Microwave assisted synthesis of novel imidazo [2,1-b]thiazole derivative attached to quinoxalinones

3-(6-Phenylimidazo[2,1-b]thiazol-5-yl)quinoxalin-2(1H)-ones (qunoxalinone) (6a-q) have been synthesized by the reaction of ethyl 2-oxo-2-(6-phenylimidazo[2,1-b]thiazol-5-yl)acetates (4a-e) with suitably substituted o-phenylenediamines (5a-f) under microwave heating. The ethyl 2-oxo-2-(6-phenylimidazo[2,1-b]thiazol-5-yl)acetates (4a-e) were prepared by the reaction of 6-phenylimidazo[2,1-b]thiazoles (3a-e) with ethyl chlorooxoacetate in refluxing 1,4-dioxane whereas the thiazoles (3a-e) were synthesized by the reaction of 2-bromo-1-phenylethanones (2a-e) with thiazol-2-amine in refluxing acetone.     

From N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine to propeller-shaped N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)-amine: syntheses and structures

Three unique propeller-shaped helicenyl amines compounds: N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine (1), N-phenyl-N,N-di(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (2), and N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (3) were efficiently synthesized by Wittig reaction and oxidative photocyclization. The crystal structures of 1, 2 and molecular configuration optimization (DFT-B3LYP/6-31+G(d)) of 3 reveal that the steric hindrance from the moiety of trithia[5]helicene effectively forces the nitrogen atom and the three bonded carbon atoms to coplanar and the interplanar angles of the facing terminal thiophene ring and benzene ring becoming larger when the helical arm increased from 1 to 3. Electrochemical properties and UV–vis absorption behaviors of 1, 2, 3 were primarily determined by the moiety of trithia[5]helicene.     

Microwave-assisted Hantzsch thiazole synthesis of N-phenyl-4-(6-phenylimidazo[2,1-b]thiazol-5-yl)thiazol-2-amines from the reaction of 2-chloro-1-(6-phenylimidazo[2,1-b]thiazol-5-yl)ethanones and thioureas

N-Phenyl-4-(6-phenylimidazo[2,1-b]thiazol-5-yl)thiazol-2-amines (6a-q) have been synthesized by the Hantzsch thiazole reaction of 2-chloro-1-(6-phenylimidazo[2,1-b]thiazol-5-yl)ethanones (4a-e) with suitably substituted thioureas using microwave heating. The ethanones (4a-e) were prepared by the reaction of 6-phenylimidazo[2,1-b]thiazoles (3a-e) with chloroacetylchloride in refluxing 1,4-dioxane whereas the thiazoles (3a-e) were synthesized by the reaction of 2-bromo-1-phenylethanones (2a-e) with thiazol-2-amine in refluxing acetone.     

Ophiuroidine, the first indolo[2,1-b]quinazoline alkaloid from the Caribbean brittle star Ophiocoma riisei

A new indoloquinazoline alkaloid, ophiuroidine 1, having an indolo[2,1-b]quinazoline-6,12-dione skeleton, was isolated from the Caribbean ophiuroid, Ophiocoma riisei. The structure of 1 was determined as 4,8,9-trihydroxyindolo[2,1-b]quinazoline-6,12-dione from spectroscopic data. Ophiuroidine 1 is the first example of an indoloquinazoline alkaloid found in a marine invertebrate.     

Facile synthesis of regio-isomeric naphthofurans and benzodifurans

Naphtho[1,2-b]furans 1a-f, naphtho[2,1-b]furans 2a-f, benzo[1,2-b:5,4-b′]difurans 3a-b, benzo[1,2-b:4,5-b′]difurans 4a-b, and benzo[1,2-b:4,3-b′]difurans 5a-b were synthesized by base-catalyzed cyclization reaction of the corresponding o-alkoxybenzoylarene derivatives. The o-alkoxybenzoylarenes were obtained from the etherification reaction of the o-hydroxybenzoylarenes, which were prepared either by the reaction of methoxyarenes with benzoyl chloride in the presence of aluminum chloride or by photo-Fries rearrangement of aryl benzoates.     

Synthesis and photochromic behaviour of new methyl induced linear and angular thieno-2H-chromenes

New methyl induced linear and angular thieno-2H-chromenes 4, 5 and 6 were prepared by reaction of new methylated 6-hydroxybenzo[b]thiophenes 2 (a, b and c) and propargylic alcohols 3a and 3b, using acidic Alumina Brockmann I as catalyst and drying agent. Compounds 2 were prepared in good to excellent yields in a ‘one pot’ three step reaction from the corresponding bromo compounds 1. The photochromic behaviour of compounds 4, 5 and 6b was evaluated with the aid of a classical set of spectrokinetic parameters, and compared to reference compounds that are benzoannellated in the 5,6 and 6,7 positions of the chromene (naphthopyrans) and also to thieno-2H-chromenes 7 and 8, previously prepared, which are analogues of 5a. The resistance to fatigue (photodegradation) under continuous irradiation was also evaluated.     

Synthesis of 4-substituted azepino[3,4-b]indole-1,5-diones

Mono- or dibromo derivatives 2 and 3 were prepared by an efficient two-step route from 10-methyl-azepino[3,4-b]indole-1,5-dione 1. Elimination reaction on 2 gave access to 4-bromo-10-methyl-2H,10H-azepino[3,4-b]indole-1,5-diones 4. Finally, 4-substituted 10-methyl-2H,10H-azepino[3,4-b]indole-1,5-diones 6-14 were synthesised in good yields from 4 via palladium-mediated cross-coupling reactions.     

Chemistry of cyclopropenones: synthesis of new pyrrolo[2,1-b]-1,3,4-oxadiazoles

2,3-Diphenylcyclopropenone (1) reacts with ylidene-N-phenylhydrazine-carbothioamides 2a-e to form the pyrrolo[2,1-b]-1,3,4-oxadiazoles 5a-e.     

Carbenoid induced irreversible ring opening of naphthopyrans

Contrary to expectation rhodium carbenoids do not undergo cycloaddition to the 2H-pyran unit of the isomeric naphthopyrans 3 and 5. With 3, a naphtho[2,1-b]pyran-8-ylacetate, 4 is formed and a novel merocyanine dye 6 results from a cycloaddition across the C-5-C-6 double bond of the naphtho[1,2-b]pyran 5. Tethering the carbenoid to the naphtho[1,2-b]pyran system 5, as in 10, results in a similar mode of addition and affords the intensely coloured tetracycle 11.     

Zinc triflate-catalyzed synthesis of pyrazino[2,1-b]quinazoline-3,6-diones

Using zinc triflate, the direct one-pot double cyclodehydration of linear tripeptides to the total synthesis of pyrazino[2,1-b]quinazoline-3,6-diones (1a-l) on solid support was achieved with good overall yields in short reaction time. These syntheses of the pyrazino[2,1-b]quinazoline-3,6-diones were conveniently achieved in only three steps, starting from the amino acid-bound Wang resin.     

Alternative synthesis and novel oxidizing ability of 6,9-disubstituted cyclohepta[b]pyrimido[5,4-d]pyrrole-8(6H),10(9H)-dione derivatives

Synthesis of 6,9-disubstituted cyclohepta[b]pyrimido[5,4-d]pyrrole-8(6H),10(9H)-diones 7a-g was accomplished by ring opening and ring closure sequences of 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8,10(9H)-dione derivatives induced by several amines. Furthermore, alternative synthetic methodology for compounds 7a-e was also accomplished by single-step reaction of 2-chlorotropone with 6-aminouracil derivatives under mild conditions. X-ray crystal analysis of 7a was carried out to clarify the structural characteristics. The properties of 7a-e were studied by the UV-vis spectra and reduction potentials (−1.24 to −1.39 V vs Ag/AgNO₃). Novel photo-induced oxidation reaction of 7a-d toward some amines under aerobic conditions was carried out to give the corresponding imines in more than 100% yield [based on compounds 7a-d], suggesting the oxidation reaction occurs in an autorecycling process.     

Synthesis and characterization of 2H-pyrano[3,2-c]coumarin derivatives and their photochromic and redox properties

A series of 2H-pyrano[3,2-c]chromen-5-one derivatives were synthesized and characterized. Their photochromic and redox properties were investigated by the UV-vis absorption spectroscopy. While compounds with one or two phenyl groups incorporated at the 2-position were present in both ring-opened (5a and 10a) and ring-closed (6a and 11a) forms, the incorporation of an N,N-dimethylamino group on either side of the aromatic ring resulted in formation of the ring-opened (5b and 10b) forms only. The ring-closed forms 13 and 18 with a methyl substituent at the 3-position of the pyran moiety failed to exhibit photochromic behavior. Compound 23 with an N,N-dimethylamino group on the aromatic ring displayed increasing shoulder absorption in the visible region and a distinct change of color upon UV irradiation. The non-fluorescent 10b instantly changed from dark red to colorless, when treated with sodium borohydride. The reduced 28 was blue fluorescent with a quantum yield of 0.46 and could be returned to its original color via DDQ oxidation.     

Solvent-free sonochemical one-pot three-component synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11-triones and 1H-pyrazolo[1,2-b]phthalazine-5,10-diones

A rapid and efficient one-pot three-component protocol for the synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11-triones 4 and 1H-pyrazolo[1,2-b]phthalazine-5,10-diones 6 has been developed by domino coupling of phthalhydrazide, 1,3-diketones, and aldehydes under solvent-free conditions at 80 °C as well as under solvent-free ultrasound irradiation at room temperature promoted by (S)-camphorsulfonic acid.     

New efficient synthesis of 2,3,4-trisubstituted 3,4-dihydroquinazolines by a Ugi 4CC/Staudinger/aza-Wittig sequence

A series of 2,3,4-trisubstituted 3,4-dihydroquinazoline 3 was prepared by intramolecular aza-Wittig reaction of amide carbonyl groups with methyldiphenyl iminophosphorane, which was obtained from a Ugi 4CC/Staudinger sequence. Further intramolecular Heck reaction of 3d′-g′ in the presence of catalytic amount of Pd(OAc)₂ gave 6,12-dihydroindolo[2,1-b]quinazolines 4a-d in good yields.     

A rapid and convenient synthesis of novel 1-imino-2,3-dihydro-1H-pyrazino[2,1,-b]quinazolin-5-ones

Exploring original approaches for the synthesis of therapeutic agents having a quinazoline part, we discovered that novel 3,4-dihydro-2H-pyrazino[2,1,-b]quinazolines (3) may be rapidly and easily obtained via the chemistry of 4,5-dichloro-1,2,3-dithiazolium chloride (1). Our synthetic approach of this reaction is described with the aim of obtaining a well-controlled access to this very rarely described pyrazino[2,1,-b]quinazoline skeleton.     

Functionalization of ‘kite’ shaped styryl end-capped benzodithiophene with ketone groups: synthesis, characterization and properties

We report the synthesis of a new bridged end-capped distyryldithiophene with ketone groups on the bridge: E,E-2,7′-bis((2-phenyl)-ethenyl)-benzo[2,1-b:3,4-b′]dithiophene-4,5-dione 1. Optical and electrochemical properties of 1 in solution were investigated by UV-vis absorption and cyclic voltammetry and compared to the unsubstituted parent molecule (KDS2T). Morphology of 1-based thin films was investigated by scanning electron microscopy (SEM) and the crystalline structure characterization by X-ray diffraction (XRD). Thin films were implemented as active layers into organic thin-film transistors (OTFT) in top contact configuration to evaluate the charge transport properties.     

Regioselective synthesis of 2,5-dihydro-4H-pyrazolo[4,3-c]quinolin-4-ones by the cyclization of 3-acyl-4-methoxy-1-methylquinolinones with hydrazines

Reaction of 3-acyl-4-methoxy-1-methylquinolinones 2 and 5 with hydrazines has been investigated under different experimental conditions. Compound 2 always gave rise selectively and exclusively to the regioisomeric 1,3-disubstituted- or 2,3-disubstituted-pyrazolo[4,3-c]quinolin-4(5H)one (compounds 3a,b or 4a,b, respectively), while reaction of 5 with N-methylhydrazine led to a mixture of pyrazoles 7a and 8a. With N-phenylhydrazine, compounds 7b or 8b were regioselectively obtained. Compound 8a could be selectively synthesized working in solventless conditions. Structural elucidation of all products was independently achieved by NMR spectroscopy.     

Regioselective synthesis of fused benzopyrazolo[3,4-b]quinolines under solvent-free conditions

New 6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinolines 6 have been obtained in a novel solvent-free three-component reaction involving β-tetralone along with 5-aminopyrazoles 1 and benzaldehydes 2. The isomeric 6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinolines 9 could not be prepared in a similar fashion directly from α-tetralone, but were obtained by the reaction of amines 1 with benzylidene-derivative 10 of α-tetralone in similar conditions. The yields of quinolines obtained via this novel protocol were good and the reaction times varied from few minutes to just few seconds.     

Tunable blue-emitting fluorophores—benzo[1,2-b:4,3-b′]dithiophene and trithia[5]helicene end-capped with electron-rich or electron-deficient aryl substituents

Light-emitting fluorophores 1-10b based on aryl substituted benzo[1,2-b:4,3-b′]dithiophenes (BDT) and trithia[5]helicenes (T5H) have been synthesized using various combinations of Suzuki coupling, the Wittig, or McMurry reaction, and subsequent photocyclization of the dithienylethenes thus obtained. Photophysical properties of the helical compounds end-capped with different electron-rich and electron-deficient aryl moieties thus resulting were evaluated. Photocyclization of a dithienylethene derivative 10a was investigated, and the X-ray crystal structure of dinaphthyl-substituted BDT (4) was obtained. With this series of compounds 1-10b, we demonstrate that the optical properties of all of the new compounds, and by extension many conjugated materials, can be tuned over the entire blue range (400-480 nm).     

Synthesis and single-crystal X-ray diffraction analysis of new heterocyclic coloured materials. 3-Arylazo-8H-imidazo[1,2-b] pyrazolo[4,3-d]pyridazines

A simple synthetic strategy is described for the hitherto unreported 3-arylazo-8H-imidazo[1,2-b]pyrazolo[4,3-d]pyridazines 7 is described based on the reaction of 3-acetyl-4-cyano-1,5-diphenylpyrazole hydrazone 3 with the hydrazonoyl halides 1a-l. The structures of such dyes were confirmed by spectroscopic and X-ray crystallographic analyses. The mechanism of formation of such compounds was also discussed.