Synthesis of 1,3-diarylbenzo[c]selenophenes

For the first time, syntheses of 1,3-diarylbenzo[c]selenophenes are reported involving a selenium transfer reaction of keto-alcohol/benzo[c]furan using Woollins reagent.     

Tandem addition-cyclization of o-ethynylphenyllithiums and isoselenocyanates: a convenient preparation of functionalized benzo[c]selenophenes

The o-bromoethynylbenzenes were lithiated with tert-BuLi in Et₂O followed by treatment with isoselenocyanate, and then EtOH was added as a proton source, producing the desired (Z)-3-methylidenebenzo[c]selenophenes as the sole 5-exo-dig mode cyclization products in one-pot with yields ranging from 54-87%. The iodocyclization of the o-ethynylphenyllithium with isoselenocyanate stereoselectively gave the (E)-1′-iodo-3-methylidenebenzo[c]selenophene, which was converted into the more functionalized benzo[c]selenophenes via the Suzuki- and Sonogashira-coupling reactions.     

Synthesis and characterization of fluorene tethered benzo[c]thiophene/benzo[c]selenophene analogs

Synthesis of 9,9-dialkyl/diarylfluorene based benzo[c]thiophene/benzo[c]selenophenes is presented. The synthesis of benzo[c]thiophene analogs is also realized with fluorene containing one or two thiophene units. The optical and electrochemical studies of fluorenyl benzo[c]heterocycles are correlated with their structures.     

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.     

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.     

One-pot synthesis of pyrrolidino- and piperidinoquinolinones by three-component aza-Diels-Alder reactions of in situ generated N-arylimines and cyclic enamides

An efficient synthesis of hexahydropyrrolo[3,2-c]quinolin-2-ones and hexahydropyridino[3,2-c]quinolin-2-ones has been developed in moderate to high yields by one-pot two-step aza-Diels-Alder reactions of N-arylimines, formed in situ from anilines and benzaldehydes, with cyclic enamides, formed in situ from 5-hydroxypyrrolidin-2-ones and 6-hydroxypiperidin-2-ones by BF₃·OEt₂-promoted dehydration in dichloromethane at room temperature. The hexahydropyrrolo[3,2-c]quinolin-2-ones were formed as a single exo-stereoisomer in most cases and hexahydropyridino[3,2-c]quinolin-2-ones were formed as a mixture of exo- and endo-isomers favoring the endo-diastereomer.     

Short and efficient access to imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives

Access to N-protected or N-free imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives as potential antiviral compounds was achieved in good yields from N-protected 7-amino-8-halo-2-methylimidazo[1,2-a]pyridines by catalytic coupling of terminal acetylenes under mild conditions using [PdCl₂(PPh₃)₂] or [Cu(Phen)(PPh₃)₂]NO₃.     

Novel 6-substituted benzothiazol-2-yl indolo[1,2-c]quinazolines and benzimidazo[1,2-c]quinazolines

The synthetic route to and a preliminary biological evaluation of novel indolo[1,2-c]quinazolines (8) and benzimidazo[1,2-c]quinazolines (9) are described. The products were obtained by condensation of the appropriate diamines (e.g. 2-(2-aminophenyl)indole or 2-(2-aminophenyl)benzimidazole) with 2-cyanobenzothiazoles. This work further demonstrates the general applicability of microwaves for a facile and rapid access to original heterocycles with potential pharmaceutical value.     

2-Oxobenzo[h]chromene: a novel entry for the concise and efficient synthesis of indeno[1,2-c]phenanthrenes

An efficient and concise synthesis of 7-sec-amino-5,13-dihydro-6H-indeno[1,2-c]phenanthrene-8-carbonitriles is described through base catalyzed ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with 1-indanone in moderate to 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.     

Enantioselective synthesis of chelidonine, a B/C-cis-11-hydroxyhexahydrobenzo[c]phenanthridine alkaloid

Both enantiomers of chelidonine, a B/C-cis-11-hydroxyhexahydrobenzo[c]phenanthridine alkaloid, were synthesized by manipulation of the B/C-dehydro ring juncture of benzo[c]phenanthridine skeleton using Sharpless asymmetric dihydroxylation and stereospecific catalytic hydrogenation after introduction of oxygen functions on the C ring as key reaction steps for the construction of stereogenic centers.     

Acid-catalyzed condensation of 2,2′-diamino-1,1′-biaryls for the synthesis of benzo[c]carbazoles

2,2′-Diamino-1,1′-biaryls were found to undergo ring-closure condensation reaction to afford benzo[c]carbazoles in good to excellent yield. Coupled with the synthesis of 2,2′-biaryldiamines from diaryl hydrazides via [3,3]-sigmatropic rearrangement, it constitutes a new efficient synthetic method for benzo[c]carbazoles and related compounds.     

Synthesis of 1-benzyl-8,9-dihydroimidazo[4,5-c]pyrrolo[3,2-g]quinolin-4(5H)-one via palladium-catalyzed intramolecular arylation

The synthesis of a novel tetracyclic structure, 8,9-dihydroimidazo[4,5-c]pyrrolo[3,2-g]quinolin-4(5H)-one, has been achieved by a convergent pathway. Coupling of the weakly nucleophilic hindered aromatic amine with 1-benzylimidazole-4-carboxylic acid, 7, afforded the corresponding amide 9 using a DCP/DMF complex; subsequent Heck-type arylation leading to desired tetracyclic molecule imidazo[4,5-c]-pyrrolo[3,2-g]quinolin-4(5H)-one.     

A convenient synthesis of partially reduced benzo[c]phenanthrenes, its ketals and ketones

A concise and convenient synthesis of various partially reduced 6-sec-amino-1,2,3,4,7,8-hexahydro-, 6-sec-amino-1,2,7,8-tetrahydrobenzo[c]phenanthrene-5-carbonitriles, 6-sec-amino-3,4,7,8-tetrahydro-1H-benzo[c]phenanthrene-2-one-5-carbonitrile cycloalkene ketals, pendant with electron donor and acceptor substituents has been described through base catalyzed ring transformation of 2-oxo-4-sec-amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles by cyclohexanone, 2-cyclohexen-1-one, 1,4-cyclohexanedione monocycloalkene ketals. The acid catalyzed deketalation of 6-sec-amino-3,4,7,8-tetrahydro-1H-benzo[c]phenanthrene-2-one-carbonitrile ketals led to yield 6-sec-amino-3,4,7,8-tetrahydro-1H-benzo[c]phenanthrene-3-carbonitrile-2-ones in excellent yield. We also performed the X-ray studies of the molecules 3d and 6a to know the degree of non-planarity.     

Construction of pyrazolo[3,4-b]pyridines and pyrazolo[4,3-c]pyridines by ring closure of 3-acylpyridine N-oxide tosylhydrazones

3-Acylpyridine N-oxide tosylhydrazones give good overall yields of a mixture of pyrazolo[3,4-b]pyridines and pyrazolo[4,3-c]pyridines when treated with an electrophilic additive and an amine base. (Z)-Hydrazones cyclize readily, while (E)-hydrazones fail to react under the reported conditions. The reaction takes place at room temperature, and moderate regiocontrol over the cyclization can be achieved by varying the electrophile/solvent combination.     

Synthesis of new benzo[b]thieno fused ring systems via transition metal-mediated cyclisations

The compact synthesis of a new ring fused benzo[b]thieno derivative with an embedded nine-membered ring system via ring closing metathesis methodology is described. The preparation of the novel 11H-benzo[b]thieno[2,3-c]pyrrolo[2,3-a]indol-11-one via palladium-mediated oxidative cyclisation of benzo[b]thien-2-oyl indole derivatives is also reported.     

Synthesis of polyarene derivatives of fused aziridines by Suzuki-Miyaura cross-coupling

A convenient and effective synthetic approach to potentially radiochromic polyarene derivatives of bi- and tricyclic aziridines utilizing modified Suzuki-Miyaura cross-coupling with catalysis in micellar media has been developed. A series of polyarene substituents were introduced into 1,5-diaryl-3,5a-dihydro-1H-azireno[1,2-c]imidazoles, 1,6-diaryl-1,3,4,6a-tetrahydroazireno[1,2-a]pyrazines, and 1,2-diaryl-1,1a-dihydroazireno[1,2-a]quinoxalines without degradation of the highly reactive aziridine ring system.     

Cycloalkano[1″,2″:4,5;4″,3″:4′,5′]bis(pyrrolo[2,3-c]pyrimido[5,4-e]pyridazines): synthesis, structure and mechanism of their formation

Reactions of 3-alkylamino-6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones with cyclohexyl- and cycloheptylamines in the presence of AgPy₂MnO₄ produce novel cycloalkano[1″,2″:4,5;4″,3″:4′,5′]bis(pyrrolo[2,3-c]pyrimido[5,4-e]pyridazines). Detailed information concerning the scope and mechanism of these transformations is discussed.     

Substituted chromones in [3+2] cycloadditions with nonstabilized azomethine ylides: synthesis of 1-benzopyrano[2,3-c]pyrrolidines and 1-benzopyrano[2,3-c:3,4-c′]dipyrrolidines

Chromones bearing electron-withdrawing substituents at the 2- or 3-position react with nonstabilized azomethine ylides to produce 1-benzopyrano[2,3-c]pyrrolidines in good yields. Reactions of 3-cyanochromones proceed diastereoselectively to give 1-benzopyrano[2,3-c]pyrrolidines and tetrahydro-1H-spiro[chromeno[2,3-c]pyrrol-9,5′-oxazolidine]-9a-carbonitriles, depending on the reactant ratio, as a result of a 1,3-dipolar cycloaddition of the azomethine ylide at the double bond and carbonyl group of the chromone system. The latter undergoes demethylenation and recyclization into a novel hexahydrochromeno[2,3-c:3,4-c′]dipyrrole tetracyclic system on heating with hydrochloric acid.     

A new synthetic approach to 7-hydroxynitidine

Benzo[c]phenanthridine alkaloid, 7-hydroxynitidine, was synthesized from readily available 2-benzyloxy-6-bromo-3,4-dimethoxybenzaldehyde 5 and napthylamine 6 using reductive amination followed by radical cyclization in eight steps. This method is highly efficient and better way to synthesize fully aromatized benzo[c]phenanthridine compounds.