethyl-7-[(3-methyl-sulfonyl-1,2,4-triazole-1-yl)-methyl]-6,7-dihydro[1,3]thiazolo-[2,3-f]purine-2,4(1H,3H)-dione.     

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).     

Ringerweiterung von sechs- zu neungliedrigen Heterocyclen: Umsetzung von 3-(Dimethylamino)-2,2-dimethyl-2H-azirin mit 3,4-Dihydro-2H-1,2,4-benzothiadiazin-3-on-1,1-dioxiden

Ring Enlargement of Six- to Nine-Membered Heterocycles: Reaction of 3-(Dimethylamino)-2,2-dimethyl-2H-azirine with 3,4-Dihydro-2H-1,2,4-benzothiadiazin-3-one 1,1-Dioxides Reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine ( 1 ) and N-substituted 3,4-dihydro-2H-1,2,4-benzothiadiazin-3-one 1,1-dioxides ( 4 ) in CHCl₃ yields 3-(dimethylamino)-4,5,6,7-tetrahydro-1,2,5,7-benzothiatriazonin-6-one 1,1-dioxides 5 , a novel nine-membered heterocyclic system, by ring enlargement (Schemes 2 and 4). In refluxing MeOH, the heterocycle 5a rearranges to give the N-[1-methyl-1-(1,1-dioxo-4H-1,2,4-benzothiadiazin-3-yl)ethyl]-N′, N′-dimethylurea 10 . The three isomeric 2-(methylamino)benzenesufonamides 8,9 , and 11 (Scheme 3) are obtained by naBH₄ reduction of 5a and 10 , respectively. Mechanisms for the thermal isomerization 5a → 10 and the NaBH₄ reduction of 5a are proposed in Schemes 5 and 6.