Strategy to Construct Stair‐Shaped Partially Reduced Naphtho[1,2‐b]pyrano[2,3‐d]oxepines and Dinaphtho[1,2‐b,d]oxepines

A concise and efficient base‐induced synthesis of stair‐shaped, 4‐methylthio‐2‐oxo‐5,6‐dihydro‐2H‐naphtho[1,2‐b]pyran[2,3‐d]oxepine‐3‐carbonitriles ( 3 ) has been delineated by the reaction of 3,4‐dihydronaphtho[1,2‐b]oxepin‐5(2H)‐one ( 1 ) and methyl 2‐cyano‐3,3‐dimethylthioacrylate in DMSO using powdered KOH as a base at room temperature. Amination of 3 has been achieved by reaction with secondary amine in ethanol at reflux temperature to yield 4‐sec‐amino‐2‐oxo‐5,6‐dihydro‐2H‐naphtho[1,2‐b]pyran[2,3‐d]oxepine‐3‐carbonitriles ( 4 ). Reaction of 3 with aryl methyl ketone ( 5 ) in DMSO at room temperature using powdered KOH as a base produced stair‐shaped 5‐aryl‐7,8‐dihydro‐1,4‐dioxa‐2,3‐dioxodinaphtho[1,2‐b,d]oxepine ( 6 ) in good yields. However, reaction of 6‐aryl‐2H‐pyran‐2‐one‐3‐carbonitrile ( 8 ) with 3,4‐dihydronaphtho[1,2‐b]oxepin‐5(2H)‐one ( 1 ) did not give similar product, but in lieu 4‐aryl‐5,6‐dihydronaphtho[1,2‐b]oxepino[4,5‐b]pyran‐2‐ylidene)acetonitrile ( 9 ) was isolated and characterized.     

Benzo[1,2‐b:4,5‐b′]dithiophene Building Block for the Synthesis of Semiconducting Polymers

This review covers the synthesis and polymerization of benzo[1,2‐b: 4,5‐b′]dithiophene (BDT) to generate semiconducting polymers used in organic field‐effect transistors (OFET) and organic solar cells applications.     

Synthesis and Structure–Property Relationships of 2,2′‐Bis(benzo[b]phosphole) and 2,2′‐Benzo[b]phosphole–Benzo[b]heterole Hybrid π Systems

The first comprehensive study of the synthesis and structure–property relationships of 2,2′‐bis(benzo[b]phosphole)s and 2,2′‐benzo[b]phosphole–benzo[b]heterole hybrid π systems is reported. 2‐Bromobenzo[b]phosphole P‐oxide underwent copper‐assisted homocoupling (Ullmann coupling) and palladium‐catalyzed cross‐coupling (Stille coupling) to give new classes of benzo[b]phosphole derivatives. The benzo[b]phosphole–benzo[b]thiophene and ‐indole derivatives were further converted to P,X‐bridged terphenylenes (X=S, N) by a palladium‐catalyzed oxidative cycloaddition reaction with 4‐octyne through the C_β? H activation. X‐ray analyses of three compounds showed that the benzo[b]phosphole‐benzo[b]heterole derivatives have coplanar π planes as a result of the effective conjugation through inter‐ring C? C bonds. The π–π* transition energies and redox potentials of the cis and trans isomers of bis(benzo[b]phosphole) P‐oxide are very close to each other, suggesting that their optical and electrochemical properties are little affected by the relative stereochemistry at the two phosphorus atoms. The optical properties of the benzo[b]phosphole–benzo[b]heterole hybrids are highly dependent on the benzo[b]heterole subunits. Steady‐state UV/Vis absorption/fluorescence spectroscopy, fluorescence lifetime measurements, and theoretical calculations of the non‐fused and acetylene‐fused benzo[b]phosphole–benzo[b]heterole π systems revealed that their emissive excited states consist of two different conformers in rapid equilibrium.     

An Efficient Synthesis of Benzo[g]thiazolo[2,3‐b]quinazolin‐4‐ium and Benzo[g]benzo[4,5]thiazolo[2,3‐b]quinazolin‐14‐ium Hydroxides by a One‐pot,Three‐component Reaction under Green Conditions

A new series of benzo[g]thiazolo[2,3‐b]quinazolin‐4‐ium and benzo[g]benzo[4,5]thiazolo[2,3‐b]quinazolin‐14‐ium hydroxide derivatives have been synthesized by the one‐pot, three‐component reaction of aryl glyoxal monohydrates, 2‐hydroxy‐1,4‐naphthoquinone, and 2‐aminothiazole or 2‐aminobenzothiazole in the presence of triethylamine and p‐toluenesulfonic acid as organocatalysts in H₂O/acetone (2:1) at room temperature. This method offers mild reaction conditions, excellent yields, easy workup, and readily accessible starting materials and catalysts.     

Benzo[a]heptalenes from Heptaleno[1,2‐c]furans. Part 2

It is shown in this ‘Part 2’ that heptaleno[1,2‐c]furans 1 react thermally in a Diels–Alder‐type [4+2] cycloaddition at the furan ring with vinylene carbonate (VC), phenylsulfonylallene (PSA), α‐(acetyloxy)acrylonitrile (AAN), and (1Z)‐1,2‐bis(phenylsulfonyl)ethene (ZSE) to yield the corresponding 1,4‐epoxybenzo[d]heptalenes (cf. Schemes 1, 5, 6, and 8). The thermal reaction of 1a and 1b with VC at 130° and 150°, respectively, leads mainly to the 2,3‐endo‐cyclocarbonates 2,3‐endo‐ 2a and ‐ 2b and in minor amounts to the 2,3‐exo‐cyclocarbonates 2,3‐exo‐ 2a and ‐ 2b . In some cases, the (P*)‐ and (M*)‐configured epimers were isolated and characterized (Scheme 1). Base‐catalyzed cleavage of 2,3‐endo‐ 2 gave the corresponding 2,3‐diols 3 , which were further transformed via reductive cleavage of their dimesylates 4 into the benzo[a]heptalenes 5a and 5b , respectively (Scheme 2). In another reaction sequence, the 2,3‐diols 3 were converted into their cyclic carbonothioates 6 , which on treatment with (EtO)₃P gave the deoxygenated 1,4‐dihydro‐1,4‐epoxybenzo[d]heptalenes 7 . These were rearranged by acid catalysis into the benzo[a]heptalen‐4‐ols 8a and 8b , respectively (Scheme 2). Cyclocarbonate 2,3‐endo‐ 2b reacted with lithium diisopropylamide (LDA) at ?70° under regioselective ring opening to the 3‐hydroxy‐substituted benzo[d]heptalen‐2‐yl carbamate 2,3‐endo‐ 9b (Scheme 3). The latter was O‐methylated to 2,3‐endo‐(P*)‐ 10b . The further way, to get finally the benzo[a]heptalene 13b with MeO groups in 1,2,3‐position, could not be realized due to the fact that we found no way to cleave the carbamate group of 2,3‐endo‐(P*)‐ 10b without touching its 1,4‐epoxy bridge (Scheme 3). The reaction of 1a with PSA in toluene at 120° was successful, in a way that we found regioisomeric as well as epimeric cycloadducts (Scheme 5). Unfortunately, the attempts to rearrange the products under strong‐base catalysis as it had been shown successfully with other furan–PSA adducts were unsuccessful (Scheme 4). The thermal cycloaddition reaction of 1a and 1b with AAN yielded again regioisomeric and epimeric adducts, which could easily be transformed into the corresponding 2‐ and 3‐oxo products (Scheme 6). Only the latter ones could be rearranged with Ac₂O/H₂SO₄ into the corresponding benzo[a]heptalene‐3,4‐diol diacetates 20a and 20b , respectively, or with trimethylsilyl trifluoromethanesulfonate (TfOSiMe₃/Et₃N), followed by treatment with NH₄Cl/H₂O, into the corresponding benzo[a]heptalen‐3,4‐diols 21a and 21b (Scheme 7). The thermal cycloaddition reaction of 1 with ZSE in toluene gave the cycloadducts 2,3‐exo‐ 22a and ‐ 22b as well as 2‐exo,3‐endo‐ 22c in high yields (Scheme 8). All three adducts eliminated, by treatment with base, benzenesulfinic acid and yielded the corresponding 3‐(phenylsulfonyl)‐1,4‐epoxybenzo[d]heptalenes 25 . The latter turned out to be excellent Michael acceptors for H₂O₂ in basic media (Scheme 9). The Michael adducts lost H₂O on treatment with Ac₂O in pyridine and gave the 3‐(phenylsulfonyl)benzo[d]heptalen‐2‐ones 28a and 3‐exo‐ 28b , respectively. Rearrangement of these compounds in the presence of Ac₂O/AcONa lead to the formation of the corresponding 3‐(phenylsulfonyl)benzo[a]heptalene‐1,2‐diol diacetates 30a and 30b , which on treatment with MeONa/MeI gave the corresponding MeO‐substituted compounds 31a and 31b . The reductive elimination of the PhSO₂ group led finally to the 1,2‐dimethoxybenzo[a]heptalenes 32a and 32b . Deprotonation experiments of 32a with t‐BuLi/N,N,N′,N′‐tetramethylethane‐1,2‐diamine (tmeda) and quenching with D₂O showed that the most acid C? H bond is H? C(3) (Scheme 9). Some of the new structures were established by X‐ray crystal‐diffraction analyses (cf. Figs. 1, 3, 4, and 5). Moreover, nine of the new benzo[a]heptalenes were resolved on an anal. Chiralcel OD‐H column, and their CD spectra were measured (cf. Figs. 8 and 9). As a result, the 1,2‐dimethoxybenzo[a]heptalenes 32a and 32b showed unexpectedly new Cotton‐effect bands just below 300 nm, which were assigned to chiral exciton coupling between the heptalene and benzo part of the structurally highly twisted compounds. The PhSO₂‐substituted benzo[a]heptalenes 30b and 31b showed, in addition, a further pair of Cotton‐effect bands in the range of 275–245 nm, due to chiral exciton coupling of the benzo[a]heptalene chromophore and the phenylsulfonyl chromophore (cf. Fig. 10).     

Benzo[a]heptalenes from Heptaleno[1,2‐c]furans. Part I

It is shown that heptaleno[1,2‐c]furans 1 , which are available in two steps from heptalene‐4,5‐dicarboxylates by reduction and oxidative dehydrogenation of the corresponding vicinal dimethanols 2 with MnO₂ or IBX (Scheme 4), react thermally in a Diels–Alder‐type [4+2] cycloaddition at the furan ring with a number of electron‐deficient dipolarophiles to yield the corresponding 1,4‐epoxybenzo[d]heptalenes (cf. Schemes 6, 15, 17, and 19). The thermal reaction between dimethyl acetylenedicarboxylate (ADM) and 1 leads, kinetically controlled, via a sterically less‐congested transition state (Fig. 4) to the formation of the (M*)‐configured 1,4‐dihydro‐1,4‐epoxybenzo[a]heptalenes, which undergo a cyclic double‐bond shift to the energetically more‐relaxed benzo[d]heptalenes 4 (Schemes 6 and 7). Most of the latter ones exhibit under thermal conditions epimerization at the axis of chirality, so that the (M*)‐ and (P*)‐stereoisomers are found in reaction mixtures. The (P*)‐configured forms of 4 are favored in thermal equilibration experiments, in agreement with AM1 calculations (Table 1). The relative (P*,1S*,4R*)‐ and (M*,1S*,4R*)‐configuration of the crystalline main stereoisomers of the benzo[d]heptalene‐2,3‐dicarboxylates 4a and 4f , respectively, was unequivocally established by an X‐ray crystal‐structure determination (Figs. 1 and 2). Acid‐induced rearrangement of 4 led to the formation of the corresponding 4‐hydroxybenzo[a]heptalene‐2,3‐dicarboxylates 5 in moderate‐to‐good yields (Schemes 8, 13, and 14). When the aromatization reaction is performed in the presence of trifluoroacetic acid (TFA), trifluoroacetates of type 6 and 13 (Schemes 8, 12, and 13) are also formed via deprotonation of the intermediate tropylium ions of type 7 (Scheme 11). Thermal reaction of 1 with dimethyl maleate gave the 2,3‐exo‐ and 2,3‐endo‐configured dicarboxylates 14 as mixtures of their (P*)‐ and (M*)‐epimers (Scheme 15). Treatment of these forms with lithium di(isopropyl)amide (LDA) at ?70° gave the expected benzo[a]heptalene‐2,3‐dicarboxylates 15 in good yields (Scheme 16). Fumaronitrile reacted thermally also with 1 to the corresponding 2‐exo,3‐endo‐ and 2‐endo,3‐exo‐configured adducts 17 , again as mixtures of their (P*)‐ and (M*)‐epimers (Scheme 17), which smoothly rearranged on heating in dimethoxyethane (DME) in the presence of Cs₂CO₃ to the benzo[a]heptalene‐2,3‐dicarbonitriles 18 (Scheme 18). Some cursory experiments demonstrated that hex‐3‐yne‐2,5‐dione and (E)/(Z)‐hexa‐3‐ene‐2,5‐dione undergo also the Diels–Alder‐type cycloaddition reaction with 1 (Scheme 19). The mixtures of the stereoisomers of the 2,3‐diacetyl‐1,4‐epoxytetrahydrobenzo[d]heptalenes 22 gave, on treatment with Cs₂CO₃ in DME at 80°, only mixtures of the regioisomeric inner aldol products 24 and 25 of the intermediately formed benzo[a]heptalenes 23 (Scheme 20).     

Synthesis of Pyrazolo[1,5‐a][1,3,5]triazine,Pyrazolo[1,5‐a]pyrimidine,and Imidazo[1,2‐b]pyrazole Derivatives Based on Imidazo[2,1‐b]thiazole Moiety

3(5)‐Aminopyrazole derivative ( 6 ) has been synthesized by the reactions of the versatile unreported 2‐cyano‐N ′‐(1‐(3‐methyl‐6‐phenylimidazo[2,1‐b ]thiazol‐2‐yl)ethylidene)acetohydrazide ( 3 ) with phenyl isothiocyanate in KOH/DMF solution followed by reaction with methyl iodide and hydrazine hydrate. Reaction of compound 6 with some 1,3‐dicarbonyl compounds yielded pyrazolo[1,5‐a ]pyrimidine derivatives ( 14 – 17 ). Alkylation of compound 6 with various halo reagents, followed by intramolecular cyclization, yielded the corresponding imidazo[1,2‐b ]pyrazole derivatives 27 , 29 , 31 , and 33 . All newly synthesized compounds were elucidated by considering the data of both elemental analysis and spectral data.     

Imidazo[2,1‐b]thiazoles,imidazo[2,1‐b]imidazoles and Pyrrolo[1,2‐c]imidazoles. synthesis,structure and evaluation of benzodiazepine receptor binding

As a continuation of our studies on bicyclic heterocycles with benzodiazepine receptor affinity, derivatives with a 5:5 bicyclic skeleton, namely imidazo[2,1‐b]thiazoles, imidazo[2,1‐b]imidazoles and pyrrolo[1,2‐c]imidazoles were prepared. The compounds possessed an aromatic substituent with different spatial arrangement and distance to the bicyclic skeleton. X‐ray structure analysis was performed for Z‐2‐(4‐chlorobenzylidene)‐5,5‐diphenyl‐2,3,5,6‐tetrahydroimidazo[2,1‐b]imidazoline‐3,6‐dione ( 6a ) and 5‐amino‐6‐cyano‐7‐phenyl‐1‐oxo‐3‐thioxo‐2,3‐dihydro‐1H‐pyrrolo[1,2‐c]imidazole ( 20a ). In contrast to the previously described arylideneimidazo[2,1‐b]thiazepinones the smaller heterocyclic ring systems investigated in this study were devoid of meaningful benzodiazepine receptor affinity as well as anti‐convulsant activity.     

Synthesis of novel pyrazolo[3,4‐d]pyridazine,pyrido[1,2‐a]benzimidazole,pyrimido[1,2‐a]benzimidazole and triazolo[4,3‐a]pyrimidine derivatives

4‐Acetyl‐5‐methyl‐1‐phenyl‐1H‐pyrazole reacts with dimethylformamide dimethylacetal (DMF‐DMA) to afford the corresponding (E)1‐(5‐methyl‐1‐phenyl‐1H‐pyrazol‐4‐yl)‐3‐(N,N‐dimethylamino)‐2‐propen‐1‐one. The latter product undergoes regioselective 1,3‐dipolar cycloaddition with nitrilimines and nitrile oxides to afford the novel 3‐aroyl‐4‐(5‐methyl‐1‐phenyl‐1H‐pyrazol‐4‐yl)carbonyl‐1‐phenylpyrazole and 3‐aroyl‐4‐(5‐methyl‐1‐phenyl‐1H‐pyrazol‐4‐yl)carbonyl isoxazole derivatives, respectively. It reacts also with 1H‐benzimidazole‐2‐acetonitrile, 2‐aminobenzimidazole and 3‐amino‐1,2,4‐triazole to afford the novel pyrido[1,2‐a]benzimidazole, pyrimido[1,2‐a]benzimidazole and the triazolo[4,3‐a]pyrimidine derivatives, respectively. The reaction of 3‐aroyl‐4‐(5‐methyl‐1‐phenyl‐1H‐pyrazol‐4‐yl) carbonyl‐1‐phenylpyrazole derivatives with hydrazine hydrate led to a new pyrazolo[3,4‐d]pyridazine derivatives.     

One‐pot Synthesis of Benzo[4,5]imidazo[1,2‐a]pyridine Derivatives in Aqueous Conditions

One‐pot reaction of cyclic 1,3‐diketones, dimethylformamide dimethylacetal (DMFDMA) and 2‐(1H‐benzo[d ]imidaz‐2‐yl)acetonitrile was found to be a highly selective process leading to 4‐oxo‐1,2,3,4‐tetrahydrobenzo[4,5]imidazo[1,2‐a ]quinolin‐6‐yl cyanides. Optimized reaction conditions using water as solvent at room temperature or under microwave heating allowed high yields of the target products required no additional purification.     

Spiro[pyrido[3,2,1‐ij]pyrimido[4,5‐b]quinoline‐7,5′‐pyrrolo[2,3‐d]pyrimidines] and Spiro[pyrimido[4,5‐b]quinoline‐5,1′‐pyrrolo[3,2,1‐ij]quinolines] Derived from 5,6‐Dihydro‐4H‐pyrrolo[3,2,1‐ij]quinoline‐1,2‐dione

Reaction of 5,6‐dihydro‐4H‐pyrrolo[3,2,1‐ij]quinoline‐1,2‐dione ( 1 ) with two equivalents of some 6‐aminouracils (or 6‐amino‐2‐thiouracil) generates spirocyclic tetrahydrobenzo[if]quinolizines ( 7 ). The one‐pot, three‐component reaction of amido ketone ( 1 ) with 6‐aminouracil (or 6‐amino‐2‐thiouracil) and a cyclic six‐membered 1,3‐diketone produces spirocyclic tetrahydropyrrolo[3,2,1‐ij]quinolinones ( 15 ).     

A Mild and Efficient Synthesis of Novel Isoxazolyl‐Benzo[d]Pyrazino[2,1‐b] [1,3]Oxazoles

Synthesis of novel 2‐3‐methyl‐5‐[(E)‐2‐aryl‐1‐ethenyl]‐4‐isoxazolyl‐4,10a‐diaryl‐1,10a‐dihydro‐2H‐benzo[d]pyrazino[2,1‐b][1,3]oxazoles 5 were simply achieved by the reaction of 2‐[3‐methyl‐5‐[(E)‐2‐aryl‐1‐ethenyl]‐4‐isoxazolyl(2‐oxo‐2‐arylethyl)amino]‐1‐aryl‐1‐ethanones 3 with o‐aminophenol 4 in the presence of CAN catalyst. The intermediates, 2‐[3‐methyl‐5‐[(E)‐2‐aryl‐1‐ethenyl]‐4‐isoxazolyl(2‐oxo‐2‐arylethyl)amino]‐1‐aryl‐1‐ethanones 3 , were prepared by the reaction of 4‐amino‐3‐methyl‐5‐styrylisoxazole 1 , with phenacylbromides 2 in ethanol in the presence of K₂CO₃. The structures of the newly synthesized compounds 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l and 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 5k , 5l have been confirmed by analytical and spectral data.     

Efficient New Synthesis of N‐Arylbenzo[b]furo[3,2‐d]pyrimidin‐4‐amines and Their Benzo[b]thieno[3,2‐d]pyrimidin‐4‐amine Analogues via a Microwave‐Assisted Dimroth Rearrangement

A useful and rapid access to libraries of N‐arylbenzo[b]furo[3,2‐d]pyrimidin‐4‐amines ( 1 ) and their novel benzo[b]thieno[3,2‐d]pyrimidin‐4‐amine analogues ( 2 ) was investigated for the first time. Title compounds were obtained via microwave‐accelerated condensation and Dimroth rearrangement of suitable anilines with N′‐(2‐cyanaryl)‐N,N‐dimethylformimidamides obtained by reaction of benzo[b]furane and benzo[b]thiophene precursors with N,N‐dimethylformamide dimethyl acetal. This work also demonstrates that well‐controlled parameters offer comfortable use of microwave technology and are both safe and beneficial to the environment. Some products obtained in this article exhibit interesting in vitro antiproliferative effects.     

Synthesis of 6‐Aryl‐4H‐imidazo[1,2‐b][1,2,4]triazoles and 6‐Aryl‐thiazolo[3,2‐b][1,2,4]triazoles

The cyclization of the derivatives of 3‐aminotriazole, 2‐(5‐substituted 4H‐1,2,4‐triazol‐3‐ylamino)‐1‐arylethanones and 2‐(4H‐1,2,4‐triazol‐3‐ylthio)‐1‐arylethanones to yield 6‐aryl‐4H‐imidazo[1,2‐b][1,2,4]triazoles and 6‐aryl‐thiazolo[3,2‐b][1,2,4]triazoles has been described.     

Synthesis,characterization, and antidiabetic activity of 6‐methoxyimidazo[1,2‐b]pyridazine derivatives

The present article describes the synthesis, characterization, and antidiabetic activity of 6‐methoxyimidazo[1,2‐b]pyridazine derivatives 7a‐l . The synthetic sequence for the preparation of these derivatives involves the following prominent reactions: (a) Step 1: involves the high‐pressure amination reaction; (b) Step 2: involves the Zinc oxide nanoparticle‐catalyzed cyclization reaction; (c) Step 3: involves the methoxylation; (d) Step 4: involves the bromination reaction; (e) Step 5: involves the Suzuki coupling reaction; (f) Step 6: involves the reduction of the –NO₂ group; (g) Step 7: involves Boc protection of the 1^o amino group (h) Step 8: involves diazotization of the amine group and finally the last of the synthesis (i) Step 9: involves the saponification of the ethyl ester group. Furthermore, the structures of the newly synthesized 6‐methoxyimidazo[1,2‐b]pyridazine derivatives 7a–l were determined using ¹H NMR, ¹³C NMR, and Mass and IR spectroscopic analyses. These derivatives were evaluated for their antidiabetic property and the results revealed that most of the compounds exhibited significant potency. It is worth mentioning that compounds 7b (69.87%), 7f (69.0%), 7h (68.79%), and 7l (68.61%) with substitution R = para‐NH₂, para‐COOH, meta‐NH₂, and meta‐COOH, respectively, showed significant (good) hypoglycemic activity when compared to the standard drug insulin (50 mg/kg b.w) in reducing the blood glucose level.     

Useful Precursors for Synthesis of Some New Azolo[3,4‐d]pyridiazines,Azolo[1,5‐a]pyrimidines,Azolo[5,1‐c]triazines,Pyrazoles, and Benzo[b][l,4]diazepine

Pyrazolo[3,4‐d]pyridazines, isoxazolo[3,4‐d]pyridazines, azolo[1,5‐a]pyrimidines, azolo[5,1‐c]triazines, pyrazoles, and benzo[b][l,4]diazepine were synthesized from the appropriate hydrazonoyl halides, hydroximoyl halides, heterocyclic amines, diazotized heterocyclic amines, arenediazonium chlorides, and o‐phenylenediamines with appropriate of sodium 3‐(5‐bromobenzofuran‐2‐yl)‐3‐oxoprop‐1‐en‐1‐olate or 1‐(5‐bromobenzofuran‐2‐yl)‐3‐(dimethylamino)prop‐2‐en‐1‐one. The newly synthesized compounds were elucidated by elemental analyses, spectral data, and alternative synthesis whenever possible.     

Azulene–Naphthalene‐Type Rearrangements in Benz[a]azulene and Cyclohepta[b]indole

Flash vacuum pyrolysis (FVP) of benz[a]azulene yields phenanthrene and 2‐ethynylbiphenyl. FVP of cyclohepta[b]indole similarly yields phenanthridine and 2‐cyanobiphenyl. The reversibility of the reactions is demonstrated by FVP of 2‐ethynylbiphenyl and 2‐isocyanobiphenyl. All the observed reactions are in accord with the norcaradiene–vinylidene mechanism of the azulene–naphthalene rearrangement, whereas other proposed mechanisms are ruled out.     

On the chemistry of 5‐aryl‐2‐hydrazino‐benzo[6,7]cyclohepta[1,2‐b]pyrido[2,3‐e] pyrimidin‐4‐one

Several pyrido[2,3‐e]pyrimidine fused with other rings have been prepared by intramolecular cyclization of 5‐(4‐chlorophenyl)‐2‐hydrazino‐benzo [6,7]cyclohepta‐[1,2‐b]pyrido[2,3‐e]pyrimidine‐4‐one ( 1 ) with acids, carbon disulfide to form triazole derivatives ( 2,4 ), halo‐ketones to give triazine derivative ( 5 ), β‐ketoesters, β‐cyanoesters, and β‐diketones to yield 2‐(1‐pyrazolyl) derivatives ( 7,9,10 ), and aldehydes to form arylhydrazone derivatives ( 11a,b ) which cyclized to form triazoles ( 12a,b ). Also, acyclic N‐nucleosides are prepared by heating under reflux 2‐hydrazino‐benzo[6,7]cyclohepta[1,2‐b]pyrido[2,3‐e] pyrimidin‐4‐one ( 1 ) with xylose and glucose to give the corresponding acyclic N‐nucleosides ( 13a,b ) which are cyclized to afford the corresponding protected tetra and penta–O‐acetate C‐nucleosides ( 14a,b ). Deacetylating of the latter nucleosides afforded the free acyclic C‐nucleosides ( 15a,b ). © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:34–43, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20248     

Benzo[1,2‐c:3,4‐c']bis[1,2,5]selenadiazole, [1,2,5]selenadiazolo‐[3,4‐e]‐2,1,3‐benzothiadiazole,furazanobenzo‐2,1,3‐thiadiazole,furazanobenzo‐2,1,3‐selenadiazole and related heterocyclic systems

The first synthesis of benzo[1,2‐c:3,4‐c']bis[1,2,5]selenadiazole has been developed starting from commercially available 4‐nitrobenzo‐2,1,3‐selenadiazole. Improved syntheses of the related heterocycles [1,2,5]selenadiazolo[3,4‐e]‐2,1,3‐benzothiadiazole, furazanobenzo‐2,1,3‐thiadiazole and furazanobenzo‐2,1,3‐selenadiazole are also reported.     

Facile Route to Novel Pyrazolo[3,4‐d]pyrimidine,Imidazo[1,2‐b] pyrazole,Pyrazolo[3,4‐d][1,2,3]triazine,Pyrazolo[1,5‐c][1,3,5]triazine and Pyrazolo[1,5‐c][1,3,5]thiadiazine Derivatives

A regioselective synthesis of novel pyrazolo[3,4‐d]pyrimidines, imidazo[1,2‐b]pyrazoles, pyrazolo[3,4‐d][1,2,3]triazine, pyrazolo[1,5‐c][1,3,5]triazine and pyrazolo[1,5‐c][1,3,5]thiadiazine incorporating a thiazole moiety was described via the reactions of the versatile, readily accessible 5‐amino‐3‐(phenylamino)‐N‐(4‐phenylthiazol‐2‐yl)‐1H‐pyrazole‐4‐carboxamide ( 1 ) with each of DMF‐DMA, phenylisothiocyanate, chloroacetyl chloride, phenacyl bromide, benzoylisothiocyanate and formalin, respectively. All structures of the newly synthesized compounds were elucidated by elemental analysis and spectral data.