Pteridines. Part CXVII

A series of side chain reactions starting from the 6‐ and 7‐styryl‐substituted 1,3‐dimethyllumazines 1 and 21 as well as from the 6‐ and 7‐[2‐(methoxycarbonyl)ethenyl]‐substituted 1,3‐dimethyllumazine 2 and 22 were performed first by addition of Br₂ to the C?C bond forming the 1′,2′‐dibromo derivatives 3, 4, 24 , and 26 in high yields (Schemes 1 and 3) (lumazine=pteridine‐2,4(1H,3H)‐dione). Treatment of 3 with various nucleophiles gave rise to an unexpected tele‐substitution in 7‐position and elimination of the Br‐atoms generating 7‐alkoxy‐ (see 5 and 6 ), 7‐hydroxy‐ (see 7 ) and 7‐amino‐6‐styryl‐1,3‐dimethyllumazines (see 8 – 11 ) (Scheme 1). On the other hand, 4 underwent, with dilute DBU (1,8‐diazabicyclo[5.4.0]undec‐2‐ene), a normal HBr elimination in the side chain leading to 18 , whereas treatment with MeONa afforded a more severe structural change to 19 . Similarly, 24 and 26 reacted to 27, 32 , and 33 under mild conditions, whereas in boiling NaOMe/MeOH, 24 gave 7‐(2‐dimethoxy‐2‐phenylethyl)‐1,3‐dimethyllumazine ( 30 ) which was hydrolyzed to give 31 (Scheme 3). From the reactions of 4 and 24 with DBU resulted the dark violet substance 20 and 25 , respectively, in which DBU was added to the side chain (Scheme 2). The styryl derivatives 1 and 21 could be converted, by a Sharpless dihydroxylation reaction, into the corresponding stereoisomeric 6‐ and 7‐(1,2‐dihydroxy‐2‐phenylethyl)‐1,3‐dimethyllumazines 34 – 37 (Scheme 4). The dihydroxy compounds 34 and 35 were also acetylated to 38 and 39 which, on catalytic reduction followed by formylation, yielded the diastereoisomer mixtures 40 and 41 . Deacetylation to 42 and 45 allowed the chromatographic separation of the diastereoisomers resulting in the isolation of 43 and 44 as well as 46 and 47 , respectively. Introduction of a 6‐ or 7‐ethynyl side chains proceeded well by a Sonogashira reaction with 6‐ ( 48 ) or 7‐chloro‐1,3‐dimethyllumazine ( 55 ) yielding 49 – 51 and 56 – 58 (Scheme 5). The direction of H₂O addition to the triple bond is depending on the substituents since the 6‐ ( 49 ) and 7‐(phenylethynyl)‐1,3‐dimethyllumazine ( 56 ) showed attack at the 2′‐position yielding 53 and 60 , in contrast to the 6‐ ( 51 ) and 7‐ethynyl‐1,3‐dimethyllumazine ( 58 ) favoring attack at C(1′) and formation of 6‐ ( 52 ) and 7‐acetyl‐1,3‐dimethyllumazine ( 59 ).     

2,3‐Diaryl‐3‐hydroxy­propionic acid inter­mediates in the synthesis of threo forms of 1,2‐diaryl‐1,3‐propane­diols

Racemic threo‐3‐hydroxy‐2,3‐diphenyl­propionic acid, C₁₅H₁₄O₃, (I), crystallizes from ethyl acetate as a conglomerate of separate (+)‐ and (−)‐crystals. The geometries of (I) and its methyl ester are compared. Reduction of (I) gives threo‐1,2‐diphenyl‐1,3‐propane­diol. The synthesis of threo forms of 1,2‐diaryl‐1,3‐propane­diols via 2,3‐diaryl‐3‐hydroxy­propionic acids is discussed.     

Chemie freier cyclischer vicinaler Tricarbonyl‐Verbindungen (‘1,2,3‐Trione’). Teil 3

Chemistry of Free Cyclic Vicinal Tricarbonyl Compounds (‘1,2,3‐Triones’). Part 3. Polar and Redox Reactions of 1,2,3‐Triones with Enamines of Different Types – News on Oxonol Dyes, Radicals, and Biradicals The central C?O groups of cyclic 1,2,3‐triones possess outstanding electrophilic (electron‐pair‐accepting) as well as oxidizing (one‐electron‐accepting) properties. Thus, 1,2,3‐triones are chemically related to 1,2‐ and 1,4‐benzoquinones. Whereas polar reactions with carbanion‐like (electron rich) species give rise to nucleophilic addition reactions to C?O groups under exclusive C,C‐bond formation, SET (single‐electron transfer) or redox reactions effect a partial ‘carbonyl Umpolung’ via ketyl intermediates (C,C‐ and/or C,O‐bond formation). Here, we report on numerous reactions between electron‐rich, more‐ or less‐polar enamines with 5,5‐dimethylcyclohexane‐1,2,3‐trione ( 9a ) and 1H‐indene‐1,2,3‐trione ( 9b ). Various new derivatives of basic oxonol dyes were formed, including the first oxonol dye incorporating a 1,3‐dioxocyclohexyl moiety. A novel stable radical, 50 / 50′ , was obtained from 9b and 11a via addition, hydrolysis, and treatment with conc. H₂SO₄. Radical 50 / 50′ represents a vinylogous ‘monodehydroreductone’ and is, thus, related to monodehydroascorbic acid ( 143 ), to Russell's radical cation ( 144 ), to indigo ( 141 / 141′ ), and to quinhydrone.     

Synthesis of Phospholipid?Ribavirin Conjugates

New conjugates of antiviral nucleoside Ribavirin (=1‐(β‐D ‐ribofuranosyl)‐1H‐1,2,4‐triazole‐3‐carboxamide; 1 ) with 1,2‐ and 1,3‐diacyl glycerophosphates have been synthesized by the phosphoramidite method. A combination of 2′,3′‐phenylboronate protecting group for the sugar moiety of the ribonucleoside 1 and 2‐cyanoethyl protection for the phosphate fragment ensured the preparation of the desired compounds with reasonable yields via a small number of synthetic steps.     

Ozonolyse von Enolethern, 8. Mitteilung

Ozonolysis of Enol Ethers. Part 8. Ozonation of (1‐Methoxy‐2‐methylprop‐1‐enyl)‐1,1′‐biphenyl in Comparison with Related Oxygenations The results of conversions of 4‐(1‐methoxy‐2‐methylprop‐1‐enyl)‐1,1′‐biphenyl ( 19 ) with ozone and with dimethyldioxirane ( 6b ) under ‘normal' and ‘inverse' conditions are compared with oxygenations by dioxygen under thermal and sensitized photochemical conditions, as well as with the photooxygenation of epoxide 17 , formally derived from 19 . Ozone consumption varies between 0.7 and 1 mol‐equiv. amounts, peroxidic species are not formed. Except for bicyclus 24 , all conversions lead to mixtures of the same [1,1′‐biphenyl]‐4‐yl compounds which only differ by varying percentages. It is concluded that ozonolysis of CC bonds only represents a special type of electron‐transfer oxygenation.     

Synthese und Reaktivität von 2‐Brom‐1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol Molekülstruktur von Bis(1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol‐2‐yl)

Synthesis and Reactivity of 2‐Bromo‐1,3‐diethyl‐2,3‐dihydro‐1 H ‐1,3,2‐benzodiazaborole Molecular Structure of Bis(1,3‐diethyl‐2,3‐dihydro‐1 H ‐1,3,2‐benzodiazaborol‐2‐yl The reaction of a slurry of calcium hydride in toluene with N,N′‐diethyl‐o‐phenylenediamine ( 1 ) and boron tribromide affords 2‐bromo‐1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol ( 2 ) as a colorless oil. Compound 2 is converted into 2‐cyano‐1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborole ( 3 ) by treatment with silver cyanide in acetonitrile. Reaction of 2 with an equimolar amount of methyllithium affords 1,3‐diethyl‐2‐methyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborole ( 4 ). 1,3,2‐Benzodiazaborole is smoothly reduced by a potassium‐sodium alloy to yield bis(1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol‐2‐yl] ( 7 ), which crystallizes from n‐pentane as colorless needles. Compound 7 is also obtained from the reaction of 2 and LiSnMe₃ instead of the expected 2‐trimethylstannyl‐1,3,2‐benzodiazaborole. N,N′‐Bis(1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol‐2‐ yl)‐1,2‐diamino‐ethane ( 6 ) results from the reaction of 2 with Li(en)C≡CH as the only boron containing product. Compounds 2 – 4 , 6 and 7 are characterized by means of elemental analyses and spectroscopy (IR, ¹H‐, ¹¹B{¹H}‐, ¹³C{¹H}‐NMR, MS). The molecular structure of 7 was elucidated by X‐ray diffraction analysis.     

Stereochemistry of the Conversion of 2‐Phenoxyethanol into Phenol and Acetaldehyde by Acetobacterium sp.

The conversion of 2‐phenoxyethanol to phenol and acetate by the anaerobic bacterium Acetobacterium sp. strain LuPhet1 proceeds through acetaldehyde with concomitant migration of a H‐atom from C(1) to C(2) of the glycolic moiety. Separate feeding experiments with (R)‐ and (S)‐2‐phenoxy(1‐²H)ethanol, prepared via chemoenzymatic syntheses, indicate that the H‐atom involved in the 1,2‐shift is the pro‐S one of the enantiotopic couple of the alcohol function.     

Studies on the Flash Vacuum Thermolysis of Thiones of Selected N‐, O‐, and S‐Heterocycles

Thermal decomposition of thiones of selected N‐, O‐ and S‐heterocycles under flash vacuum thermolysis conditions was investigated. In the case of six‐membered 4H‐3,1‐benzoxathiin‐4‐thione 6 , the course of the reaction depended on the substitution pattern at C(2) (Scheme 3). Thus, the 2‐unsubstituted derivative 6a led to the unstable product 2 , which upon treatment with MeOH was converted quantitatively into methyl 2‐mercaptobenzoate ( 7 ). The analogous thermolysis of the 2,2‐dimethyl derivative 6b yielded 2‐methyl‐4H‐1‐benzothiopyran‐4‐thione ( 8 ) as a sole product. In the case of thiophthalide derivatives 15 , a thermal rearrangement in the gas phase leading to the corresponding benzo[c]thiophen‐1(3H)‐ones 16 in high yields was observed (Scheme 6). Unexpectedly, thionation of 1,3‐oxathiolan‐5‐one 17 with Lawesson's reagent under standard conditions led to 1,2‐dithietane derivative 19 , which, after the gas‐phase thermolysis, underwent a ring enlargement to yield 3H‐1,2‐dithiole 20 (Scheme 7). The six‐membered 4H‐1,3‐benzothiazine‐4‐thione 21 was shown to give three products: phenanthro[9,10‐c]‐1,2‐dithiete ( 22 ), 3H‐1,3‐benzodithiole‐3‐thione ( 23 ), and N‐(3H‐1,2‐benzodithiol‐3‐ylidene)prop‐2‐en‐1‐amine ( 24 ) (Scheme 8). The latter is the product of the initial reaction, whereas 22 and 23 are postulated to be formed as secondary products of the conversion of the intermediate 6‐(thioxomethylene)cyclohexa‐2,4‐diene‐1‐thione ( 26 ) (Schemes 9 and 10).     

Behavior of 3(2‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones and 3(3‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones as alkylating agents: A comparative study

3(2‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones and 3(3‐pyridinylmethylene)‐5‐aryl‐2(3H)‐furanones were prepared as a mixture of (E) and (Z) stereoisomers by condensing pyridine‐2‐carboxaldehyde and pyridine‐3‐carboxaldehyde with 3‐aroylpropionic acids. The reaction of the furanones 6 and 7 with anhydrous aluminium chloride in benzene led to the formation of 4,4‐diaryl‐1‐(2‐pyridinyl)but‐1,3‐diene ( 8 ) and 4,4‐diaryl‐1‐(3‐pyridinyl)but‐1,3‐diene ( 9 ) as mixtures of geometrical (E,E‐ and E,Z‐) stereoisomers via an intermolecular alkylation mode. When the reaction was carried out in tetrachloroethane as a solvent, the reaction of 6 gave 5‐arylquinoline‐7‐carboxylic acid via intramolecular alkylation mode. This may be considered as a novel method for the synthesis of quinoline derivatives. J. Heterocyclic Chem., (2011).     

Azinoiminophosphorane mediated 4H,8H‐1,2,4‐triazolo[1,5‐C]‐[1,3]oxazepin‐4‐ones and 5,6‐dihydro‐7H, 12H‐naphtho[2,1‐f]‐[1,2,4]triazolo[1,5‐c][1,3]oxazepin‐7‐ones synthesis

The aza‐Wittig reactions of benzaldehyde‐, acetophenone‐ and benzophenone 1‐[(triphenylphosphor‐anylidene)amino]ethylidenehydrazones ( 1 ) with 2,3‐furandiones 6 provide a new route to 4H,8H‐1,2,4‐triazolo[1,5‐c][1,3]oxazepin‐4‐ones 14 or 5,6‐dihydro‐7H,12H‐naphtho[2,1‐f|[1,2,4]triazolo[1,5‐c]‐[1,3]oxazepin‐7‐ones 17 via the thermal reaction of the expected azinoimine vinylogous lactones.     

Reduction of Thiocarbonyl Compounds with Lithium Diisopropylamide

Treatment of 4,4‐disubstituted 2‐phenyl‐1,3‐thiazole‐5(4H)‐thiones with lithium diisopropylamide (LDA; LiNⁱPr₂) in THF at ?78° yielded the corresponding 1,3‐thiazole‐5(4H)‐thioles in moderate yields. Sequential treatment with LDA and MeI under the same conditions led to the 5‐methylsulfanyl derivatives. Similarly, reaction of some cycloalkanethiones as well as diaryl thioketones with LDA and MeI gave cycloalkyl methyl sulfides and diarylmethyl methyl sulfides, respectively. A reaction mechanism via H transfer from LDA to the thiocarbonyl C‐atom via a six‐membered transition state is proposed for this unprecedented reduction of the C?S bond.     

Azinoiminophosphorane mediated synthesis of 5H, 7H‐1,2,4‐triazolo[1,5‐c][1,3]benzoxazepin‐7‐ones and 6H,8H‐1,2,4‐triazolo‐[1,5‐c][1,3]oxazepin‐6‐ones

The aza‐Wittig reactions of benzophenone‐, acetophenone‐ and benzaldehyde l‐[(triphenylphosphoranyl‐idene)amino]ethylidenehydrazones (4) with phthalic anhydride, 2,3‐dimethylmaleic anhydride and 7‐oxabi‐cyclo[2,2,l]hept‐5‐ene‐2,3‐dicarboxylic anhydride ( 5a ) provide a new route to 5H,7H‐1,2,4‐triazolo[1,5‐c]‐[1,3]benzoxazepin‐7‐ones 8a‐c or 6H,8H‐1,2,4‐triazolo[1,5‐c][1,3]oxazepin‐6‐ones 8d‐h via the thermal reaction of the expected azinoimine lactones 6 .     

A new insight into the mechanism of 1,3‐dienes cationic polymerization. II. Structure of poly(1,3‐pentadiene) synthesized with tBuCl/TiCl4 initiating system

The microstructure of poly(1,3‐pentadiene) synthesized by cationic polymerization of 1,3‐pentadiene with ^tBuCl/TiCl₄ initiating system is analyzed using one‐dimensional‐ and two‐dimensional‐NMR spectroscopy. It is shown that unsaturated part of chain contains only homo and mixed dyads with trans?1,4‐, trans?1,2‐, and cis?1,2‐structures with regular and inverse (head‐to‐head or tail‐to‐tail) enchainment, whereas cis?1,4‐ and 3,4‐units are totally absent. The new quantitative method for the calculation of content of different structural units in poly(1,3‐pentadiene)s based on the comparison of methyl region of ¹³C NMR spectra of original and hydrogenated polymer is proposed. The signals of tert‐butyl head and chloromethyl end groups are identified in a structure of poly(1,3‐pentadiene) chain and the new approaches for the quantitative calculation of number‐average functionality at the α‐ and ω‐end are proposed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3297–3307     

An Efficient Synthesis of Spiro‐oxindole Derivatives by Three‐Component Reactions in Water

An efficient synthesis of (3S)‐1,1′,2,2′,3′,4′,6′,7′‐octahydro‐9′‐nitro‐2,6′‐dioxospiro[3H‐indole‐3,8′‐[8H]pyrido[1,2‐a]pyrimidine]‐7′‐carbonitrile is achieved via a three‐component reaction of isatin, ethyl cyanoacetate, and 1,2,3,4,5,6‐hexahydro‐2‐(nitromethylidene)pyrimidine. The present method does not involve any hazardous organic solvents or catalysts. Also the synthesis of ethyl 6′‐amino‐1,1′,2,2′,3′,4′‐hexahydro‐9′‐nitro‐2‐oxospiro[3H‐indole‐3,8′‐[8H]pyrido[1,2‐a]pyrimidine]‐7′‐carboxylates in high yields, at reflux, using a catalytic amount of piperidine, is described. The structures were confirmed spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS data) and by elemental analyses. A plausible mechanism for this reaction is proposed (Scheme 2).     

Poly[[tetraaquabis(μ2‐2‐nitroterephthalato‐κ3O1:O4,O4′)(μ2‐piperazine‐κ3N:N′)dicadmium(II)] dihydrate]

In the title complex, {[Cd₂(C₈H₃NO₆)₂(C₄H₁₀N₂)(H₂O)₄]·2H₂O}_n, the Cd^II atoms show distorted octahedral coordination. The two carboxylate groups of the dianionic 2‐nitroterephthalate ligand adopt monodentate and 1,2‐bridging modes. The piperazine molecule is in a chair conformation and lies on a crystallographic inversion centre. The Cd^II atoms are connected via three O atoms from two carboxylate groups and two N atoms from piperazine molecules to form a two‐dimensional macro‐ring layer structure. These layers are further aggregated to form a three‐dimensional structure via rich intra‐ and interlayer hydrogen‐bonding networks. This study illustrates that, by using the labile Cd^II salt and a combination of 2‐nitroterephthalate and piperazine as ligands, it is possible to generate interesting metal–organic frameworks with rich intra‐ and interlayer O—H...O hydrogen‐bonding networks.     

Reaction of Optically Active Oxiranes with Thiofenchone and 1‐Methylpyrrolidine‐2‐thione: Formation of 1,3‐Oxathiolanes and Thiiranes

The SnCl₄‐catalyzed reaction of (?)‐thiofenchone (=1,3,3‐trimethylbicyclo[2.2.1]heptane‐2‐thione; 10 ) with (R)‐2‐phenyloxirane ((R)‐ 11 ) in anhydrous CH₂Cl₂ at ?60° led to two spirocyclic, stereoisomeric 4‐phenyl‐1,3‐oxathiolanes 12 and 13 via a regioselective ring enlargement, in accordance with previously reported reactions of oxiranes with thioketones (Scheme 3). The structure and configuration of the major isomer 12 were determined by X‐ray crystallography. On the other hand, the reaction of 1‐methylpyrrolidine‐2‐thione ( 14a ) with (R)‐ 11 yielded stereoselectively (S)‐2‐phenylthiirane ((S)‐ 15 ) in 56% yield and 87–93% ee, together with 1‐methylpyrrolidin‐2‐one ( 14b ). This transformation occurs via an S_N2‐type attack of the S‐atom at C(2) of the aryl‐substituted oxirane and, therefore, with inversion of the configuration (Scheme 4). The analogous reaction of 14a with (R)‐2‐{[(triphenylmethyl)oxy]methyl}oxirane ((R)‐ 16b ) led to the corresponding (R)‐configured thiirane (R)‐ 17b (Scheme 5); its structure and configuration were also determined by X‐ray crystallography. A mechanism via initial ring opening by attack at C(3) of the alkyl‐substituted oxirane, with retention of the configuration, and subsequent decomposition of the formed 1,3‐oxathiolane with inversion of the configuration is proposed (Scheme 5).     

Massive Steric Hindrance in Two ‘Thiocarbonyl Ylides': Cycloadditions with Tetra‐Acceptor‐Substituted Ethylenes via Zwitterionic Intermediates

The switch from a concerted to a two‐step pathway of 1,3‐dipolar cycloadditions was recently established for the reactions of sterically hindered ‘thiocarbonyl ylides' with acceptor ethylenes. This mechanism via zwitterionic intermediates is studied here for 1,3‐dipoles 5A and 5B , which are derived from 2,2,5,5‐tetramethylcyclopentanethione and 1,1,3,3‐tetramethylindan‐2‐thione, respectively, and contain a highly screened reaction center. In the reactions of 8A and 8B (the precursors of 5A and 5B ) with dimethyl 2,3‐dicyanofumarate ( 15 ) and 2,3‐dicyanomaleate ( 16 ), virtually identical ratios of cis‐ and trans‐thiolanes were observed ( 17 / 18 93 : 7 for 5a and 94 : 6 for 5B ). Thus, full equilibration of rotameric zwitterions precedes cyclization; an anteceding disturbing isomerization 15 ⇌ 16 had to be circumvented. The cis,trans assignment of the cycloadducts rests on three X‐ray analyses. The kinetically favored cis‐thiolanes 17 isomerize at >80° to 18 (trans), and irreversible cleavage leads to thione 7 and trans,cis isomeric dimethyl 1,2‐dicyanocyclopropane‐1,2‐dicarboxylates ( 27 and 28 , resp.). Furthermore, the zwitterionic intermediates equilibrate with the cyclic seven‐membered ketene imine 21 , which was intercepted under conditions where the solvent contained 2 vol‐% of H₂O or MeOH. Lactams 22 were obtained with H₂O in high yields, and the primary products of capturing by MeOH were the cyclic ketene O,N‐acetals 23 , which subsequently tautomerized to the lactim methyl ethers 24 . When 5B was reacted with ethenetetracarbonitrile in CDCl₃/MeOH (98 : 2 vol‐%), the analogous cyclic ketene imine 13B was trapped to the extent of 93%.     

Synthesis of Macrocyclic Lactones via Ring Transformation of 4‐(ω‐Hydroxyalkyl)‐1,3‐oxazol‐5(4H)‐ones

The synthesis of α‐benzamido‐α‐benzyl lactones 23 of various ring size was achieved either via ‘direct amide cyclization’ by treatment of 2‐benzamido‐2‐benzyl‐ω‐hydroxy‐N,N‐dimethylalkanamides 21 in toluene at 90 – 110° with HCl gas or by ‘ring transformation’ of 4‐benzyl‐4‐(ω‐hydroxyalkyl)‐2‐phenyl‐1,3‐oxazol‐5(4H)‐ones under the same conditions. The precursors were obtained by C‐alkylations of 4‐benzyl‐2‐phenyl‐1,3‐oxazol‐5(4H)‐one ( 15 ) with THP‐ or TBDMS‐protected ω‐hydroxyalkyl iodides. Ring opening of the THP‐protected oxazolones by treatment with Me₂NH followed by deprotection of the OH group gave the diamides 21 , whereas deprotection of the TBDMS series of oxazolones 25 with TBAF followed by treatment with HCl gas led to the corresponding lactones 23 in a one‐pot reaction.     

1,3‐Bis(ethylamino)‐2‐nitrobenzene, 1,3‐bis(n‐octylamino)‐2‐nitrobenzene and 4‐ethylamino‐2‐methyl‐1H‐benzimidazole

1,3‐Bis(ethylamino)‐2‐nitrobenzene, C₁₀H₁₅N₃O₂, (I), and 1,3‐bis(n‐octylamino)‐2‐nitrobenzene, C₂₂H₃₉N₃O₂, (II), are the first structurally characterized 1,3‐bis(n‐alkylamino)‐2‐nitrobenzenes. Both molecules are bisected though the nitro N atom and the 2‐C and 5‐C atoms of the ring by twofold rotation axes. Both display intramolecular N—H...O hydrogen bonds between the amine and nitro groups, but no intermolecular hydrogen bonding. The nearly planar molecules pack into flat layers ca 3.4 Å apart that interact by hydrophobic interactions involving the n‐alkyl groups rather than by π–π interactions between the rings. The intra‐ and intermolecular interactions in these molecules are of interest in understanding the physical properties of polymers made from them. Upon heating in the presence of anhydrous potassium carbonate in dimethylacetamide, (I) and (II) cyclize with formal loss of hydrogen peroxide to form substituted benzimidazoles. Thus, 4‐ethylamino‐2‐methyl‐1H‐benzimidazole, C₁₀H₁₃N₃, (III), was obtained from (I) under these reaction conditions. Compound (III) contains two independent molecules with no imposed internal symmetry. The molecules are linked into chains via N—H...N hydrogen bonds involving the imidazole rings, while the ethylamino groups do not participate in any hydrogen bonding. This is the first reported structure of a benzimidazole derivative with 4‐amino and 2‐alkyl substituents.     

A Facile and Efficient Synthesis of Arylsulfonamido‐Substituted 1,5‐Benzodiazepines and N‐[2‐(3‐Benzoylthioureido)aryl]‐3‐oxobutanamide Derivatives

A facile and efficient synthesis of 1,5‐benzodiazepines with an arylsulfonamido substituent at C(3) is described. 1,5‐Benzodiazepine, derived from the condensation of benzene‐1,2‐diamine and diketene, reacts with an arylsulfonyl isocyanate via an enamine intermediate to produce the title compounds of potential synthetic and pharmacological interest in good yields (Scheme 1). In addition, reaction of benzene‐1,2‐diamine and diketene in the presence of benzoyl isothiocyanate leads to N‐[2‐(3‐benzoylthioureido)aryl]‐3‐oxobutanamide derivatives (Scheme 2). This reaction proceeds via an imine intermediate and ring opening of diazepine. The structures were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 3).