Sequential approach to the synthesis of 'U and Z' shaped polycyclic heteroarenes

The synthesis of three new classes of heteroarenes, built through the sequential fusion of naphthalene, benzo/naphtho[b]oxepine and thiochromene rings with pyran and pyrimidine ring systems to give 'U and Z' shaped structural frameworks is reported. The methodology is based on the synthesis of pyran fused intermediates, 1-methylthio-3-oxo-5,6-dihydro-3H-benzo[f]chromene-2-carbonitrile (3), 4-methylthio-2-oxo-5,6-dihydro-2H-benzo/naphtho[b]pyrano[2,3-d]oxepine-3-carbonitriles (10, 20) and 4-methylthio-2-oxo-2,5-dihydrothiochromeno[4,3-b]pyran-3-carbonitriles (15) from the reaction of 2-tetralone, benzo/naphtho[b]oxepin-5-ones and thiochromen-4-ones with methyl 2-cyano-3,3-dimethylthioacrylate respectively. Further condensation of intermediates 3, 10, 20 and 15 with amidines led to the formation of tetracyclic 'U' shaped 4-amino-2-aryl-7,8-dihydro-5-oxo-5H-naphtho[2,1-b]pyrimido[4,5-d]pyrans (8) and 'Z' shaped 4-amino-2-aryl-5-oxo-12,13-dihydro-5H-benzo/naphtho[b]oxepino[5,4-b]pyrimido[4,5-d]pyrans (12, 22) and 4-amino-2-aryl-5-oxo-5,12-dihydrothiochromeno[4,3-b]pyrimido[4,5-d]pyrans (17). Compound 12f forms a chain of dimers through N-HO interactions as indicated by the X-ray structure analysis, and the quantum chemical calculations performed at the MP2 level indicate that this interaction energy is 10 kJ mol(-1).     

An unusual synthesis of tetrahydrobenzo[f]isoquinolines

A facile and short synthesis of 2-oxo-4-sec-amino-2,3,5,6-tetrahydrobenzo[f]isoquinoline-1-carbonitriles has been delineated through base catalyzed ring transformation of 5,6-dihydro-2-oxo-4-sec-amino-2H-benzo[h]chromene-3-carbonitrile by cyanoacetamide in excellent yields.     

The reaction of 2-hetarylacetonitriles with heterocyclic haloaldehydes

The reaction of 4-oxo-3,4-dihydroquinazolyl-and benzimidazolylacetonitriles with 2-chloro-2-quinolinecarbaldehydes and 1-aryl-5-chloro-3-methyl-1H-pyrazole-4-carbaldehydes gave the corresponding 3-(2-chloro-3-quinolyl)-2-(4-oxo-3,4-dihydro-2-quinazolyl)-2-propenenitriles and 3-(1-aryl-5-chloro-3-methyl-1H-4-pyrazolyl)-2-hetaryl-2-propenenitriles. Intramolecular cyclization of these compounds gives 15-oxo-15H-benzo[6,7][1,8]naphthyridino[2,1-b]quinazoline-6-carbonitriles, 1-aryl-3-methyl-11-oxo-1,11-dihydropyrazolo[4′,3′:5,6]pyrido[2,1-b]quinazoline-5-carbonitriles, and 1-aryl-3-methyl-1H-benzo[4,5]imidazo[1,2-a]pyrazolo[4,3-e]pyridine-5-carbonitriles.     

A non-catalytic approach to the synthesis of 5,6-dihydrobenzo[h]quinolines

A concise synthesis of highly functionalized 5,6-dihydrobenzo[h]quinoline-3-carbonitriles is delineated through base induced ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with S-methylisothiourea sulfate and 1-carboxamidinepyrazole hydrochloride, separately, in DMF. Under analogous reaction conditions the ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles by formamidine acetate provided 4-sec-amino-benzo[h]quinoline-3-carbonitriles in moderate yields, while with benzamidine hydrochloride, the reaction followed the same mechanism to yield 2-phenyl-4-sec-amino-5,6-dihydrobenzo[h]quinoline-3-carbonitriles.     

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.     

Cyclopropanation of N-substituted 3-aryl-2-cyanoprop-2-enamides and derivatives of 5,5-Dimethyl-2-oxo-2,5-dihydrofuran-3-carboxylic acid and 2-oxochromene-3-carboxylic acid with bromine-containing zinc enolates

Zinc enolates derived from 1-aryl-2,2-dibromoalkanones react with N-substituted 3-aryl-2-cyanoprop-2-enamides and 5,5-dimethyl-2-oxo-2,5-dihydrofuran-3-carboxylic and 2-oxochromene-3-carboxylic acid derivatives to give, respectively, N-substituted 2-alkyl-3-aryl-2-aroyl-1-cyanocyclopropane-1-carboxamides, 6-(4-bromobenzoyl)-4,4,6-trimethyl-2-oxo-3-oxabicyclo[3.1.0]hexane-1-carboxylic acid ethyl ester and morpholide, and 1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropla[c]chromene-1a-carboxylic acids as a single geometric isomer. Treatment of 1-alkyl-1-aroyl-2-oxo-1a,7b-dihydrocyclopropa[c]chromene-1a-carboxylic acids with carboxylic acid anhydrides leads to the formation of the corresponding 9c-alkyl-1-aryl-3,4-dioxo-9b,9c-dihydro-2,5-dioxacyclopenta[2,3]cyclopropa[1,2-a]naphthalen-1-yl carboxylates.     

Carbanion-induced base-catalyzed synthesis of 1H-isothiochromenes, benzo[c]thiochromenes through ring-transformation reactions of 6-aryl-2H-pyran-2-ones

An innovative approach to the one-pot synthesis of highly functionalized 3,4-dihydro-1H-isothiochromenes (3), 6H-benzo[c]thiochromenes (5, 6), 6H-benzo[c]chromenes (8), and 2,3-dihydro-1-benzothiophenes (10, 11) is delineated from the reaction of a suitably functionalized 6-aryl-3-carbomethoxy-4-methylthio-2H-pyran-2-one (1) and a carbanion generated from tetrahydrothiopyran-4-one, 4-thiochromanone, 4-chromanone, and tetrahydrothiophene-3-one through ring-transformation reactions.     

Versatility of 2-oxobenzo[h]chromene for the synthesis of oxabenzo[c]chrysenes

An innovative and concise synthesis of (7,8-dihydro-5-oxabenzo[c]chrysene-6-ylidene)acetonitriles is described through base catalyzed ring transformation of 2-oxo-4-piperidin-1-yl-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with 1-tetralone in very good yields.     

Synthesis of partially reduced ferrocenylphenanthrenes from 2-oxobenzo[h]chromenes through C-C insertion

An efficient and concise de novo synthesis of ferrocenyl tethered partially reduced phenanthrenes is described through base-catalyzed ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with acetylferrocene.     

An efficient and novel approach to the synthesis of tetrahydrophenanthro[4,3-b]thiophenes

An elegant approach to the synthesis of 2,3,6,7-tetrahydrophenanthro[4,3-b]thiophenes has been described through base catalyzed ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with tetrahydrothiophen-3-one in very good yields.     

Reaction between naphthols and dimethyl acetylenedicarboxylate in the presence of phosphites. Synthesis of stable oxa-2 lambda 5-phosphaphenanthrenes,and benzochromene derivatives

The reaction of dimethyl acetylenedicarboxylate (DMAD) with 2-naphthol in the presence of trimethyl or triphenyl phosphite leads to stable dimethyl oxa-2 lambda 5-phosphaphenanthrene derivatives in good yields. The reaction of DMAD and trimethyl phosphite in the presence of 1-naphthol or 8-hydroxyquinoline leads to dimethyl 2-(dimethoxyphosphoryl)-3-(1-hydroxy-2-naphthyl)succinate or dimethyl 2-(dimethoxyphosphoryl)-3-(8-hydroxyquinolin-7-yl)-succinate in excellent yields. Using triethyl phosphite and DMAD in the presence of 2-naphthol or 1-naphthol produces methyl 3-oxo-2,3-dihydro-1H-benzo[f]chromene-1-carboxylate or methyl 2-oxo-3,4-dihydro-2H-benzo[h]-chromene-4-carboxylate in excellent yields.     

Acetyltrimethylsilane mediated synthesis of dihydrophenanthrenes

An easy and efficient synthesis of phenanthrene derivatives through base catalyzed ring transformation of 4-sec-amino-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with acetyltrimethylsilane is described in good yields. The advantage of this reaction is the direct transformation of 2-oxobenzo[h]chromene into phenanthrene via C-C insertion from acetyltrimethylsilane.     

An efficient and versatile route to the synthesis of 9,10-dihydro-3-formylphenanthrenes

An innovative and efficient route to the synthesis of 9,10-dihydro-3-formylphenanthrenes 7 has been delineated through the ring transformation of 2-oxo-4-sec-amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles 4 with methyl glyoxaldimethylacetal 5 to masked 3-dimethoxymethyl-1-sec-amino-9,10-dihydrophenanthrene-3-carbonitriles 6 followed by deacetalation with Amberlyst 15 in excellent yields.     

Economical synthesis of novel class of heteroatom containing partially reduced polycyclic aromatic hydrocarbons

An efficient and convenient synthesis of 2-oxa- and 2-thia-3,4,7,8-tetrahydro-1H-benzo[c]phenanthrenes has been described through base-induced ring transformation of 2-oxo-4-sec.amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles by 4-oxotetrahydropyran and 4-oxotetrahydrothiopyran, respectively, in excellent yields.     

Reaction of 2-hetaryl-2-(tetrahydro-2-furanylidene)acetonitriles with aldehydes

The reaction of 2-hetaryl-2-(tetrahydro-2-furanylidene)acetonitriles with a electrophilic reagent (anisaldehyde) was studied. It was shown that condensation of the latter with 2-(4-oxo-3,4-dihydro-2-quinazolyl)- and 2-(1H-benzo[d]imidazol-2-yl)-2-(tetrahydro-2-furanylidene)acetonitriles in the presence of secondary amines or acids takes place with elimination of the furan fragment and the formation of 3-aryl-2-(4-oxo-3,4-dihydro-2-quinazolinyl)- and 2-(1H-benzo[d]imidazol-2-yl)acrylo-nitriles.     

Synthesis and structure elucidation of the condensation products between thiophene dicarbaldehydes and aromatic amines. Potential analgesic and anti-inflammatory agents

Thiophene-3,4-dicarbaldehyde 1 reacts in the presence of 2-mercaptoethanol to yield N-aryl-5,6-dihydro-4-oxo-4H-thieno[3,4-c]pyrroles 2 and N-aryl-4-arylimino-5,6-dihydro-4H-thieno[3,4-c]pyrroles 3 , while thiophene 2,3-dicarbaldehyde 4 reacts with aromatic amines to give N-aryl-5,6-dihydro-6-oxo-4H-thieno[2,3-c]pyrroles 5 in good yields. Labeling experiments and nmr spectral analysis give evidences for the possible reaction mechanism.     

Synthesis of alkyl 4-alkyl-2-hydroxy-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylates as peptidomimetic building blocks

A general synthesis of new alkyl 4-alkyl-2-hydroxy-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylate peptidomimetic building blocks from the corresponding alkyl 3-oxo-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylates through carbanion oxidation is described.     

An expeditious protocol for sesquiterpene-cored functionalized arenes from S-(−)-citronellal

An expeditious straightforward synthesis of sesquiterpene-cored arenes functionalized with electron-withdrawing or electron-donating substituents is described and illustrated by Michael addition of S-(−)-citronellal on functionalized 2H-pyran-2-one in a single step at room temperature. The reaction was further generalized by synthesizing isoprenylated 9,10-dihydrophenanthrene-2-carbonitrile using 5,6-dihydro-2-oxo-4-sec-amino-2H-benzo[h]chromene-3-carbonitriles and S-(−)-citronellal under similar reaction conditions.     

2-Oxobenzo[h]chromene: a novel entry for the synthesis of functionalized angular polycyclic azaarenes

An efficient and short synthesis of (5,6-dihydrobenzo[h]pyrido[2,1-b]quinazolin-2-ylidene)acetonitriles, (5,6-dihydrobenzo[h]pyrazino[2,1-b]quinazolin-2-ylidene)acetonitriles and (5,6-dihydrobenzimidazo[1,2-b]benzo[f]isoquinolin-7-yl)acetonitriles in good yields is delineated through base catalyzed ring transformation of 4-(piperidin-1-yl)-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles with 2-amino-pyridine, 2-aminopyrazine and (imidazo-2-yl)acetonitrile.     

Non-catalytic approach to the synthesis of partially reduced 'S' shaped dioxathia- and oxadithiahelicenes through base induced inter- and intramolecular C-C bond formation

An efficient and convenient route for the construction of helical 'S' shaped dioxathia- and oxadithiahelicenes with oxygen and sulfur atoms located in the middle of the outer helix has been developed through base induced inter- and intramolecular C-C bond formation from the reaction of 4-sec-amino-2-oxo-2,5-dihydrothiochromeno[4,3-b]pyran-3-carbonitriles with 3,4-dihydro-2H-benzo[b]oxepin-5(2H)-ones, 3,4-dihydrobenzo[b]thiepin-5(2H)-one and thiochroman-4-ones separately. Quantum chemical calculations have also been carried out to explore the geometries and electronic structures of newly synthesized compounds to envisage the pathway for interconversion of both atropisomers. The determination of helicity parameters and configurational stability demonstrate that the energy barrier is strongly dependent on the nature of hetero-atoms present.