2-Benzyliden-2H-thieto[3,2-b]quinoline: a new heterocycle and its rearrangement to 2-phenylthieno[3,2-b]quinoline

Synthesis of the strained 2H-thieto[3,2-b]quinoline ring system is reported for the first time. Treatment of (Z)-2-benzyliden-2H-thieto[3,2-b]quinoline derivatives of this heterocycle with base, at reflux in ethanol, causes a novel rearrangement to 2-phenylthieno[3,2-b]quinolines. Indeed, the one-pot reaction of 2-aminobenzaldehydes and (Z)-2-benzylidenethietan-3-one in refluxing basic ethanol leads directly to 2-phenylthieno[3,2-b]quinolines in good yields.     

Preparation of novel pyridine-fused tris-heterocycles; pyrido[4,3-e]pyrrolo-/pyrido[4,3-e]furano[2,3-c]pyridazines and pyrido[3,4-b]pyrrolo[3,2-d]pyrrole

Three novel pyrido-fused tris-heterocycles have been prepared based on a Suzuki coupling and subsequent cyclisation approach. Pyrido[4,3-e]pyrrolo[2,3-c]pyridazine (3b, 77%) and pyrido[4,3-e]furano[2,3-c]pyridazine (5b, 76%) were obtained by intramolecular diazocoupling. Successful diazocoupling of furan (5b) is thus reported for the first time by NOBF₄ generation of the diazonium intermediate. N-TIPS-pyrido[3,4-b]pyrrolo[3,2-d]pyrrole (TIPS-4b) was synthesised by thermal cyclisation of pyridyl nitrene in considerably higher yield (71%) than previously experienced from similar cyclisations, due to TIPS-activation.     

Intramolecular 4+2 cycloaddition of thieno[2,3-e][1,2,4]triazines: routes towards condensed thieno[2,3-b]pyridines

Synthetic approaches towards new condensed thienopyridine ring systems including furo[2,3-b]thieno[3,2-e]pyridines, bisthieno[2,3-b:3′,2′-e]pyridines, 5H-chromeno[2,3-b]thieno[3,2-e]pyridines, 5H-benzo(f)chromeno[2,3-b]thieno[3,2-e]pyridines have been achieved by application of intramolecular 4+2 cycloaddition reactions of suitably designed thieno[2,3-e][1,2,4]triazines tethered with alkene or alkyne terminals.     

Synthesis of 9-nitro-5H-spiro[benzo[b]tetrazolo[1,5-d][1,4]oxazepine-4,2′-oxirane] via an unusual ring-expansion

Attempted cyclization of (4-(hydroxymethyl)-8-nitro-4H-benzo[b]tetrazolo[1,5-d][1,4]oxazin-4-yl)methyl 4-methylbenzenesulfonate 2 did not give the expected spirooxetane product 1, but instead provided 9-nitro-5H-spiro[benzo[b]tetrazolo[1,5-d][1,4]oxazepine-4,2′-oxirane] 3via an unusual ring-expansion process. The structure of compound 3 was confirmed by single-crystal X-ray crystallography. The spiroepoxide (oxirane) in compound 3 could be ring-opened with a variety of nucleophiles to give products of potential interest to medicinal chemists.     

An efficient synthesis of spiro[dibenzo[b,i]xanthene-13,3′-indoline]-pentaones and 5H-dibenzo[b,i]xanthene-tetraones

Spiro[dibenzo[b,i]xanthene-13,3′-indoline]-pentaones and 5H-dibenzo[b,i]xanthene-tetraones are synthesized from the condensation of 2-hydroxynaphthalene-1,4-dione with isatins or aldehydes.     

Benzo[b]thiophen-3(2H)-one 1,1-dioxide—a versatile reagent in the synthesis of spiroheterocycles

New applications of benzo[b]thiophen-3(2H)-one 1,1-dioxide have been investigated. The synthesis of a new heterocyclic system 3H,2′H-spiro[benzo[b]thieno[3,2-b]pyridine-3,2′-benzo[b]thiophene] is described and a mechanism for the cyclisation is proposed.     

An efficient ionic liquid mediated synthesis of substituted 5H[1,3]-thiazolo[2,3-b]quinazoline-3,5-(2H)-dione and 5H-thiazolo[2,3-b]quinazolin-5-one

A new, environmentally benign two-step synthesis of 5H[1,3]-thiazolo[2,3-b]quinazoline-3,5-(2H)-dione and 5H-thiazolo[2,3-b]quinazolin-5-one derivatives has been accomplished stepwise. The substituted 2-aminobenzoic acid upon condensation with thiourea in 1-butyl-3-methylimidazolium bromide at moderate temperature under nitrogen atmosphere yielded 2-thioxo-1H-4-quinazolinones. The resulting intermediate 2-thioxo-1H-4-quinazolinones, when reacted with 2-chloroethanoic acid/2-chloropropanal underwent cyclization to yield the desired product in excellent yields.     

Synthesis of 2,5-dihydrobenzo[b]oxepines and 5,6-dihydro-2H-benzo[b]oxocines based on a ‘[3+3] cyclization-olefin-metathesis’ strategy

Functionalized 2,5-dihydrobenzo[b]oxepines and 5,6-dihydro-2H-benzo[b]oxocines were prepared based on a ‘[3+3] cyclization-olefin-metathesis’ strategy.     

Synthesis of 2,5-dihydrobenzo[b]oxepins and 5,6-dihydro-2H-benzo[b]oxocines based on [3+3] cyclizations of 1,3-bis(silyl enol ethers)

Functionalized 2,5-dihydrobenzo[b]oxepins and 5,6-dihydro-2H-benzo[b]oxocines were prepared based on a ‘[3+3] cyclization-olefin-metathesis’ strategy.     

Convenient synthesis of 7-aryl-3,4,5,6-tetrahydro-2H-pyrido[4,5-b]- and [2,3-b]-1,5-oxazocine-6-ones

A convenient and diversity-oriented method for synthesis of the novel 7-aryl-3,4,5,6-tetrahydro-2H-pyrido[4,5-b]-1,5-oxazocine-6-one skeleton 1 and the very rarely described 7-aryl-3,4,5,6-tetrahydro-2H-pyrido[2,3-b]-1,5-oxazocine-6-one skeleton 2, featuring cyclization using nucleophilic aromatic substitution (S_NAr) and Suzuki coupling, is described.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

Synthesis of annelated [a]aza-anthracenones and thieno[3,2-g]aza-naphthalenones through ring transformation of 2H-pyran-2-one followed by photocyclization

A concise synthesis of some new classes of heterocycles (4-aryl-11-oxo-1,2,3,11-tetrahydro-1,3a-diaza-cyclopenta[a]anthracen-6-carbonitriles and 5-aryl-12-oxo-1,3,4,12-tetrahydro-2H-1,4a-diazabenzo[a]anthracene-7-carbonitriles) has been developed by the ring transformation of suitably functionalized 2H-pyran-2-one with α-oxoketene cyclic aminals to intermediates (8-aroyl-5-aryl-2,3-dihydro-1H-imidazo[1,2-a]pyridine-7-ylidene)-acetonitriles and (9-aroyl-6-aryl-1,2,3,4-tetrahydropyrido[1,2-a]pyrimidin-8-ylidene)-acetonitriles) followed by their photocyclization either in CHCl₃ or acetonitrile. This reaction was further explored for the synthesis of methyl 4-aryl-11-oxo-1,2,3,11-tetrahydro-1,3a,9-triaza-cyclopenta[a]anthracene-6-carboxylate, 4-aryl-11-oxo-1,2,3,11-tetrahydro-1,3a,9-triaza-cyclopenta[a]anthracene-6-carbonitriles, 5-aryl-12-oxo-1,3,4,12-tetrahydro-2H-1,4a,10-triazabenzo[a]anthracene-7-carbonitriles, 4-aryl-10-oxo-1,2,3,10-tetrahydro-9-thia-1,3a-diazadicyclopenta[a,g]naphthalene-6-carbonitriles and 5-aryl-11-oxo-1,3,4,11-tetrahydro-2H-10-thia-1,4a-diazacyclopenta[b]phenanthrene-7-carbonitriles from the similar reactions.     

An efficient synthesis of novel spiro[[8H]indeno[2,1-b]-thiophene-8,9′-fluorene] building block for blue light-emitting materials

We have developed efficient synthetic routes to obtain a novel building block spiro[[8H]indeno[2,1-b]thiophene-8,9′-fluorene] (SITF), a monothiophene-containing spirobifluorene analogue, and constructed blue light-emitting materials, including 2′,7′-bis([1,1′-biphenyl]-4-yl)-spiro[indeno[2,1-b]thiophene-8,9′-fluorene] (BBP-SITF) and 2′,7′-bis(9,9′-spirobifluoren-2-yl)spiro[[8H]indeno[2,1-b]-thiophene-8,9′-fluorene] (BSBF-SITF). BSBF-SITF has shown to be a stable blue light-emitting material with high PL quantum efficiency (89%) and unique regioselective feature at the C2 of thiophene, which indicate that BSBF-SITF will be useful for constructing complicated optoelectronic systems.     

Nucleophilic cyclization of 3-alkynylquinoxaline-2-carbonitriles into pyrido[3,4-b]quinoxalines

3-Alkynylquinoxaline-2-carbonitriles have been synthesized from 3-chloroquinoxaline-2-carbonitrile via the Sonogashira reaction. Treatment of 3-alkynylquinoxaline-2-carbonitriles with an alkylamine or ammonia has been shown to produce stable enamines, e.g., (Z)-3-(2-aryl-2-aminovinyl)quinoxaline-2-carbonitriles. Their base-induced cyclization gave the previously unknown pyrido[3,4-b]quinoxalin-1(2H)-imines or pyrido[3,4-b]quinoxalin-1-amines. 3-Alkynylquinoxaline-2-carbonitriles were directly transformed into pyrido[3,4-b]quinoxalin-1(2H)-imines by heating with an alkylamine and K₂CO₃ in DMF. The ionization constants, and absorption and fluorescent properties of the resulted pyrido[3,4-b]quinoxalin-1(2H)-imines were measured.     

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs containing benzo[b]thiophene/benzo[b]pyrrole

The synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating benzo[b]thiophene/benzo[b]pyrrole units is described.     

Convenient synthesis of 10H-indolo[3,2-b]quinolines and 6H-indolo[2,3-b]quinolines by sequential chemoselective Suzuki reaction followed by double C-N coupling

A convenient and regioselective synthesis of two series of indolo[2,3-b]quinolines, namely 10H-indolo[3,2-b]quinolines and 6H-indolo[2,3-b]quinolines, has been developed. The synthesis, proceeds in moderate to high yields, involving chemoselective palladium catalyzed Suzuki reaction of 2,3-dihaloquinolines with 2-bromophenylboronic acid, followed by a double Buchwald-Hartwig C-N coupling.     

DBU: a highly efficient catalyst for one-pot synthesis of substituted 3,4-dihydropyrano[3,2-c]chromenes, dihydropyrano[4,3-b]pyranes, 2-amino-4H-benzo[h]chromenes and 2-amino-4H benzo[g]chromenes in aqueous medium

We have reported DBU catalyzed one-pot synthesis of 3,4-dihydropyrano[3,2-c]chromenes, dihydropyrano[4,3-b]pyranes, 2-amino-4H-benzo[h]chromenes and 2-amino-4H-benzo[g]chromenes from aldehydes, active methylene compounds malononitrile/ethyl cyanocacetate, and 4-hydroxycoumarin/4-hydroxy-6-methylpyrone/1-naphthol/2-hydroxynaphthalene-1,4-dione in water under reflux. The attractive features of this process are mild reaction conditions, reusability of the reaction media, short reaction times, easy isolation of products, and excellent yields.     

Synthesis and characterization of benzo[c]thiophene analogs incorporating benzo[b]thiophene/1-hexylindole/benzo[b]furan

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical studies of the benzo[c]thiophene analogs are also reported.     

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.     

A one-pot synthesis and 1,3-dipolar cycloaddition of [1,2]dithiolo[4,3-b]indole-3(4H)-thiones

Treatment of N-substituted 2-methyl-1H-indoles 1 with S₂Cl₂ and DABCO in chloroform gave the corresponding [1,2]dithiolo[4,3-b]indole-3(4H)-thiones 5 by the addition of triethylamine in high yield. 1,2-Dithiole-3-thiones 5 underwent cycloaddition with one or two DMAD equivalents to afford either 2-(3-thioxo-1,3-dihydro-2H-indol-2-ylidene)-1,3-dithioles 10 or fused 4,5-dihydrothiopyrano[3,2-b]indoles 9.